Tuesday, 23 March 2010

Marine aquaria and reef communities

New York Times has an article that looks at the effect of the growing popularity of marine aquaria on reef invertebrates. Unlike the freshwater aquarium trade, where captive-bred organisms dominate, the marine aquarium trade depends heavily on wild-caught fish and - more importantly, it would appear from this article - wild-caught inverts, which are important for maintaining the reef ecosystem. Since they play similar roles in nature as they do in the tank, overharvesting could have profound impacts on reef communities.

Saturday, 31 October 2009

Hybrid corys?

While I've heard reports of putative Corydoras hybrids, I have never seen any direct evidence of interspecific mating until this past week.

My main tank has a variety of corys - Corydoras panda, C. punctatus, C. arcuatus, C. aeneus, a probable C. trilineatus and another species whose identity I don't know. While I started off with several C. trilineatus, I only have one left. And apparently it's a female.

A few days ago, in a rainy week, one day after doing a water change, I noticed the trilineatus in the t-position that corys adopt while mating - with a panda. She then swam off grasping at least one egg (probably more) between her ventral fins.

While they clearly mated, I have no idea if the eggs would have been fertile. Regardless, I would be very surprised to find any fry. When she tried to place an egg, the rummynoses realised what she was doing, and proceeded to chase her around, hoping for some more eggs, I presume. Even though I tried to distract them by feeding them, the odds of eggs remaining unfound in that tank are probably pretty slim

Thursday, 17 September 2009

Ich update

It's been 10 days since my last post. I have long since reduced the temperature to normal and turned off the UV sterilisers. There's no evidence of ich on any of the fish. I'm inclined to think that the treatment worked.

One problem with this approach, I suppose, is that it permits the parasite to persist in the system. Fish that have recovered from ich acquire some degree of resistance. Reducing the temperature also slows the growth of the parasite. In combination this means that any residual infection would probably be difficult to detect. Ugh. Ironically, the best way to detect the parasite would be to introduce stressed fish that have not been exposed to ich. Unfortunately, that would equate to new fish from the pet store. And, in that case, there would be no way to determine whether they brought the infection with them, or whether they picked it up in my tank. I suppose the best thing to do is to observe the group of baby guppies that were born about a week ago. Not that guppies seem to be terribly susceptible...

Monday, 7 September 2009

Fighting ich

There are three places to buy freshwater aquarium fish in this town - Petsmart, Petco, and a local fish store. The LFS has friendly people and a much wider selection of fish. Unfortunately, they don't seem to quarantine their fish very well. I've had three ich outbreaks, and I believe that all of them have come from that store. Now, obvioulsy, I should have learned my lesson and made sure I quarantine all my new purchases. And for the most part, I've learned that lesson.

I recently bought a group of Otocinclus for my main tank. Many people consider them delicate fish which are hard to keep alive. My experience has been just the opposite - they strike me as almost bulletproof, great survivors. From what I've read, the main 'danger' period is just when they are introduced, because they are often very stressed in transit. Bearing that in mind, I decided to add them directly to my main tank. They seem to have settled in very nicely.

More recently I bought a group of fish from the LFS - corys, rummynose tetras, and three kuhli loaches. Given the difficulty in catching and moving kuhli loaches, I decided to take the chance and introduce them directly into my main tank. And the fun ensued.

Within a few days there were white spots on the rummynoses. I had successfully eradicated ich with salt and heat in the past, but the salt took a toll of some of my plants. I decided to try something different - a UV steriliser. When I went to the petstore, they were out of the 9V one I had my eye on, but they still had the 24V model. Now 9V sterilisers are recommended for tanks up to about 50 gallons (mine is 55), while 24V models are for tanks up to about 125 gallons. Wasn't too worried, since more power is probably better than less when trying something experimental. After I bought it, I poked around the web to see what people said about that approach. While people liked it for saltwater ich, there was a good deal of skepticism about its effectiveness for freshwater systems.

The next morning I looked at my fish and noticed that a lot of them had ich, far more than two days prior. I decided to play it safe and up the temperature. Then I hit the scientific literature.

Hitting the literature is often frustrating as an aquarist, since few papers are published on tropical aquarium fish. Fortunately, ich is a major problem for commercial aquaculturists. More so, in fact, in temperate than tropical conditions. From what I read, I realised that (a) a UV steriliser would probably do that job, and (b) heat alone would probably work as well.

Within two days of turning up the heat (three days of adding the UV steriliser) my fish were spot-free. It may be too early to say with certainty, but I feel pretty confident that it worked. And worked very well.

Friday, 28 November 2008


Six weeks ago I purchased a pair of albino Kribs (Pelvicachromis pulcher) - I've always wanted dwarf cichlids, and the new tank was in need of occupants that could handle "semi-aggressive" tankmates. (To be honest, while Macropodus are often described that way, mine have always been extremely gentle, inoffensive fish.)

Within a week the kribs started excavating a hole below a piece of driftwood. The female then started spending a lot of time beneath the driftwood. Cool, I thought, they are interested in mating. The second week passed, and the female spent a lot of time out of site. I didn't give it too much thought. Then at the start of week three I came home one day to notice both kribs were out on the open, keeping close to the bottom of the tank. As I looked a little closer I noticed movement beneath them and realised that they hadn't "considered" spawning, they had gone ahead and done so. Given that there were four large Macropodus in the tank with the kribs, I immediately became concerned for the safety of the fry. The kribs seemed to be attentive parents and the Macropdus had little interest in what went on at the bottom of the tank, but it still seemed only a matter of time until the krib fry turned into Macropodus snacks. It was thus quite a surprise when I realised that the kribs were quite effectively bullying fish that were 2-3 times their size. Even the (rather small) female krib was able to chase the Macropodus males off when they ventured too far down the water column.

Over the past three weeks the fry have grown remarkably quickly. Initially they foraged in a tight bunch on the bottom of the aquarium, attentively guarded by one parent (while the other parent patrolled the tank). As they got bigger they started moving away from the bottom, higher up the water column. On at least one occasion the parents seemed unsure what to do when half of the babies were on top of a piece of driftwood while the other half were foraging nearby on the bottom of the tank. Over the last week the fry have spread out and no longer forage as a group. They have also reached a size where they are no longer at much risk from the Macropodus - one of the fry ended up high enough in the water column that it attracted attention from one of the female Macropodus. She swam over to check it out, but then turned away. I'm guessing it was too big for her to consider it food.

Now what do I do with 20 kribs?

Friday, 15 August 2008


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...

Thursday, 14 August 2008

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.