Stocking

At some point, every aquarist has ask the question "how many fish should I put in my aquarium?" Conventional wisdom says "one inch of fish per gallon". Earlier this year I blogged about two articles that challenged that dogma, one in Practical Fishkeeping and the other in Tropical Fish Hobbyist. In each case, they suggested that a well-established tank could support twice that level - two inches of fish per gallon.

While territoriality and aggression can play into the number of fish you can keep in a tank, those are species specific considerations that overly any basic rule of thumb. Far more basic is the issue of oxygen supply. While certain fish depend on gaseous oxygen (the best known being the anabantoids), most fish depend on dissolved oxygen. Too many fish and too little surface area will lead to problems. The other issue is "bioload" - the production of waste products by the fish. These include nitrogenous compounds and organic waste. Ammonia and nitrites are harmful at relatively low concentrations; they tend to be a problem in new tanks, but can also build up in established tanks if the biofiltration crashes. Chances are though, if the biofilter crashes, even a moderately stocked tank will run into major problems. Nitrates, on the other hand, are only a problem at higher concentrations, but unlike ammonia and nitrites, they are not broken down by most biofilters. Organics are a separate issue - one that doesn't seem to get all that much attention. Some people specifically add organics ("black water extract") to their tanks. Others stress the importance of water changes to control the levels of organics. The simple truth is that there are a whole host of organic compounds, and their effects on fish are going to vary.

Bearing all this in mind, and the fact that "inches per gallon" is a very crude rule of thumb (more on that later), I sat down and assessed stocking in my main tank this morning. It was an interesting exercise - based on the "inch per gallon" rule, my tank is slightly overstocked. Of course, that involves weighing a 3.5-inch kuhli loach as placing a greater demand on the system than a 3-inch Macropodus (which probably has more than twice the body mass, but almost no dissolved oxygen demand). If I chose to follow the "two inches per gallon" rule, I could almost double the stock of fish in my tank. Right now, that seems reasonable - the upper two thirds of the tanke are currently occupied by three fish; everyone else is near the bottom of the tank (and largely hidden by the plants). Things looked different this morning just after I fed the fish - in the flurry of activity, the tank seemed to have twice as many fish as it does now.

Aside from the obvious issues of filtration and water changes, I think there are two main things to think about when it comes to stocking - the space available, and the overall ecology of the tank. The main tank tends to have higher nitrate levels than either of the small tanks. This is largely a function of the amount of plant biomass - the other tanks are choked with plants, which presumably consume any available nitrogen. The main tank, on the other hand, has far less plant biomass (though this may change). Increasing the plant biomass probably increases the overall number of fish the tank can support. The other issue is one of space. Where in the water column does a fish live? Recommendations for cory stocking seem to be expressed in terms of tank surface area - or actually, the area of the base of the tank. (Is this modified by having a more heterogeneous tank bottom?) In my main tank, the open water is only used by the Macropodus. The corys spend their time on the bottom of the tank, with occasional forays up and down the plants. The Glowlight tetras tend to swim among the plants, while the Rummynose like the open water in front of the plants - they rarely venture above the level of the taller plants. (I suspect that as the plants get taller, they will expand their usage). So in terms of fish to add, the obvious choice would be an open-water species (zebra danios are what come to mind) or a surface species (guppies or some other small live bearer?) That is, of course, if I decided to trust the two-inches-per-gallon rule of thumb...

Tank talk and lighting options

As often happens, I went through a period of neglecting my tanks, especially my (55-gallon) main tank. It's the kind of thing that happens to almost every aquarist at some point in time. The main tank has always been light-deficient - while most people recommend 2-3 watts per gallon* for a planted tank, my plants were forced to get by with approximately 0.55 watts per gallon. As long as I was feeding them Flourish Excel, the plants seemed happy (especially the Cambomba), but once I quit, only the Java fern and Echinodorus ("Amazon swords") did much.

While the main tank was suffering a lack of plant growth (somewhat masked by the expanding Java ferns), my other tanks were experiencing the opposite problem - too much plant growth. The plant tank was covered by an emergent carpet of Ludwigia and Bacopa monnieri; the tank itself had turned into a mass of roots. The Otocinclus tank was similarly overgrown, although instead of being covered by emergents, it was covered by a think layer of floating plants.

At the end of July I shook myself out of my torpor and started moving plants from the plant tank to the main tank. I realised that I had to upgrade my lighting, but at that point in time, it just wasn't an option. I replanted a lot of Ludwigia and a little Bacopa into the main tank, and cleaned up the mass of floating vegetation (I either replanted the stuff, or got rid of it). And then I had to leave it all alone for a week and a half.

One of the main reasons I wanted to clean out the plant tank was the fact that we would be gone for a while. I don't have a timer on that tank, so I have just left the lights on when we are gone. One time I returned to find the tank a thick mass of hair algae - so thick, in fact, that the water was obviously not circulating (some areas were very warm, others were far too cold). While that is likely to be less of a problem in summer, I still wanted to clear out enough vegetation to give it some room to grow. But moving plants to the main tank created a problem - did I really want to go to all that effort, and then watch the plants turn into spindly things before slowly dying? While a lighting upgrade was in order, I had neither the time nor the money for anything of the sort.

On the way home from Michigan I finally stopped into Preuss Pets in Lansing, Michigan. A friend of mine has been saying great things about them for years, all the more now that they have moved to a larger place (more later). I ended up buying a really nice new lighting system, and I now have two 54 watt bulbs on the tank. Not too surprisingly, the change was remarkable. I have also continued to move plants from the plant tank to the main tank. It's too early to say home much of it will really take (a lot of what I transplanted was emergent in the old tank, so it will have to adapt to being submerged), but the tank looks great and the fish seem happy, poking around in the new vegetation.

* It's actually more complicated than simply "watts per gallon" - not only does the light output matter (not all 30-watt fluorescent bulbs are the same), it also matters what wavelengths the bulbs produce.

Baby Corys?

A while ago I tried to convince my pygmy corys to breed, but without much luck. Water changes (especially in coincidence with weather fronts) could get them to come out and "dance". Recently I have noticed more complex behaviour, including what looked a bit like the "classic-T" behaviour that spawning corys adopt. But I had pretty much given up hope of anything actually happening.

Last night I noticed something moving at the front of the tank. Before it darted back into the thicket of Hemianthis I saw something that looked like a tiny tadpole, maybe 4-5 mm long. It took me a moment to realise what I had seen - fry! Over the next couple hours I caught another glimpse of it. Very cool!

Now, I can't say for certain that it actually was a baby cory - there are also a few Otocinclus in the tank, but odds are that it was a pygmy cory. Pygmy corys are considered easy to breed, while Otos are rather less easy. Also both fish are easier to breed in groups - I had 7-10 corys in the tank, but only three Otos (and one, I suspect, is a different species from the other two).

Bugmeal?

While I have read some of the people at ScienceBlogs on a daily basis for months, I still have not plumbed the depths of what’s available in terms of good reading. I recently came across Shifting Baselines, a good ecology/conservation biology blog written by Jennifer Jacquet, a doctoral student at the University of British Columbia, Josh Donlan, a conservation scientist at Cornell and Randy Olson, the creator of A Flock of Dodos.

In January, Jacquet discussed a study which looked at replacing fishmeal (which is used to feed chickens, pigs and fish) with “bugmeal”. Working with striped bass, researchers at Mississippi State University found that the fish readily took the “bugmeal” and the final product was similar to fishmeal raised fish, but had a less “fishy” smell (which is considered a bonus by American consumers). Today she presented some response to questions she asked Lou D’Abramo, the lead scientist on the Mississippi State project.

The first question really gets to the heart of the problem of our industrial food production system: what are the insects raised on? The answer - grain, probably corn. Lovely. Fortunately, D’Abramo seems to be aware of the problem with that, and discussed the idea of raising them on fish wastes. He also talked about raising insects on waste products to alter their fatty acid profile - something that wouldn’t have have been the least bit surprising had I read that with my aquarist brain switched on…you read a lot about fatty acid profiles in the context of getting your Corydoras to breed. (I should do a less good job of compartmentalisation.)

Finding a substitute for fish meal is a good thing. Insects sound like a good substitute. But our industrial system of agriculture just makes things like this awfully complicated - needlessly complicated. Small farmers feeding fish on grubs or mealworms raised on locally generated waste sounds workable. Industrial-scale “bugmeal” production, on the other hand, raises the usual problems of energy demands, transport, and waste production. One step forward, but we’re on a conveyor belt running us backward…

Otocinclus notes

Otocinclus, the dwarf suckermouth catfish, is a very popular algae-eating catfish. The seventeen species of Otocinclus (often called Otos) are very popular for algae control. Unlike their large cousins, the Plecos, Otos remain small and are not boisterous enough to cause damage to plants. Although they are often purchased singly for algae control, Otos are social and should not be kept in groups of less than three. They are native to South America east of the Andes mountains, in streams that drain into the Amazon, Orinoco, Paraguay/Parana rivers, and in streams that drain into the Atlantic in southeastern Brazil. They are notably absent from the Guianas.

Otos are small - they range in size from 16.5 to 43.8 mm (0.6 to 1.7 inches), not counting the tail. Females are 10-20% larger than males, and have a broader body, especially when they are in breeding condition. [Read the rest of my post at HubPages.com]

Corydoras notes

With 150 formally described species, and perhaps more than a hundred undescribed species, the genus Corydoras offers great possibilities for fish keepers. All species are easy to keep, relatively undemanding fish with great personality. Many of them are readily bred. For the average fish keeper they are relegated to the "cleanup crew" and kept singly or in very small groups. Even under those conditions, they can be interesting fish. Kept in larger groups, they really shine and can become the focal point of a lively aquarium.

Corydoras are social fish - they should not be kept in groups of less than three. They appear to be happiest in groups of six or more. With the right selection of fish and appropriate aquascaping you can enjoy almost constant activity as they swim around a community tank. [Read the rest of my post at HubPages.com]

Snails in aquaria

Snails are nearly ubiquitous in freshwater aquaria. Aquarists vary in their attitude towards snails - many see them as a scourge that must be controlled, if not eliminated outright. Bulletin boards are full of questions about how to control snail populations. Snails are easily introduced on plants, rocks or other decorative items like driftwood. Most reproduce quickly and some, like Malaysian Trumpet Snails, quickly grow to the level of infestation. Some snails eat plants, and can damage aquarium plants. Some will eat eggs, even baby fish. And some play a role in the life cycle of fish pathogens.
Many aquarists seem snails in a more positive light. Snails consume algae and can keep glass and rocks clean. Snails consume dead plant parts and uneaten food that might otherwise decompose and foul the water. Trumpet snails burrow through the substrate and bring oxygen into these substrates.
Quite apart from this utilitarian view of snails, some aquarists see them as desirable pets, and may dedicate aquaria to certain species. Popular pets include Olive Nerita snails, Ramshorn snails and Apple snails (also known as Mystery snails). [Read the rest of my post at HubPages.com]

Pygmy corys

They say that pygmy corys (Corydoras pygmaeus) are easy to breed. That is, of course, a relative statement. "Easy" relative to what? But at this point, doing so is one of my primary goals.

In general, in order to breed corys you need frequent water changes coupled with a "conditioning" diet. They conditioning diet is a rich diet - often with a lot of live food, and essential fatty acids - that bring the fish into breeding condition. Water changes, on the other hand, mimic the beginning of the wet season, when streams and pools get an influx of fresh water. Fresh water, often cooler (although people have said that "cooler" is not important for pygmy corys).

The tank the corys are in is open-topped. As a result of this, evapouration rates are high. Over the last several months, this has meant that I am more inclined to add water than I am to exchange water. Presumably that resulted in very hard water - not the optimum for these fish. So over the past few weeks I concentrated on getting the water closer to tap water, but doing frequent, large water changes. Over the last week I have tried to soften the water some more by adding reverse osmosis water.

The pygmy corys have responded fairly well to the water changes - they seem much more active the past few days, although they still spend most of their time hidden below the dense lawn of Hemianthus. I'm cautiously optimistic.

Otocinclus tank

It's been almost a month since I re-did the former Macropodus tank. After I cleaned the tank out and added some new plants, the old plants died back seriously. It was especially noticeable with the Echinodorus, which had previously dominated the tank. Their leaves first went pale, and then much of the tissue died, but not the whole leaf.

Apart from adding a lot more plants, I also created a small "sand lens" in the front of the tank. And, of course, I added a population of Otocinclus and two dwarf corys. So how have things changed?

Here's the tank today; while I'm having a hard time getting the Lilaeopsis to root, the Hemianthis is really coming along nicely.

Here's the tank three weeks ago, when the die-back had just started


And here's the tank three days before that, shortly after I had cleaned it out

Using biogeography to guess at species identity

Just over a week ago, I found two Corydoras habrosus mixed in with the Otocinclus at the local Petsmart. Since C. habrosus is restricted to the Amazon basin, it struck me as a useful clue in trying to identify the Otos. In his 1993 monograph on the genus Otocinclus, Scott Schaeffer mentions that only two species of Otocinclus are found in the Orinoco basin - O. vittatus and O. huaorani. I'm leaning a little more towards O. vittatus, but I really need to take a better look at them.

Shape or colour? It depends on where you grew up

Dave Munger at Cognitive Daily reports on a study of how the environment in which fish are raised affects their spatial perception and memory. Convict cichlids raised in square tanks used shape and colour to navigate, while ones raised in round tanks relied on colour more than shape.

Diversity in Malawi cichlids

Ed Yong has an excellent discussion of the way in which male aggression contributes to species diversity in Lake Malawi cichlids. While a number of factors were involved in the rise of this species flock, the tendency for males to be more aggressive towards males that look like them is likely to be one of the factors that drives speciation.

Questions?

Judging by the Google searches that bring them here, a lot of people who find there way here are looking for the answer to a specific question...answers that my posts often don't provide. If you have questions - feel free to ask. I can't make and promises, but I'll give you the best answer I can.

Otocinclus tank

While many aquarists value Otocinclus catfish as algae eaters, they seems to be looked on more as a part of the tank maintenance system than as "pet fish". And quite frankly, my impression of them was that they just weren't the most exciting fish. While I found them interesting, they never seemed to do much. So I was intrigued by an article in the February issue of Tropical Fish Hobbyist by Gary MacDonald. Not only did he say that they are very social fish, he also spoke of interesting dominance hierarchies in groups of 12 or more. While this caught my attention, I didn't feel like I had room for another dozen or so fish in my main tank. With the former Macropodus tank available, I ended up buying some, pretty much on a whim.

From what I've read, one of the major concerns about pet store Otocinclus is that they are often starving - they are herbivores, and are likely not to have had enough to eat for a while. There is also the stress involved in being caught and transported home. Once I got them into their tank, they all went for the bottom or the sides of the tank and just suck there. But after a few hours they were extremely active, swimming all around the tank, presumably examining surfaces for algae. They have slowed down a little since then, but they remain much more active that any Otocinclus I have seen previously. Of course, they are also very young - I wouldn't be surprised is they slowed down a lot as they matured. It'll be interesting to see what happens.

The great cory hunt

After finding a pair of Corydoras habrosus at a local Petsmart, I saw this post at PlanetCatfish - the poster had received a C. habrosus in a group of Otocinclus, presumably in Missouri. That got me thinking - since all the local Petsmarts presumably get their fish from the same source, maybe there were more C. habrosus at other local Petsmarts. So we decided to go on a cory hunt. We visited four of the seven Petsmart stores in the Oklahoma City metro.

We failed to find any more C. habrosus, but it was fun to try.

Tank shots

In the past couple days I added more plants to the tank, trying to create something of a thought-out aquascape (or at least something that could be thought of as something like a thought-out aquascape. Here's how it looked three days agoI added Hemianthis, Lilaeopsis and some Vallisneria to the forground, and planted a number of stems of Cabomba along the back, in front of the heater. I also added some Ludwigia along the centre, to add some more dimension. This is the way it looks now

New fish

For no reason in particular, I visited our local Petsmart today, and was rewarded with a rare treat - in a tank of Otocinclus there were two dwarf corys - not pygmaeus, but I knew it must by one of the others. It turned out to be Corydoras habrosus, a Venezuelan species.

That pretty much decided the fate of the former Macropodus tank. I couldn't put the new corys into the main tank (they're a bit small to cohabitate with adult Macropodus), and I didn't want to add them to the plant tank without quarantining them first. So that left the former Macropodus tank. And since I didn't want to leave them as the sole occupants of the tank, I took the opportunity to buy a dozen Otocinclus, as Gary had recommended.

New cyprinid genus

A new genus of cyprinids, Hongshuia was described in China recently to accommodate two new species, Hongshuia paoli and H. banmo, which have been described from the Pearl River system in Guangxi Province in South China.

Source: Practical Fishkeeping.

Display tank or breeder?

As I mentioned previously, I now have an available tank to stock. The first step was cleaning it up - the tank was badly overgrown and the substrate was very dirty. Over the course of cleaning it took 10 or 15 gallons of water out of a 10-gallon tank - and even then, I didn't get the substrate completely clean.I took out most of the Rotala - it just hadn't taken very well in that tank. I also pruned the Echinodorus plant rather severely - that should let more light through. I may need to add some more plants to the foreground, from the perspective of a "planted tank" it has a major deficiency - the lack of adequate substrate. The tank has nothing but rather garish red and black gravel. In the course of cleaning it up, I took most of the organic material out of the substrate, thus removing most of its nutrient-holding capability.Now I need to figure out what to do with this tank. Do I want to give the corys a chance to breed? Having done so much to make the tank pretty, do I really want to turn it into a breeder? Or to put it differently - can I make a breeding tank visually interesting? If I had a few more pandas I could make a little shoal of them...but the reason I want to breed pandas is my lack of pandas.

Hints for beginners

In an article published today on Practical Fishkeeping's website, Karen Youngs has some good advice for new (and not so new) fish keepers. Some of it is obvious to anyone who has done some reading, but other things were new to me.

Her first word of advice is not to stock tanks too quickly - wait for them to cycle. When I first kept fish, back around 1980, I was unaware of the concept. I don't recall it being in any of my fish books. When I returned to the hobby last year, it was something I was made aware of almost immediately - quite rightly, it's one of the first things they tell you are the pet store. That said, I still messed up with the whole cycling thing - it would have saved me (and my platies) a lot of stress if I had understood the time course a little better. I had fin rot and "shimmying" fish - because the tank wasn't yet cycled. While everyone wants fish as soon as possible, fishless cycling is much less stressful on the aquarist. But who really knows that right when they start off?

Once you have a tank that has cycled, you still need to add new fish slowly. More fish means a larger input of nitrogenous compounds. Since the bacterial populations will be limited by food availability, adding too many fish too quickly, even to an established tank, can cause a spike in ammonia or nitrite levels.

Her next piece of advice seems pretty straightforward as well - don't overfeed. But overfeeding is an elusive idea. If you read a pack of fish food they will say "no more than the fish can consume in three minutes". But that really depends on the fish. Some fish will take a couple minutes to even notice the food. Others will just keep eating. If I could get flakes that would float for three minutes, I suspect that my Macropodus would consume their own body weight in food.

Youngs has some interesting advice about feeding that I hadn't come across before. "How often should I feed my fish?" is a common question. Some people say three times a day, some people say once a day or less. Why such diversity of answers? Probably because it depends on the fish you're keeping. Youngs advises feeding small fish like tetras and guppies several times through the day. Larger fish should be fed less frequently. In addition, herbivores need to eat more often than carnivores. This is all pretty obvious once you think it through, and it's probably something a lot of people know intuitively. But again, it isn't something I remember coming across before.

She has some fairly standard things to say about lighting and algae, but again, says them well. Good advice on acclimating your fish, and on suitable tank mates. She advises redundancy when it comes to heating and filtration - two filters, two small heaters. Why small heaters? Because if one sticks on the "on" position, it won't heat the tank up too quickly. Common sense. Hadn't thought of it.

The last point she makes has to do with stocking levels. If you visit discussion boards, most people talk about the 1 inch per gallon rule as the upper level when it comes to stocking, which is why I was surprised when I read that an article in the February issue of Tropical Fish Hobbyist which suggested that you start a 10-gallon tank with "10 neon tetra-sized fish" (1 inch per gallon) but that you could eventually go to double that once your tank was well-established. Bending the rule a little - I'm sure most people do that. But going to double that? I was surprised. So it was nice to see Karen Youngs give similar advice

Nowadays with better filtration it is hard to give an exact figure, but PFK recommend the following:

Tropicals: 1” per gal/ 2.5 cm per 4.55 l initially, then up to a maximum of 2” per gal/5 cm per 4.55 l after six months.
Coldwater: 1” per gal/2.5 cm per 4.55 l.
Marines (fish and inverts):
1” per 4 gal/2.5 cm per 18 l.
Marines (fish only): 1” per
2 gal/2.5 cm per 9 l.
Ponds: 10” per 100 gal/25 cm per 455 l.

Getting that sort of advice from one source seemed iffy to me. Getting it from a second, independent source (and getting a more nuanced answer) makes me feel a little more inclined to integrate that factoid to my pool of knowledge.