Myths in Fishkeeping - Page 3: The Value of Biotopic Tanks

Myths in Fishkeeping - Page 3: The Value of Biotopic Tanks

Written by Marina Parha and George J. Reclos Tuesday, 16 September 2008 17:18

PDF | Print | E-mail

3. The Value of Biotopic Tanks

We want to create biotopic tanks because we want to offer our fish conditions similar or the same to those they live in their natural environments. This is supposed to enhance the fishes’ chances of survival in the aquarium as well as encourage natural behaviours such as reproduction.

The word ‘biotope’ is “derived from the Greek bios='life or organism' and topos='place'. So biotope is literally an area where life is living. More precisely, biotope is an area of uniform environmental conditions providing living place for a specific assemblage of plants and animals. Biotope is almost synonymous with the term habitat but while the subject of habitat is a species or a population, the subject of biotope is a biological community”.(16)

In turn a biological community is “a biocoenosis and describes all the interacting organisms living together in a specific habitat (or biotope). ….  The importance of the biocoenosis concept in ecology is its emphasis on the interrelationships between species living in a geographical area. These interactions are as important as the physical factors to which each species is adapted and responding. In a very real sense, it is the specific biological community or biocoenosis that is adapted to conditions that prevail in a given place.

Biotic communities may be of varying sizes, and larger ones may contain smaller ones. The interactions between species are especially evident in food or feeding relationships. Therefore, a practical method of delineating biotic communities is to map the food network to identify which species feed upon which others and then determine the system boundary as the one that can be drawn through the fewest consumption links relative to the number of species within the boundary.”(17)

These definitions highlight that the chemical, physical and other conditions which prevail in a biotope support a biotic community rather than a single species. This in turn indicates that specific water parameters may be immaterial or even slightly adverse for a particular genus of fish per se  but beneficial to it in that they favour or promote the growth of another member of its biotic community which is essential for the genus to survive (alimentation, for example). Hence, “nutrient availability … may influence growth forms of algae in ways that render them more or less susceptible to grazers. Ecologists need to scrutinize the mechanics of growth, grazing, and predation ….. These detailed studies, coupled with knowledge of the influence of factors like flow, temperature, light, nutrient availability, or population densities, will form a more solid basis for predicting responses of lotic communities to environmental change.”(18)

An interesting experiment supporting the case above is cited by Edwin Robinson and Menghe Li: “When raised in the laboratory under controlled conditions, a catfish can be induced to have a deficiency of a specific vitamin if it is fed a purified diet devoid of that vitamin. However, the same deficiency could not be induced in a pond raised catfish fed a practical diet lacking the vitamin in question. Thus, the vitamin requirement can be met either from vitamins naturally occurring in feedstuffs, natural food organisms, or from a combination of the two. Likewise, we have been unable to induce signs of mineral or essential fatty acid deficiencies in pondraised catfish fed diets containing no supplement”.(19) This indicates that particular environmental (i.e. biotopic) conditions which cannot be duplicated in the aquarium affect the fish only indirectly, in that they affect the organisms which the fish need to consume in order to survive and grow.

In this sense trying to imitate selectively conditions which may (or may actually not quite) exist in the natural habitat of a particular species seems to be pointless.(20) We most certainly don’t rely on the particular biological community where our fish originated from for their survival; in fact, most hobbyists will go to great lengths to suppress the development of any such community in their tanks.(21) Why should we be duplicating the conditions for such community to exist? Similarly, given the evidence that fish adapt to different conditions to the extent that fish belonging to the same species have occasionally different morphological characteristics and eat different types of food in the wild should we not be striving to create our own biotope in our aquarium, using what we have available?

We tested this idea in one of our tanks with considerable success. The tank is a standard 80 cm length - 106 L gross volume. We started without substrate; we placed some pieces of bogwood for the fish to hide under, three air filters and a couple of air stones connected to a blower, delivering approximately 600 l of air per hour. In this tank we introduced six L144 born on April 16, 2007, one Paretroplus damii born on May 10, 2007 and about eightyAncistrus sp. 3 born on May 23, 2007.(22) Initially the fish were fed five times daily; three feeds consisted of 100% pure spirulina powder and two feeds consisted of ten different commercial foods including Cyclopeeze which was grounded to a fine powder. Initially we changed 20% of the water daily gradually increasing to 50% to compensate for uneaten food and fish waste which was not removed. At this stage we also added a number of Planorbis corneus snails to deal with the food left overs and circulate the accumulating ‘substrate’. Ten days later, a layer consisting of fish waste and uneaten food was formed at the bottom of the tank and soon after life was established in it. First came red worms which mulptiplied rapidly at the beginning and then reached an equilibrium. By the third week the first insect larvae appeared in the substrate and were then seen in the water column. All the catfish were eagerly eating snail eggs, worms and insect larvae delving in the substrate while the cichlid was eating from the substrate as well as treating itself to free swimming larvae from the water column. At this point we reduced the feeds to three and then two daily; it was clear that all the fish preferred the live food present in their small biotope to the commercial one we were offering. A clear exception was spirulina powder which was always appreciated by the catfish. It soon became evident that the food we offered was eaten by the ‘live substrate’ and not the fish.

The growth rate of both the catfish and the cichlid living in this tank was impressive, especially when compared to their siblings kept in other tanks with ‘normal’ substrate and commercial food. The L144 reached a size of 5 to 7 cm TL in 3,5 months, the Ancistrus sp. 3 reached a size ranging from 4 to 5.5 cm in 2.5 months while the cichlid (renowned for being a slow grower) reached a TL of 3 cm in 3 months, with the brightest red dorsal fin we have seen in a Paretroplus damii fry. A rough estimate is that fish raised in this tank showed a 33% higher growth rate when compared to their siblings. The L144 had a bright yellow – orange coloration while the Ancistrus sp. 3 showed remarkable markings with a golden tint on their bodies. It was further observed that, despite the very large number of fish for an aquarium this size, all fish were well fed while the mortality rate was unbelievably low – one Ancistrus sp. 3 passed away when it was about 1 month old (less than 1,2%). All fish were always on the move, foraging for food. The cichlid developed extremely efficient techniques to capture the insect larvae; although he was on his own (i.e. without conspecifics) in this tank – something which is considered a no-no for fish of his species - he was very alert, never looked ‘bored’, swam around as if he had a purpose and showed the kind of energy one would expect for this species in the wild. Instead of waiting for the time the automated feeder will add food in their tank all fish actively searched for food day and night – unlike their siblings in the nearby tanks which have “learned” feeding times.

         

The effect of natural or “biotopic” parameters on a particular species which is part of that ecosystem is also of particular interest and merits some consideration. There is plenty of evidence to suggest that the conditions encountered in the natural habitat of an aquatic specimen could be far from ideal for it. Some years ago, we read an article by Diana Walstad, an author with a deep knowledge of aquatic ecosystems. She conducted an experiment to test the growth of aquatic plants in hard water. Three species which are found in soft, acidic water (Bacopa caroliniana, Saggitaria graminea and Ludwigia repens) and two species which are found in hard water in nature (Vallisneria spiralis and Bacopa monnieri) were all kept in hard alkaline water (pH=8) to evaluate their growth rate under conditions which were hostile for the first and favorable for the latter. To the surprise of Walstad (and ours), all plants did better in the hard alkaline conditions, their growth rate being at least double than the one observed in the water which was supposed to mimic their natural habitat.(23) One of them, Ludwigia repens didn’t even survive in the soft acidic conditions (which were supposed to be its “biotopic” conditions) but doubled in mass in hard water. Walstad concluded that “the explanation for this anomaly may be that softwater plants are found in soft water in nature, because that is the only habitat they can compete effectively against hardwater plants, many of which use bicarbonates [as a source of carbon] and can grow much faster”.(24)

Similar conclusions have also been reached about fish.(25) Let us assume for a minute that all fish originated in an environment which is favourable for them in a direct way. Some fish would naturally immigrate from this environment due to a variety of factors, such as predation or intraspecific competition. The fish that immigrate will find a new spot to colonise and adapt to, even if the biotopic conditions of this environment are less suitable for them since their primary task is survival. (26) If then fish are collected from these two spots with different parameters how are we to know which are the best (biotopic) parameters for these fish? Further, what evidence will we have if the first colony eventually perishes due to, say, predation or pollution and the only remaining colony is the one living in the less favourable environment? 

What does all that mean in practice? There is plenty of evidence to indicate that fish thrive and spawn in different environments. Naturally so; species with low, or no adaptability, are destined to perish mainly because a natural environment is a constantly changing environment. Hobbyists report repeated success in keeping and breeding different species of fish in considerably different conditions.  Hypancistrus, Corydoras, Betta, Trichogaster and so on are all fish successfully kept and bred in waters ranging, for example, from acidic to alcaline. This repeatability suggests strongly that the success indicated is not a lucky coincidence. It is evident that the “need” for a biotopic tank is at least questionable. We would suggest that hobbyists should devote more time, labour and money to improve hygiene and husbandry for their fish, instead of trying to replicate the impossible – and more often than not the unnecessary - a biotopic tank.  

Conclusions 

A biotopic tank is understood to be a simulation of a natural habitat. "Simulation" in this context can either mean a reproduction of the conditions of the natural habitat of a given species or an imitation of all or some of the conditions of such a habitat. If we understand simulation to mean the former then a biotopic tank is a contradiction in terms; it cannot exist, by definition, as it is impossible to recreate a given biotope in a tank. If, on the other hand, we understand simulation to mean the latter, then a biotopic tank is pointless.  The conditions we chose to recreate are random (usually determined by our very limited knowledge and our equally limited ability to achieve such recreation), causality is ignored and therefore the result is by no means closer to the natural habitat of the fish than any other environment that could have been created for them. 

Hobbyists invest a lot of time, money and effort to create "biotopic" tanks; it is worth considering alternatives which could be more beneficial to the fish and the hobbyist alike.