Growth Rates

[guppymonkey]

I have noticed some vast differences in growth rates between my various species of livebearers. My Heterandria formosa seem to grow very slowly. My goodeids start off large and seem to grow very quickly as well. Right now I have Xenotoca eiseni and C. pardalis and both seem to grow very quickly, doubling in size within a few months. The half beaks that I have seem to grow at a similarly quick rate. In comparison to some of the common livebearers like guppies, mollies and platies the rates of some of the rarer species seems to be much faster. Is this because of some of the rarer livebearing practices (such as in goodeids)?

 

[dwarfgourami]

Interesting. My portholes grow very quickly- according to Dawes they practise superfetation (I've been on holiday when most of them were born, so haven't been able to observe the birth). But then you say the heterandrias grow slowly- and they do superfetation too. Interesting. I am just about to order some phallichthys tico, so am hoping to gather more data soon.

 

[nmonks]

Very interesting. Might diet be a factor? Livebearer growth rate often seems linked to diet. With my Nomorhamphus halfbeaks, I noted an obvious jump in growth rare once they started taking daphnia, which I have in my pond in abundance. Their growth rate slowed down again after a few weeks though. Perhaps normal, or perhaps I wasn't able to supply daphnia fast enough for them.

Cheers,

Neale

 

[guppymonkey]

I haven't been able to supply myself with much actual living food. I usually use frozen or freeze dried live food along with a variety of pellet and flake foods. I know that there must be some loss in the freezing or freeze dry process. I wonder how much of a difference it makes. Can the impact of a pond vs a tank be factored? There must be some influence in growth rates from environment but I am not sure if it can truly be studied.

 

[nmonks]

I don't think what the food is makes the difference, I think it's abundance. In the wild larval fish (or newborn livebearers for that matter) will be feeding constantly on plankton and algae. In aquaria, we feed them 3 or 4 or whatever times per day. If you kept the breeding tank stocked up with live daphnia (for freshwater species) or live brine shrimp (for mollies in brackish) you could probably replicate this easily enough. You'd need a low power filter though; a simple sponge filter powered by air would be ideal. Also make sure there is algae in the tank, so the fish could feed on that, too.

Cheers,

Neale

 

[guppymonkey]

I don't think what the food is makes the difference, I think it's abundance. In the wild larval fish (or newborn livebearers for that matter) will be feeding constantly on plankton and algae. In aquaria, we feed them 3 or 4 or whatever times per day. If you kept the breeding tank stocked up with live daphnia (for freshwater species) or live brine shrimp (for mollies in brackish) you could probably replicate this easily enough. You'd need a low power filter though; a simple sponge filter powered by air would be ideal. Also make sure there is algae in the tank, so the fish could feed on that, too.

Cheers,

Neale

But if you lower the filtration how do you keep the water quality up? I usually do small water changes every day in my fry tanks but even with that the water quality can degrade very quickly with the amount of feeding going on. I don't really trust the filtration quality of sponge filters, they help keep the tank oxygenated but don't help with actually filtering the water especially in larger tanks.

 

[nmonks]

A sponge filter has a low throughput of water, yes, but it can support a very high population of filter bacteria, so it still does a good job of cleaning the water. Where air power filters fail is in [a] big tanks (lack of water circulation) and where there is a large biomass of fish to support. Multiple sponge filters could be used on, say, a 30 gallon tank holiding a brood of sailfin molly fry you wanted to grow on to around 3-4 cm before passing on.

I happen to use bubble-up box filters instead, but they work in much the same way, except are filled with filter wool. I can say from personal experience that a 10 gallon tank holding a brood of 15 halfbeak babies up to around 4 cm or so in length is well within the filtration capacity of a small box filter and a low-power air pump. Regular water changes are useful of course, and I always keep a few snails in the tank to mop up any uneaten food.

For me, when raising baby fish, the gentle water current far outweighs the disadvantages of air powered filters. I can keep the babies "swimming" in live food, and don't have to worry about small fish being sucked up by an electric pump.

Cheers,

Neale

 

[guppymonkey]

I haven't had to worry about my larger fry being sucked up by power filters. I breed mostly goodeids, my N. ebrardtii half beaks but I also have some small fish, Heterandria formosa. I haven't noticed any of these getting sucked up into the filter or even having problems with the current. I am using small tanks for most of these though so I am not sure if it would be a problem in tanks over 10 gallons. In the wild I would assume that even in the shallow water that most fry hide in there must be a current that is sometimes stronger than in my tanks. Not to seem critical of your methods of course. I guess its a case of multiple choices that could work.

Do you culture your own daphnia? I have thought of doing this but it seems like an involved time consuming process. I have done cultures of microworms for my tiny fry before but it is quite time consuming and smelly! I am trying all frozen and freeze dried foods now, though as you said it isn't quite the same feeding process as in the wild. I have seen continuous drip feeders for newly hatched brine shrimp feeding. Have you any experience with this? I was curious to see if it works easily.

 

[dwarfgourami]

Very interesting stuff, this; makes you think about how much you can do for your babies.
Going back to the original question, I would still have thought that the species has an important part to play. Am keeping guppy fry in a mature fry tank, where they get star treatment, extra water changes, fed several times a day, no competition for food etc. The portholes are in a cycled but not mature tank (so there would be less to eat), and get fed with the others twice a day, and there is a lot of competition from greedy adults. Guess which ones are growing the faster? The portholes are several weeks younger, but they already look and act like small adults, which the guppies do not. I have noticed with Ameca splendens fry that they also seem incredibly grown-up, when little.
The portholes were simply more developed at birth, faster swimmers, better at finding food. Other livebearer fry, I've been told, are born almost incapable of swimming and need a day or two to learn.
I'm sure you're right, Neale, and we can do a lot for our babies by feeding them properly. But I think Guppymonkey had a good point from the start and there is a difference between species, some naturally grow very quickly, others not so quickly. Perhaps in the wild there are benfits in both ways?

 

[nmonks]

dwarfgourami --

I think you misunderstand me. Of course different species grow at different rates. Humans grow more slowly than dogs, for example. I'm not aware of goodeids being across the board slower or faster than poecilids though, and how halfbeaks compare to the two, I don't know either.

But what I am saying is that environmental factors are probably very significant. A fast-growing species kept badly might well be overtaken in the speed stakes by as slow-growing species kept properly. Also, the bigger a fish is at birth, the easier it is to feed, so regardless of their potential growth rate, very small fry can be difficult to feed and hence do not grow as fast as they might. Consider two different species of livebearer where one set of fry needed newly-hatched brine shrimp but the other could simply take daphnia from the start.

guppymonkey --

To say I culture daphnia would be overdoing it. I have a plastic mock-barrel thing in the garden filled with leftover aquarium plants. Placed in some indirect sunshine. I took some water from the neighbour's pond, and let the daphnia do their thing. Also have some snails there, for the pufferfish. Simple, at least in summer. In winter, daphnia are still there, but they die back a bit.

Cheers,

Neale

 

[dwarfgourami]

dwarfgourami --

I think you misunderstand me. Of course different species grow at different rates. Humans grow more slowly than dogs, for example. I'm not aware of goodeids being across the board slower or faster than poecilids though, and how halfbeaks compare to the two, I don't know either.

But what I am saying is that environmental factors are probably very significant.

Absolutely. Lots of food for thought, so to speak, in your post. And what you say about growth rates related to size at birth makes perfect sense for the goodeids. There must be an awful lot you can eat if you are born as an Ameca splendens, say.

I am still interested in the differences between the species of the same family, why some small poeciliids are so "with it" from the moment they are born, while others seem...well...such babies. Is it different evolutionary stages? Different evolutionary benefits? Different ecological niches? Presumably, in the wild there would be a much wider range of even the tiny baby foods?

 

[nmonks]

I can't answer this directly, but I can throw a few ideas out here...

To start with, ask the question: why be a livebearer at all? Any given species wants to produce as many offspring as possible. Livebearers have far fewer babies than egg-layers, so on paper at least they are not as good. The explanation is of course that any one livebearer fry has a much higher chance of survival than, say, a single tetra fry. But in that case, why aren't all fish livebearers? Given livebearing has evolved multiple times, there's nothing "special" about it. The answer has to be that, most of the time, egg-laying is better than livebearing.

So, as a hypothesis, livebearing is favoured by evolution only in specific circumstances. While a "delicate" livebearer might seem to us as being a bit backward, presumably they are sufficiently ahead of egg-layer fry of the same age that evolution has favoured them. Perhaps where there are different livebearers competing, then the ones with the larger fry at birth have an advantage. But where there are only one or two species in a given river or lake, and all the competitors are egg-layers, then even "delicate" livebearers might be very competitive.

Cheers,

Neale

I am still interested in the differences between the species of the same family, why some small poeciliids are so "with it" from the moment they are born, while others seem...well...such babies. Is it different evolutionary stages? Different evolutionary benefits? Different ecological niches? Presumably, in the wild there would be a much wider range of even the tiny baby foods?

 

[dwarfgourami]

Oh Neale, this is just too interesting, you are totally ruining my day, I shall never get any work done at this rate! I am already behind with my article on Marcus Aurelius, and now I'm going to be thinking about biotopes all day instead.

 

[calum]

I.L.Y.P.

 

[nmonks]

You're writing about Marcus Aurelius? Very nice work if you can get it. I'm quite into Roman history... I started with Suetonius when I was a teenager and haven't looked back. Seriously, the more I learn about the Romans, the less surprises me about the modern world. It's all been done before. Anyway, I read one or two bits of Marcus Aurelius out at my dad's funeral. Okay, he's a little twee as far as philosophers go, but there's some very nice stuff there.

Cheers,

Neale