"Nuisance" snails, the facts

Byron

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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.​
 

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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.​
So, they can overrun the tank but aren't doing any harm in the process?
 

WhistlingBadger

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So, they can overrun the tank but aren't doing any harm in the process?
If they overrun the tank, it's because there are excess nutrients that are being processed by other organisms, anyway. So no, they aren't doing any harm, except perhaps to your tank aesthetics.
 

Uberhoust

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Because the aquarium is a close system we have nearly full control over the nutrients and energy entering the the system.

If we keep the excess energy and nutrients low we effectively control the amount of metabolic activity that can occur within the tank, and with that the waste materials produced.

Snails do not require as highly energetic and nutritious food as do fish and so can use the "food/poop" in the tank that is unavailable to the fish. This nutrient load is already in the tank, and will be broken down by other processes, so if we don't feed more because of the snails you are not adding any more to the metabolic potential within the tank.

This only will work if the fish are more active feeders than the snails so that the fish get the high quality foods, typically true. The snail population, feeding on the detritus, then becomes a coarse indicator as to how much excess nutrient load is in the aquarium. That being said snails added to a tank with an already high excess nutrient load may experience a population explosion followed by a population drop, this spike and crash can cause a number of issues with your cycle. A few dead snails in an aquarium can really cause the ammonia to rise. I have seen this happen so I don't entirely agree that a snail population explosion is benign.
 

AbbeysDad

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Any organism added to an aquarium that can/will break down organic matter will add to the biomass.
I see this differently in that snails, bacteria, fungi, ect. are digesting and converting organic waste so the conversion isn't really increasing or adding to the biomass...
Although some hobbyists seem to curse them, they serve a valuable function as members of the clean up crew.
 

Bruce Leyland-Jones

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I see this differently in that snails, bacteria, fungi, ect. are digesting and converting organic waste so the conversion isn't really increasing or adding to the biomass...
Although some hobbyists seem to curse them, they serve a valuable function as members of the clean up crew.
I've always considered 'biomass' to be the 'mass' of all of the biological componants in the tank...including snails and even the bacteria. Putting aside the bacteria, in its many and varied forms, I always struggle when people manage to convince themselves that snails don't count.
Surely, it is all relative?
To be sure, a few tiny ramshorn snails aren't going to have a huge impact and if your tank parameters can cascade into disaster as a consequence, then I'd suggest that the tank was a disaster waiting to happen anyways.
BUT...snails come in many types, behaviours and sizes and, as they grow, they can even compete with the fish for oxygen consumption and waste contribution.
 
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Byron

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I see this differently in that snails, bacteria, fungi, ect. are digesting and converting organic waste so the conversion isn't really increasing or adding to the biomass...
Although some hobbyists seem to curse them, they serve a valuable function as members of the clean up crew.

I tried to summarize Dr.Monks' information previously, so I may not have been all that clear when it comes to this aspect. @Bruce Leyland-Jones picked up on this too. 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.)​
 

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I've always considered 'biomass' to be the 'mass' of all of the biological componants in the tank...including snails and even the bacteria.
"Biomass is organic material made from plants and animals. Biomass contains stored energy from the sun. ... Some examples of biomass fuels are wood, crops, manure, and some garbage. When burned, the chemical energy in biomass is released as heat. If you have a fireplace, the wood you burn in it is a biomass fuel."
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An interpretation is that biomass is any/all living things so by their very existence in the tank, snails somewhat increase the biomass. But my remarks focused more on resulting waste... I once had a discussion with a Youtuber that had collected some snails in a container and seeing snail poo (waste), he concluded that the snails were increasing the waste bio-load in his tanks. To no avail I tried to convince him that the snails were not adding waste, but merely reprocessing existing waste further breaking it down. Now perhaps this is a somewhat over simplification, as for instance, in addition to other waste materials, snails will also consume algae and produce waste. But then this is a good thing!
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My point really was intended to point out that snails are actually very beneficial in spite of the fact that many hobbyists seem to find them offensive. I tend to find that for the most part, snail populations are self regulating based on the available 'food'... admitting that in a couple of my grow out tanks where the fry and young fish are well fed, there is a plethora of snails.... But the snails don't bother me or the fish, so I don't bother them! :)
 

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1 unit food -----> Bacteria (100%) -----> 1 unit waste (Adding food to an unpopulated tank results in rotting food generating waste through bacterial and fungal means)
1 unit food -----> Fish (50%) -----> Bacteria (50%) -----> 1 unit waste (Fish utilize the nutrients from the food faster but the waste is essentially the same)
1 unit food -----> Fish (50%) -----> Snails (25%) -----> Bacteria (25%) -----> 1 unit waste (snails consume the left overs from the fish, the waste gets produced faster but the amount stays the same)
1 unit food -----> Fish (50%) -----> Shrimp (20%) -----> Snails (15%) -----> Bacteria (15%) -----> 1 unit waste

Since the only source for nutrients is the food one adds to the fish tank each bit of food added has a corresponding amount of nitrogenous wastes that will eventually get produced. Obviously some nutrient gets used to create tissue and growth for the organisms but still the larger amount is simply used to keep the organisms functioning.

Fish having the higher metabolic rate use the higher quality higher energy food, but really cannot use 100% of the nutrients or energy from the food. Some creatures like shrimp have more efficient energy use and can use what the fish cannot. Snails have a slower metabolic rate and do not need as high energy food and can eat other organisms wastes. All are using some of the nutrient value from the food added to the tank.

The fish will use the energy they need from the food rapidly, the rest have to be happy with the left overs. The numbers are used to represent the amount of energy that each type of organism gets from the unit of food added to the tank, they are not an accurate representation.

This is the model I use. It is a model and there are exceptions but if you have a waste problem, the problem is you are feeding too much for the tank to keep up with. With this model you can add some "limited" numbers of additional creatures like snails to your tank without increasing the total amount of waste being produced. The snails do help with the decomposition of the waste food.

Personally, although snails are useful in the tank, I still don't like them. I own one Nerite snail that keeps the algae down in the QT.
 

Bruce Leyland-Jones

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1 unit food -----> Bacteria (100%) -----> 1 unit waste (Adding food to an unpopulated tank results in rotting food generating waste through bacterial and fungal means)
1 unit food -----> Fish (50%) -----> Bacteria (50%) -----> 1 unit waste (Fish utilize the nutrients from the food faster but the waste is essentially the same)
1 unit food -----> Fish (50%) -----> Snails (25%) -----> Bacteria (25%) -----> 1 unit waste (snails consume the left overs from the fish, the waste gets produced faster but the amount stays the same)
1 unit food -----> Fish (50%) -----> Shrimp (20%) -----> Snails (15%) -----> Bacteria (15%) -----> 1 unit waste

Since the only source for nutrients is the food one adds to the fish tank each bit of food added has a corresponding amount of nitrogenous wastes that will eventually get produced. Obviously some nutrient gets used to create tissue and growth for the organisms but still the larger amount is simply used to keep the organisms functioning.

Fish having the higher metabolic rate use the higher quality higher energy food, but really cannot use 100% of the nutrients or energy from the food. Some creatures like shrimp have more efficient energy use and can use what the fish cannot. Snails have a slower metabolic rate and do not need as high energy food and can eat other organisms wastes. All are using some of the nutrient value from the food added to the tank.

The fish will use the energy they need from the food rapidly, the rest have to be happy with the left overs. The numbers are used to represent the amount of energy that each type of organism gets from the unit of food added to the tank, they are not an accurate representation.

This is the model I use. It is a model and there are exceptions but if you have a waste problem, the problem is you are feeding too much for the tank to keep up with. With this model you can add some "limited" numbers of additional creatures like snails to your tank without increasing the total amount of waste being produced. The snails do help with the decomposition of the waste food.

Personally, although snails are useful in the tank, I still don't like them. I own one Nerite snail that keeps the algae down in the QT.
I hear you, BUT...

I acquired a population of physids and mini ramshorn snails when I only had plants in the tank...and the population of both of these has continued to grow without me adding food. This is in spite of me very carefully maintaining my plants, by removing any less-than-perfect leaves and so forth.
In order to cycle my tank, I've cultivated a range of necessary bacteria and whilst I wouldn't class these as food, excess or otherwise, I know the snails will munch accordingly.

Whilst I do appreciate that over-feeding of fish will result in excess waste and, as a consequence, excess snails, over-feeding is not always the reason for snail population growth and for the some people to repeatedly blame over-feeding as the cause for snail population explosions is over-simplification.
 

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