SPAWNING BEHAVIOUR.
Aquarists often go to great lengths to duplicate or at least reasonably simulate habitat conditions in the aquarium in order to stimulate spawning in their pet cichlids. It certainly helps, but one must not lose sight of the fact that these fish are often more adaptable than we give them credit for. A recent study on several Cichla species illustrates this point [6]. These fish spawn only once a year in natural habitat due to seasonality of the river flows. However, populations living in reservoirs spawn several times a year since they are no longer dependent on floodwater seasons, and they will do likewise in captivity.
To veer off topic a moment, aquarists may not realize how far in advance of professional ichthyologists they are in some respects, specifically with the ability to raise species at near or better than habitat conditions. This is something that some ichthyologists are just starting to notice [7]. The traditional problem is getting aquarists to publish what they have done, and more importantly, to accurately document in an objective manner what they did. Every aquarium club bulletin needs more articles, and what with exchanges and literature collectors, those articles have a wider dispersion than many over-modest authors may think.
PARENTAL BEHAVIOUR.
One reason why cichlids are so popular with aquarists is that they exhibit reasoned behaviours, as opposed to the average live bearer or cyprinid swimming blindly back and forth across the tank all day. Parental behaviour is where cichlids stand out. This is of interest to research scientists as well, not only from a strict behavioural point of view but also applied ecology, specifically the behaviour of introduced species. Florida’s environment has been damaged more than most areas in North America by introduced tropical fish because more species have a better chance of survival there, and because of the commercial fish farms supplying the aquarium trade. One study in Florida [1] considered that Tilapia mariae that has invaded communities previously dominated by native centrarchids, and also unfavourable areas such as channelized rivers. The success of T. mariae appears due to their specialized biparental care. One of the pair can defend the brood in its nest while the other patrols the borders against predators. They can also switch off while feeding, therefore always leaving one parent to protect the fry. The male and female of a pair co-ordinate their actions with each other, thereby improving the survival rate of their young.
Although biparental care is common enough in substrate-spawning species that keep the eggs or young in nests, it is quite rare in mouthbrooders. Out of about 1,000 species of mouthbrooding cichlids, only about 35 have biparental care [5]. The reason seems fairly obvious, for if the fry or eggs are sheltered in one parent’s buccal pouch, then the help of the second parent is not really needed. The 35 species, such as the Tanganyikan Eretmodus cyanostictus, are in the transitional stage between the substrate spawners who provide biparental care and the uniparental mouthbrooders.
Aquarists will often observe parental cichlids fanning their brood. At the egg stage this can be attributed to increasing oxygen flow and sweeping away debris. Once the eggs have hatched, parents may often begin brushing the substrate with their fins. This fin digging behaviour stirs up microscopic life from the substrate for the fry to feed on [4]. In Cichlasoma octofasciatum, for example, as the brood ages from 3 days after hatch to 10 days after hatch, fin digging increases. By the way this is where aquarists can make a difference. Professional ichthyologists can only study a few species of fish; most of their time is taken up by teaching and paperwork. Aquarists will see far more species than the average university professor ever will, and should take advantage of that to study them and report in print the results. While it is true that the average aquarium does not provide a suitable simulation of habitat for release of natural behaviour, it is still the case that any kind of documented observation may come in useful. What is important is for the aquarist to note cichlid behaviour objectively, such as life stage, how many days, and what the aquarium was like.
FEEDING BEHAVIOUR.
Cichlids often lose favour with aquarists because they exhibit aggressive behaviour, as opposed to the average live bearer or cyprinid swimming blindly back and forth across the tank all day. Much of this aggressiveness is more supposed than real, as most aquaria are too small to allow cichlids room to escape unharmed or stake out proper territories. This is one of the reasons for the time-honoured advice about always buying the biggest tank you can reasonably afford (the other reason is that larger volumes of water have more stable chemistry).
Cichlid aggressiveness is partly based on protecting feeding territory. It has been demonstrated that cichlids are more aggressive to other fish that have the same feeding habits [3]. Those that feed on a different food source will be tolerated and allowed to co-exist. A mbuna that picks only at algae-covered rocks is not particularly concerned to see another species of cichlid munching on something it snagged in mid-water. This assumes, of course, that space is not a limiting factor for the cichlids, as so commonly it is in the home aquarium. In an ideal world, no aquarist would buy an unknown (to them) species of fish in a pet store. They would have read up on the fish prior to entering the store, have a tank prepared at home, know what kind of food to give them, and how to present the food to them. In the real world, of course, most of us have been guilty of succumbing to impulse and buying something we hadn’t expected to. In fairness, pet stores often receive ‘contaminant’ species mixed in with their orders, and if the aquarist doesn’t buy then on the spot, the opportunity will be lost by the time of a return visit.
Bringing home a new and unknown fish presents problems in how to care for it. Your reference book may not list that species. If so, how and what do you feed it? Experienced aquarists know that the preferred diet and presentation of a fish can be guessed quite accurately by studying its eyes and mouth in particular. This has been confirmed by scientific studies. Detritivores, or bottom feeders, usually have their eyes high up near the top or dorsal position of their bodies, so they can see while plowing the substrate. Piscivores, who prey on other fish, have large, often extensible mouths. Surface feeders have their mouths turned up to the water surface. Midwater fish have their eyes on the sides of their heads to give a better all-around view of the water for both prey and predators [2]. By studying your new fish purchase, you can therefore tell whether you should be feeding them floating flakes or sinking pellets.
REFERENCES.
1] Annett, C.A., R. Pierotti, and J.R. Baylis (1999) Male and female parental roles in the monogamous cichlid, Tilapia mariae, introduced in Florida. ENVIRONMENTAL BIOLOGY OF FISHES 54:283-293
2] Hugueny, B. and M. Pouilly (1999) Morphological correlates of diet in an assemblage of West African freshwater fishes. JOURNAL OF FISH BIOLOGY 54:1310-1325
3] Genner, M.J., G.F. Turner, and S.J. Hawkins (1999) resource control by territorial male cichlid fish in Lake Malawi. JOURNAL OF ANIMAL ECOLOGY 68:522-529
4] Zworykin, D.D. (1998) Parental fin digging by Cichlasoma octofasciatum (Teleostei: Cichlidae) and the effect of parents’ satiation state on brood provisioning. ETHOLOGY 104:771-779
5] Neat, F.C. and S. Balshine-Earn (1999) A field survey of the breeding habits of Eretmodus cyanostictus, a biparental mouthbrooding cichlid in Lake Tanganyika. ENVIRONMENTAL BIOLOGY OF FISHES 55:333-338
6] Jepsen, D.B., K.O. Winemiller, D.C. Taphorn, and D.R. Olarte (1999) Age structure and growth of peacock cichlids from rivers and reservoirs of Venezuela. JOURNAL OF FISH BIOLOGY 55:433-450
7] Carlson, B.A. (1999) Organism responses to rapid change: What aquaria tell us about nature. AMERICAN ZOOLOGIST 39:44-55 ?