Byron's Legacy

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Byron Hosking was a long standing member of the forum. He was very knowledgeable about many aspects of fish keeping with many years spent in the field researching and was always willing to share his knowledge. Many members of the forum have benefited from his expertise.

Sadly Byron passed away in early May 2024. He will be sadly missed by everyone on Tropical Fish Forums.

This thread contains many of the posts made by Byron; it preserves some of his vast knowledge so that current and future members may continue to benefit and learn from his wisdom.


#1 Hardness and Fish
#2 Use of Seachem Equilibrium and Bicarbonate
#3 The Importance of Regular Partial Water Changes
#4 The Importance of GH as a Parameter
#5 The Usefulness of Hitch-hiker Snails
#6 Acclimating Fish
#7 The Effect of Group Size on the Behaviour and Welfare of Fish
#8 The Effects of Light on Fish
#9 Nitrate and Fish
#10 Nitrate and Plants
#11 Substrate and Plants
#12 Scientific Naming of Fish


Hardness and Fish

Freshwater fish species have evolved over thousands of years to function best in a very specific aquatic environment. Water parameters is a significant aspect of environment. The fish's homeostasis, or physical equilibrium, is the complex chain of internal chemical and physical reactions that keep the fish living, from adjusting the blood pH, to digestion, to feeding its tissues, to maintaining a healthy immune short, living. The homeostasis only functions well when the fish is in the environment for which it was designed because the various factors of the environment--of which water parameters is one--affect the various processes either directly or indirectly.

To take just one simple example: when soft water fish are maintained in harder water than that for which their physiology is designed, the calcium extracted by the kidneys from the water that is entering the fish continually through every cell via osmosis (as well as in the gills) accumulates and slowly blocks the kidney tubes. Eventually the fish just dies, with no external signs of why. Studies have shown that the higher the calcium content (the harder the water) the shorter the lifespan before this kills the fish. Such a fish was managing or surviving, but not thriving. A shorter than normal lifespan almost always results, though fish can also die sooner from many other things such as some genetic problem, heart attack, etc.

This is a very important aspect of fish care because any extra effort the fish has to make to compensate for factors in the environment that are not compatible further drains the fish and causes stress. One author likened it to driving a car up a hill; it takes more energy to maintain the same speed uphill as on level ground, and in a fish this energy is being diverted away from essential biological processes just to compensate. And stress is the direct cause of 95% of fish disease, so avoiding stress or keeping it minimum goes a long way to having healthy fish. A simple will not contract ich even tough it is present, unless they are stressed by something. So keeping them in inappropriate water parameters causes stress and this means the fish will be more likely to develop diseases than otherwise.

Use of Seachem Equilibrium and Bicarbonate

There are a couple different things to sort out here, so I'll do my best.

First is the Equilbrium. This is a plant additive; Seachem will tell you if you ask that it should not be used to raise GH for fish specifically, as fish requiring a higher GH also need a higher pH and KH. I used Equilibrium for I think four years, to raise the GH from zero to 4 or 5 dGH, solely to supply sufficient calcium and magnesium for the plants. The pH remained below or around 5 which was fine as I only had/have soft water fish. However, again this is plant-oriented, not fish.

Second on the sodium bicarbonate. This is not safe for fish, and it is not permanent. As organics increase they can reduce the buffering capacity so you end up adding more and more...and the fish are the losers. Every substance added to the tank water ends up in the fish's bloodstream and then internal organs. This alone is reason to use additives cautiously, but it also should mean we only use the absolutely essential additives to do the job as best with minimal side issues. The "horrible chemical reaction" you mention is evidence of why all these additives are risky if not downright deadly. An aquarium is governed totally by the laws of science, be they chemistry or biology. Interfering in any one aspect is never safe unless it factors in all of the resulting effects.

Back in the 1990's I was persuaded by well-intentioned aquarists to "buffer" the pH, and I did this for several years by adding two or three tablespoons of dolomite in a nylon bag in the filter chamber. It raised the pH from 5 up to 6.5 to 6.6 and it remained stable for the years I used it. I stopped back in the early 2000's because I saw no reason, given that I have wild-caught very soft water fish. This topic of buffering came up on Ian Fuller's CorydorasWorld FB page a couple weeks ago, and Ian told me that he uses RO water with no buffering, and his wild-caught Corydoras spawn and live with no difficulty, in spite of the zero GH and KH and a pH below 5.

Turning to the GH issue. Each species of freshwater fish has evolved over thousands of years to function in a very specific environment, which includes the water parameters. When the parameters are those for which the particular species' physiology is designed, it will function with the least amount of stress and difficulty. As soon as those parameters begin to shift away from the preferred or normal for that species, the fish has more trouble just carrying out the normal everyday life processes. This adds stress which further weakens the fish. The fish will succumb to issues like disease that it would otherwise and should be able to deal with, but being weakened it cannot.

GH is the most important parameter (perhaps equally with temperature, since both have such large impacts on a fish's physiology). The GH is the level of dissolved calcium and magnesium (primarily) in the water. Some fish species have evolved to require this, others do not. Fish requiring harder water (higher GH) will slowly weaken in softer water, and if they do not succumb to something along the way they will inevitably have a much shorter than normal expected lifespan. Similarly, soft water species kept in water that has a higher GH will assimilate the calcium from the water that continually enters via osmosis through every cell on their body. This water passes through the kidneys and the minerals are extracted--the fish has no control over this, it is how they function; as this continues, the kidneys become blocked and the fish dies. There are no external indications, but a necropsy will identify calcium deposits in the kidneys. A study in Germany in the 1980's determined that the higher the GH, the shorter the lifespan of cardinal tetras, and the cause of death was calcium blockage.

The pH will geenerally be tied to the GH and KH. If the water has a high GH, usually the KH is comparable and the pH will be basic (above 7). In soft water the GH is naturally low, and usually the KH and pH correspond. There are some exceptions of course, but we are dealing in general terms here. Amazon waters are very soft, and the pH is acidic. Waters in Central America have a higher GH and the pH is basic. The water in the rift lakes is similar, high in GH, KH and pH.

The Importance of Regular Partial Water Changes

Byron Hosking
November, 2010 (rev April 2021)​

Nothing is more important when it comes to aquarium maintenance than regular partial water changes. The adage “an ounce of prevention is worth a pound of cure” certainly applies here.

One frequently reads of products that will reduce the need for water changes. Chemical media (carbon and such) may adsorb, absorb or change certain pollutants, but there is a finite limit to this and in some cases the pollutants return to the aquarium water in a different form that is still harmful. Some forms of bacteria will also release these adsorbed pollutants back into the water. And such chemical media frequently also adsorb beneficial nutrients which further worsens the state of the aquarium. Water changes also replenish essential substances such as minerals and ions. In the final analysis, there is no amount of filtration with any media that can duplicate the benefit of a regular partial water change. Almost everything that has or can have a detrimental effect on the fish or the biological system that goes into an aquarium remains there in some form until we remove it.

The water in the fish’s natural habitat is not static but constantly changing. There are water currents in streams and rivers; thermal currents in ponds and lakes; a regular influx of fresh water from rain and snow melt. Aside from all this, the ratio of water volume to fish is infinitely greater than what we maintain in any home aquarium. The toxins the fish expel—which include ammonia through respiration, solid excrement, urine, pheromones, and allomones—are regularly being dispersed. In nature, these substances are dealt with “naturally,” but the aquarium is a closed system and the operation of nature is greatly restricted. This “crud” is partially handled by filtration (and some but certainly not all with live plants), but no matter how much filtration you have on your aquarium, crud in some form continues to accumulate (Boruchowitz, 2009). The regular partial water change improves this situation considerably by injecting fresh water into the system as it removes a given quantity of the toxins. This is very important to the long-term health of the fish, and live plants will benefit too. The volume and frequency do somewhat depend upon the specifics of the aquarium, but as will be evident throughout this article, there can be no doubt whatsoever that the more water that is changed and the more frequently, the healthier will be the fish. And water stability is virtually impossible otherwise.

An aquarium without regular water changes is like living in a sealed room without fresh air. Anyone who has worked in an air-sealed office building knows about this; regardless of the air conditioning system, it just is not the same as opening the window for fresh air. Like that air, the water in the aquarium becomes stale very quickly. Fish are constantly (day and night) taking in water via osmosis through every cell; many of the substances we add to "improve" the water can diffuse across the cell membrane with the water, and often these too are dangerous. The water enters the bloodstream and is carried to internal organs; the kidneys remove the minerals and expel the waste water along with any pollutants removed by their kidneys; an average-sized tetra produces 1/3 of its body weight in urine every day, so this quickly accumulates.

Many aquarists wrongly assume that a rise in nitrates (or a drop in pH) is the trigger for a water change. But this is waiting too late; the health of the fish and the aquarium’s biology has already been compromised if it shows up in these tests. The whole idea behind regular partial water changes is to prevent this from occurring, by maintaining a truly stable biological system.

1. Removing pollutants

The natural bacterial processes that break down toxins in the aquarium do not remove them completely, but change them into another form that may be less but nonetheless still toxic; an example understood by most aquarists is the nitrification cycle whereby ammonia is changed into nitrite which is then changed into nitrate. More recent scientific studies have determined that nitrate levels above 20ppm are detrimental to most fish in our aquaria, and some will be negatively impacted even at 10ppm.

And there are many others. Waste can be processed but it remains—until the water is changed.

Pheromones and allomones. These are chemical substances released by fish, plants, and algae. Biology Online defines them thus:

Pheromones: chemical substances which, when secreted by an individual into the environment, cause specific reactions in other individuals, usually of the same species. The substances relate only to multicellular organisms. This includes kairomones [these are released by flowers].​

Allomones are repellent pheromones that induce a behavioural or physiologic change in a member of another species that is of benefit to the producer.​

Just as hormones affect the body they are in, so pheromones and allomones released into the environment affect the bodies of other fish. These vary in function: some are used as communication between fish of the same species in a shoal—sometimes as a warning of danger, or the presence of food; some initiate spawning behaviour between mates; some limit and even prevent growth of both the fish that releases them and other fish in the tank; some are warnings of aggression to other fish; and some indicate the fish is under stress.

Reduction in microbial populations and their metabolites. Microbial population refers to all those microorganisms living in the aquarium water; included are pathogens—microorganisms such as a virus, bacterium, prion, or fungus, that causes disease. Maintaining fresher, more stable water by removing all these pollutants is one of the easiest ways to keep the fish healthy. Regular water changes can also help to keep algae from increasing.

2. Water Stability

This encompasses a number of factors. GH (general mineral hardness) and electrolytes must be replenished, and this requires either a water change or additives. Fish physiology will only function at its best under stable and appropriate levels, and these are important for the fish’s osmoregulation. Maintaining proper and stable pH and KH (carbonate hardness or Alkalinity) is also tied to regular water changes.

DOC (dissolved organic carbon) accumulates, and while this can be assimilated by plants, it is easy for DOC to overwhelm the aquarium, particularly one without plants, and this has serious consequences for the fish.

Nitrogenous substances in the water column such as ammonia and nitrite can be removed before they enter the nitrification cycle and thus help to keep nitrates lower. This is again more important in tanks without live plants. A rise in nitrates including any increase from one water change to the next indicates a biological imbalance.

Total dissolved solids (TDS) refers to the content of all organic and inorganic substances that are present in the water in a molecular, ionized or micro-granular suspended state. These build up from many sources: water conditioners and any substance affecting water chemistry; fish foods; organic matter; ions, minerals, salts and metals. As TDS increase, the ability of the water to hold oxygen decreases proportionally. The level of TDS also affects fish directly [see my article on stress for more detail]. TDS can only be effectively and significantly removed by water changes.

Replacing trace elements and minerals (significantly more critical for harder water species than very soft). These are important to the health of the fish, as well as the stability of the water chemistry. Over time they are used up or filtered out. If they aren't replaced, the pH of the water will drop. Furthermore, the lack of trace minerals will adversely affect the vigor and health of the fish and plants.

3. How to Do a Partial Water Change

Stating the obvious, a percentage of water in the aquarium must be siphoned out and then replaced with fresh water. The substrate may or may not need to be cleaned during the removal of the tank water. In planted tanks, it is best to leave most of the substrate untouched; in non-planted tanks cleaning of the substrate is usually recommended to remove waste and other organics that in the absence of live plants will likely increase nitrates. [For more on this, see my article Bacteria in the Freshwater Aquarium.]

Devices made for water changes allow cleaning (or vacuuming) of the substrate without pulling the substrate material out. These work well with any gravel substrate; with sand substrates, it is best to lightly vacuum only the top so that the sand is not also sucked out.

Water changes in larger tanks are tedious using a water changer and a pail. The automatic “Python” apparatus that connects directly to a faucet is recommended, or a do-it-yourself version.

Water conditioner should be added either directly to the water if using a pail, or to the aquarium as the water begins to enter if using a “Python” device. Sufficient conditioner for the volume of water being changed is adequate in either situation. If the aquarium holds especially sensitive fish, increasing the amount of conditioner may be advisable. Although most manufacturers say the product is not harmful if overdosed, this is misleading; all conditioners increase the TDS (total dissolved solids) and they are chemicals and they can enter the fish.

4. When not to do large water changes

As the bio-filtration cycle operates, whereby Nitrosomonas bacteria convert ammonia (produced by the fish continually) into nitrite and then Nitrospira bacteria convert the nitrite into less harmful nitrate, a by-product is the production of acids. Normally the buffering capacity of the water keeps this from becoming problematical, and the regular water changes are part of this safety net. Without water changes for several weeks, the acids accumulate; the larger the fish or the more there are, the more acids. We call this “old tank syndrome,” and as this is gradual, the fish adapt (in a false sense really) with it. There comes a point when the buffering capacity in the water is maxed out, and the pH starts to fall, and if it drops to the low 6's the good bacteria can't function and ammonia starts to build. In acidic water ammonia ionizes into less toxic ammonium which allows the fish to survive. Everything continues to look OK from the outside. Then you finally do a water change, which in this situation can be deadly.

The tap water pH will most probably be much higher than the pH of the tank water, and the more alkaline the tap water is, the worse will be the result. When half of the water in the tank is replaced with this fresh alkaline water, the pH in the tank rises and if it rises above pH 7 the ammonium in the tank water will change back into ammonia which is highly toxic, and the fish will succumb. The change in pH has a part to play as well, since the fish have to work extremely hard to readjust their internal pH to survive such a significant rapid shift in the external pH, and this weakens them which only adds to the problem. It takes time for the Nitrosomonas bacteria to multiply to an adequate number to handle the sudden increase in ammonia, and similarly for the Nitrospira bacteria to handle the subsequent increase in nitrite. This mini-cycle is relatively short by comparison to a new tank, but it is just as stressful on the fish. In a thickly planted tank, where the pH is normally slightly acidic on purpose, the plants are able to take up much of the ammonium, which means the final result would not be quite as disastrous.


Boruchowitz, David E. (2009), “Time for a Change: A Mathematical Investigation of Water Changes,” Tropical Fish Hobbyist, November 2009 (Part 1) and December 2009 (Part 2).

Evans, Mark E. (2004), “The Ins and Outs of Osmosis,” Tropical Fish Hobbyist, February 2004.

Muha, Laura (2006), “Fish Growth vs. Tank Size” in ‘The Skeptical Fishkeeper’ column, Tropical Fish Hobbyist, December 2006.

Strohmeyer, Carl (2011), “Reasons for Water Changes,” American Aquarium Products website:

“Growth Inhibiting Substance(s) of Fishes,” on the Wet Web Media at

"Is Nitrate Toxic? A Study of Nitrate Toxicity" on the site.
The Importance of GH as a Parameter

In another thread, I was asked if I had scientific data to support my frequent advice that GH was the more important parameter when compared to pH [temperature is another critical parameter but outside this particular discussion], and rather than hijack that thread, perhaps start a discussion here. So, here I am, (hopefully) with some evidence.

I am going to begin by pointing out that attempts to adjust the pH on its own are almost always worse than leaving it alone--unless you go about it the correct way. And that begins with the GH (general or total hardness) and KH (carbonate hardness, also termed Alkalinity by some). The GH and KH act to buffer the pH, preventing any changes, depending upon the level of GH/KH. This is why you must first ascertain these levels in your source water. Usually the higher the GH/KH, the higher the pH, but not always. But I can guarantee that if you ignore the GH/KH, and it happens to be high enough to effectively control the pH, all your additions of chemicals to lower the pH will only stress the fish and eventually kill them.

Now to a consideration of how GH affects fish.

First, a synopsis of a study reported a couple decades ago, but the age is irrelevant as we are dealing with scientific evidence/fact in the data. It was an article in Tropical Fish Hobbyist, August, 1987, pp. 66-87 [yes, lengthy, a lot of data/information], entitled "Ecology of the Cardinal Tetra, Paracheirodon axelrodi (Pisces, Characoidea), in the River Basin of the Rio Negro, Brazil, as well as Breeding-related Factors," authored by Rolf Geisler and Sergio R. Annibal. This article is important for other aspects of cardinal tetra care such as their extreme light phobia (they avoid waters that are not deep dark) and their avoidance of flowing currents whenever possible, but these factors will have to wait for another post!

The reference to parameters began with collection data of the species' habitats along both north and south tributaries of the Rio Negro. The authors defined typical blackwater streams in the catchment area of the Rio Negro as follows:
pH <4.3
Ca (calcium) and Mg (magnesium) < 1 mg/l [mg/l = ppm]
and they continue: "If all the limnochemical findings available from P. axelrodi biotopes are evaluated, the following water composition arises:
pH values 3.97 - 5.1
Total hardness 0.00 - 0.03 dGH

There is very worth-while data respecting the pH as a controlling factor in the habitat sources of P. axelrodi; it largely avoids or is found in greatly reduced numbers in waters having a pH below 5, and the authors conclude that this is not a "typical" black-water species if such fish do actually occur. But it is the GH that is behind this post, and there is some convincing data. Citing direct from the article (p. 79):

Investigations by G. Schubert on young P. axelrodi caught in April, 1982, in the Igarape Mamole-Rio Cuiuni and brought to Germany in the original water provide an important clue. At the Hohenheim Zoological Institute some fish were put into a mixture of water from Lake Constance and completely salt-free water in the ratio of 1:9. These fish, after only 7 months, showed a more or less pronounced blockage of the kidney tubuli with amorphous, strongly refractive matter. Calconephrosis is suspected. When 4 more animals were dissected at the end of June 1983, the blockage of the kidney tubuli had become very severe.​

The article goes on to mention that breeding strains in the USSR over the previous several years have had success breeding this species in harder water, up to 12 or 15 dGH. It dos not delve further into this.

Hard-water fish species have a sort of opposite problem. Thy must have calcium (primarily) in the water, at sufficient levels to provide them with the minerals essential to the operation of their internal life processes. Like their soft-water cousins, they evolved in very specific water, and in their case it is mineral-rich, so their physiology evolved to function in such water. It might be that the GH level is of more importance to hard-water fish than soft. But it is certain that a very low GH (amounting to very soft or soft water), regardless of the pH, is not going to provide a healthy life for such fish. I will get into this more in a subsequent post.

First, the habitat conditions tell us what the fish requires to be in good health, assuming that is our goal--healthy fish. Acidic conditions is fine, ideal in fact, for soft water fish. But you cannot keep hardwater fish in soft water without causing them internal problems, leading to a shorter lifespan whether from those problems or from other health issues they cannot fight off due to the weakened state from the inappropriate water parameters.

As for a balanced healthy aquarium one should never se ammonia at levels that can harm fish. Floating plants alone will ensure this. And good maintenance and husbandry.

The Usefulness of Hitch-hiker Snails

The topic of "hitch-hiker" snails and how to control/eliminate them arises frequently on TFF. In one such thread yesterday, I was questioned with respect to my views on the matter, so I thought it was advisable to confer with my friend Neale Monks. I now have a much more accurate understanding than I had up to now.

Before getting to the chase...many aquarists know the name Neale Monks. A former palaeontologist at the Natural History Museum in London, where he worked primarily on heteromorph ammonites, he has authored many articles, is a regular advisor for the UK magazine Practical Fishkeeping, a primary source for information on Wet Web Media, and without question one of the most highly respected and knowledgeable professionals in this hobby. Now to the chase.

Any organism added to an aquarium that can/will break down organic matter will add to the biomass. However, anything not consumed by the snails would be broken down by saprophytic bacteria and fungi, primarily in the filter, and these would themselves be adding to the biomass. These are the ammonification bacteria, and quite separate from the nitrifying bacteria.

Snails will be adding something to the workload of the bacteria, but so would the microbes breaking down the same dead plants and fish wastes anyway. The standing crop of snails at any given moment is probably greater than that of microbes doing the same job, but the impact of either on water quality will be very slight compared to adding too many fish. A complicating factor however is that snails also eat algae and microbes directly, and obviously this contributes to the bioload.

Neale's two summary paragraphs I will cite verbatim as I couldn't say it any better.

Yes, snails will be adding something to the biomass, but no, ordinarily it's not going to be much compared with the fish. Yes, they consume some organic material in the tank, but if they didn't, fungi and bacteria would do that anyway. You could even argue that by physically breaking down large pieces of detritus into smaller particles, they are increasing the surface area available for saprophytes to work with, speeding up the ammonification side of the water quality management process.​
I find it hard to get worked up over snails. In a balanced, well-run tank they rarely do any harm, and even where you have hundreds of Melanoides snails, the chances are they're not actually doing much harm in terms of water quality.​
I tried to summarize Dr.Monks' information previously, so I may not have been all that clear when it comes to this aspect. I have previously been saying that snails are just processing what is already there, not adding anything, but clearly this is inaccurate on both counts. So it may help if I just cite Neale's information.

What limits biomass is energy throughput. In theory, if an organism is added to a tank that can break down organic material that would otherwise end up in the filter, that organism would add to the biomass of the tank. So, if snails are eating 'food' that is otherwise unused in the tank (such as dead plant material) yes, they would add to the biomass per cubic metre of water.
With that said, the biological filter is the key thing here! Anything not consumed by the snails would end up in the filter, and such material would be broken down by fungi and bacteria anyway. And they would be adding to the biomass themselves. Perhaps not noticeably, but they'd be adding something. Since each bacterium has a short lifespan, there isn't the persistent mass of them visible in the same way as a single snail, but in terms of mass of bacteria that live and die across months or years, it'd presumably work out similar.
Also important: the idea that fish faeces are eaten by snails, and their faeces are eaten by more snails, and so on, is bogus. If nothing else, there's diminishing returns each time food passes through the gut of something. If there's 100 joules of energy in the food your fish eats, some fraction, say, 10 joules comes out as faeces. Some nutrients, like protein, will be better absorbed than other nutrients, and water soluble vitamins and minerals are lost very quickly, So while it's true some fish faeces might be eaten by snails, it's not going to be a massively rewarding source of food for them.
Since snails have a very low metabolic rate, the amount of oxygen consumed, and ammonia excreted, is generally negligible compared with the fish in an aquarium.
But they will be adding something to the bio load of the tank -- but then again, so will the saprophytic bacteria and fungi breaking down organic material in the tank as well. (These are the ammonification bacteria by the way, and quite separate from the nitrifying bacteria we use to clean the water.)
Acclimating fish

I don't know why but I thought drip acclimation was what all hardcore enthusiasts did because it was the most humane and least likely to stress the fish.

This is another myth. Fish cannot "adapt" to certain parameter changes (these are GH, pH) within a few hours, or days, it takes weeks. So drip acclimation is not helpful for these. Temperature however is a very different thing, floating the bag for 10-15 minutes to equalize the temperature is probably a good idea. Not everyone agrees, but it is a biological fact that fish do have difficulty if temperature changes are too rapid, so it makes sense to spend the 15 or so minutes to avoid this.

Fish are able to manage an upward temperature better than a downward, all else being equal. Temperature is very important because it drives the fish's metabolism.

Effect of Group Size on Behaviour and Welfare of Fish

The number of fish needed for species "x" to be healthy and less stressed in an aquarium is a topic that enters quite a number of threads on TFF. Some of us realize how vitally important the number of fish for a particular species really is, but having scientifically-controlled studies that provide concrete evidence has been largely lacking. One such study is "The effect of group size on the behaviour and welfare of four fish species commonly kept in home aquaria," authored by Amelia Saxby, Leoni Adams, Donna Snellgrove, Rod W. Wilson, and Katherine A. Sloman in the journal Applied Animal Behaviour Science, 125 (2010), pp. 195-205. This paper is available online (free) and I will include the link at the end of my post. The authors are marine biologists or similar, based in the UK, and the majority of the following is cited directly from this paper.

"Functioning-based” approaches to animal welfare aim to ensure the animal is functioning naturally on a biological level while a “natural behaviour” approach defines good welfare as being when an animal is free to fulfil its natural behaviour (Duncan and Fraser, 1997). More recently the “five freedoms” approach to animal welfare has been put forward where in order to guarantee welfare, animals should be free from: (a) hunger and thirst; (b) discomfort (an appropriate environment including shelter should be provided); (c) pain, injury and disease; (d) restriction of normal behaviour (including lack of space); (e) fear and distress (Farm Animal Welfare Council, 2009).

The welfare of four commonly kept species of ornamental fish (neon tetras, white cloud mountain minnows, angelfish and tiger barbs) was investigated in relation to group size. Behaviours including darting, aggression, shoaling and latency to feed were found to vary with group size in a species-specific manner. Each species was kept in specific group sizes in individual tanks. For neon tetras and white cloud mountain minnows, group sizes were one, two, five and 10 fish per tank; for angelfish the group sizes were one, two, three and five fish per tank, and for tiger barbs they were initially one, five and eight fish per tank.

It is important to note that for "ethical reasons," the Tiger Barb groups of one and five were removed and only the tank with ten was used; elevated aggression between groups of two and three individuals was noted as soon as they were placed together in the tank. Therefore, as holding tiger barbs at these stocking densities was likely to result in lasting harm, these treatments were terminated immediately. [Sound familiar?]

Neon tetras and white cloud mountain minnows displayed reduced aggression and darting and spent more time shoaling in the larger groups. Both species were most aggressive when held in groups of two and five. Behavioural patterns were more variable in angelfish and tiger barbs although larger group sizes resulted in increased shoaling. The results indicate improved welfare in larger groups of neon tetras, white cloud mountain minnows and tiger barbs. In angelfish, aggression was not reduced with greater numbers, but recognizing that this species naturally requires greater shoal numbers suggests that the need to defend territories or maintain social position causes aggressive actions to persist regardless of the shoal size.

I have dealt with aggression as this is a significant aspect of keeping these fish; the study delves into the other aspects which are equally interesting. There is a lot to be learned here.

Effect of Light on Fish

Fish are affected by light in many ways. There are several well-documented studies on spawning in some species being triggered by changes in the day/night cycle, and the hatching of eggs and the growth rate of fry can be impacted significantly depending upon the presence and intensity of light. The health of fish is closely connected to the intensity of the overhead light, various types of light, and sudden changes from dark to light or light to dark. To understand this, we must know something about the fish’s physiology. The primary receptor of light is the eye, but other body cells are also sensitive to light.

Fish eyes are not much different from those of other vertebrates including humans. Our eyes share a cornea, an iris, a lens, a pupil, and a retina. The latter contains rods which allow us to see in dim light and cones which perceive colours; while mammals (like us) have two types of cones, fish have three—one for each of the colours red, green and blue. These connect to nerve cells which transmit images to the brain, and the optic lobe is the largest part of the fish’s brain.

These cells are very delicate; humans have pupils that expand or contract to alter the amount of light entering the eye and eyelids, both of which help to prevent damage occurring due to bright light. Fish (with very few exceptions such as some shark species) do not have eyelids, and in most species their pupils are fixed and cannot alter. In bright light, the rods retract into the retina and the cones approach the surface; in dim light the opposite occurs. But unlike our pupils that change very quickly, this process in fish takes time. Scientific studies on salmon have shown that it takes half an hour for the eye to adjust to bright light, and an hour to adjust to dim light. This is why the aquarist should wait at least 30 minutes after the tank lights come on before feeding or performing a water change or other tank maintenance; this allows the fish to adjust to the light difference.

The Day/Night Cycle

Most animals have an internal body clock, called a circadian rhythm, which is modified by the light/dark cycle every 24 hours. This is the explanation for jet-lag in humans when time zones are crossed—our circadian rhythm is unbalanced and has to reset itself, which it does according to periods of light and dark. Our eyes play a primary role in this, but many of our body cells have some reaction to light levels. In fish this light sensitivity in their cells is very high.

Previously I mentioned that the rods and cones in the eye shift according to the changes in light. This process is also anticipated according to the time of day; the fish “expects” dawn and dusk, and the eyes will automatically begin to adjust accordingly. This is due to the circadian rhythm.

This is one reason why during each 24 hours a regular period of light/dark—ensuring there are several hours of complete darkness—is essential for the fish. In the tropics, day and night is equal for all 365 days a year, with approximately ten to twelve hours each of daylight and complete darkness, separated by fairly brief periods of dawn or dusk. The period of daylight produced by direct tank lighting can be shorter; and the period of total darkness can be somewhat shorter or longer—but there must be several hours of complete darkness in the aquarium. The dusk and dawn periods will appear to be stretched out, but that causes no problems for the fish. It is the bright overhead light that is the concern, along with having a suitable period of total darkness.

This period of total darkness includes ambient light in the room. If there is light in the room from lamps and such, the fish will not respond normally.

Turning the Tank Light On/Off

When the tank light suddenly turns on in a dark room, fish will dive to the substrate, dash about frantically often hitting the glass sides of the aquarium, or even jump out of the water. The same reactions occur when the tank lights are suddenly turned out. Aside from any possible physical injury the fish may sustain, these sudden changes in the light cause significant stress to the fish. Bright camera flashes can also be stressful in the same way. So also would any unnatural effect such as strobe lighting.

Thom Demas, curator of fishes at the Tennessee Aquarium, defines stress as anything that threatens to disrupt an organism’s normal physical, mental and/or emotional state. The organism must then expend energy dealing with the stressor, which leaves it with less energy to deal with other things, such as pathogens. “If the fish are busy running from or hiding from that weird phenomenon of ‘instant lights on or off,’ they may be wasting energy to this stressor and eventually get sick from something that is most likely ubiquitous and that they would have tolerated had the stressing event not been there,” says Demas. There is now ample scientific evidence that in fish as in humans, stress at any level has a very negative impact on the immune system because it disrupts the physiological equilibrium of the fish.

The solution with tank lights is obvious: the room should always be reasonably well lit when the tank light comes on and when it goes off. As Marc Kind, curator of fishes and invertebrates at the Adventure Aquarium in Camden, New Jersey, says, “this is just good, sound husbandry.” Given the evidence mentioned previously of the time it takes for fish to adjust, the room should be lit for at least an hour before and after the tank light is turned on or off respectively. From my own experience this all but eliminates any frantic reactions from the fish. They will uniformly and quickly swim toward the room light source (be it light coming in the window or from a lamp) when the tank light goes off, but without frantic crashes and jumping into the tank cover glass which will otherwise occur.

Nitrate and Fish

A clarification on nitrates. Ammonia, nitrite and nitrate are toxic to fish, period. They work differently, but all three are still toxic. Fish do not acclimate to high nitrates, at any rate not beneficially. Nitrate is slower acting, and it affects some species more than others. Fish are more likely to die from being weakened and succumbing to something else (such as disease) rather than dying from the high nitrates directly, if that makes sense.

Cichlids have problems with nitrates more than some fish. The cichlid sites are now advising that it is nitrate that is largely responsible for hole in the head (hexamina), and suggest keeping nitrates well below 20 ppm.

Nitrates in tropical water courses are zero or so close they might as well be zero. This is the water the fish evolved in. The lower the nitrate in the aquarium, the better. But fish do not acclimate to it, they slowly weaken and die from it.

Nitrate and Plants

Most aquarium plants prefer ammonia/ammonium, and will ignore nitrate if the ammonia/ammonium is in balance with all other nutrients and the light. They will not switch to nitrate (or nitrite) under normal circumstances (low-tech, natural method planted tank) because chances are the light and other nutrients (esp carbon here) will not be sufficient. And it takes plants about 24 hours to change gears. And, when they do, they have to then spend considerable energy changing the nitrate back into ammonium so they can use it. So, it is not surprising that they tend to ignore nitrate. [In high-tech systems it is very different.]

Diana Walstad goes into all this is great detail in her book Ecology of the Planted Aquarium, citing numerous scientific studies.

Also, there is denitrification. Bacteria that use nitrate to create oxygen. And, there is the change from nitrate to nitrogen gas that then escapes back into the atmosphere at the surface.

Substrate and Plants

There are no plants that need soil, all will grow in inert sand or fine gravel. And there are serious issues with any soil, bacterially and water quality.

Substrate must be suitable to the fish. Substrate fish like cories, loaches, cichlids are best with sand. All fish will be fine with sand. So this is your best option. Just make sure it is inert, unless it is going into a hardwater species tank.

Scientific Naming of Fish

I got asked this question on another forum so I put together this explanation.

The scientific name assigned to each living species is absolutely unique. Common names frequently vary so they are not reliable for identification. Every living organism has only one unique and internationally recognized scientific name.
A binomial nomenclature system is used to name all life, botanical and zoological; simply put, “nomenclature” means the names along with the system used to assign those names, and “binomial” means two names. These two are the genus (plural genera) and the species (or specific epithet). This system was developed by a Swedish botanist, zoologist and physician named Carl Linnaeus who lived from 1707-1778. In 1735, Linnaeus published his Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis; in translation, “System of nature through the three kingdoms of nature, according to classes, orders, genera and species, with [generic] characters, [specific] differences, synonyms, places.” Usually referred to as simply Systema naturae, by the thirteenth edition in 1767 it had become a monumental classification of all then-known species of life on earth. The system further developed into modern Linnaean taxonomy, the hierarchically-organized biological classification that is today used to classify all species of animals and plants. Strict rules govern this system, established and enforced by the International Code of Zoological Nomenclature [ICZN].
The scientific name (genus and species) is the last and most specific in the hierarchy of scientific classification. The genus is part of a Family, and the Family belongs to a certain Order; for our purposes, we do not need to go higher than the Order. The Family and Order can each be further divided into “Super” and “Sub” families and orders. Each of these terms includes “clades” or clusters of fish that are phylogenetically related. Phylogeny is sometimes referred to as the natural relationships and is an attempt to construct the history of all life based on the evidence from both living and fossil organisms. When classifications are based on phylogenies we can ascertain (and predict) how that group of related fish function, and since this tells us something about their behaviours and requirements it is of interest to aquarists.
Defining “species” is very complex; for our purposes, we may simply consider that the species is the individual fish that is unique from all other fish species. When two or more species are phylogenetically related they will be combined in the same genus. As an example, all fish in the catfish genera Aspidoras, Brochis and Corydoras have a very similar general appearance, easily recognized; but beyond this they share phylogenetical relationships more closely than they do with any other species. Certain specific relationships exist within the species, certain other specific relationships exist between all the species in the genus, and still other relationships exist between all three of the genera within the Family. As an example, Brochis splendens and Corydoras aeneus are almost identical in colouring and pattern; but they are in separate genera because of the rays in the dorsal fin; all Corydoras species have seven rays in the dorsal fin, while all Brochis species have more than ten rays in the dorsal.
Anyone may describe a new species and name it, but this is usually the work of trained scientists with experience as ichthyologists; the name must not be one that has already been used for any species in the same genus, and it cannot be the name of the person doing the naming. The first published name assigned to a new species has priority and remains the valid name with respect to the species; any subsequent species name given to the same species is invalid and may be termed a synonym once it is determined to be the same species. The species name is always the first name that was published for that species, and this name can only change under a few very strictly-enforced rules of the ICZN. The genus may change, sometimes many times, as the result of new scientific study. The Serpae Tetra for instance, Hyphessobrycon eques, has been assigned to five different genera since it was first described in 1882 by Steindachner as Cheirodon eques, but the species name “eques” never changes.
The genus name is either Greek or Latin, and is always capitalized; the species epithet is always Latinized and is never capitalized. The genus and species are in italics, followed by the name of the original describer of that species and the year in which it was named in standard uppercase. For example, Carnegiella marthae MEYERS 1927 tells us that this fish, the black-winged hatchetfish, was first described and named by Dr. George Meyers in 1927. When the describer and date are in parentheses, as for the Black Phantom Tetra Hyphessobrycon megalopterus (EIGENMANN, 1915), it indicates that the species is no longer in the genus to which this species was first assigned. In this example, Eigenmann originally placed this fish in the genus Megalamphodus but Stanley Weitzman and Lisa Palmer determined that the fish actually shares certain phylogenetic characteristics with the other species in the rosy tetra clade within the Hyphessobrycon genus, and in 1997 they published their findings and re-assigned the species to Hyphessobrycon. But as Eigenmann was the first to describe this fish as a new and distinct species, his choice of the species name remains valid and his own name as the describer is placed in parentheses.
The genus name quite often comes from some feature of the fish in that particular group; for example, the pencilfish are now all in the single genus Nannostomus, which comes from the Greek nanno (= small) and stomus (= mouth). When a scientist describing a new species recognizes that the fish has characteristics that are not common with the fish in all other existing genera, a new genus may be erected. The fish responsible for the establishment of a new genus is called the type species, which means that it has the special characteristics that will identify all future species within that genus.
The species epithet may denote some feature of the species, such as the false or green neon tetra, Paracheirodon simulans [= similar] in reference to the similarity in colour and pattern of this fish to Paracheirodon innesi [the neon tetra]; or it may honour the discoverer or another individual, as for example Hemigrammus bleheri named after Heiko Bleher who discovered the species; or it may refer to the location where it occurs, as for Corydoras guapore that inhabits the Rio Guapore system in South America.
The value of this binomial nomenclature system is certainty and clarity. Common names often differ even from one part of a country to another part, and certainly vary from one country to another, and are usually specific only to that language. In contrast, the scientific name can be used all over the world, in all languages, avoiding confusion and difficulties of translation. And it creates stability; though far from being absolute, the stability from initial name onwards is still an advantage for science and the hobbyist.
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