Pet Care Tips, Advice and Information

For fish to breed successfully in the aquarium, they must be healthy and feel that all conditions are right. Generally, it is difficult to breed fish caught in the wild, as they are much more demanding in their requirements, but usually even the most awkward types can be bred by expert aquarists. After the first few generations have been bred, further breeding is progressively less difficult, as the ‘easy breeders’ become selected out from the population. Thus fish which, when first imported, commanded very high prices become quite cheap once the principles of breeding have been mastered. For example, the Neon and the Cardinal were originally very expensive and bred only — and with great difficulty — by the specialist, but now both are standard aquarium fishes, available everywhere at moderate prices, and easily bred.

Among the species which cannot be bred easily are those which become very large, and in which only the immature fish are kept in the aquarium. Some African Catfish fall into this category, as do many marine fish. Usually, however, breeding can be accomplished once the environment and biology of the fish are com-politely understood.

One curious factor in breeding is that, although the breeder can often select out natural mutations with unusual colors or long trailing fins, and develop new strains, sometimes the general quality deteriorates in captivity. For example, it is seldom possible to preserve the huge dorsal fin on the Sail fin molly or the bright colors of the Cichlid Apistogramma Ramirezi when these fish re-bred in captivity. Wild stock is larger, more robust and more brightly colored.

Breeding considerations have given rise to much of the into-resting behavior of fish. Even coloring can be traced back to breeding needs. Often male and female fish are colored quite differently, and male fish may be brightly colored both to attract females and to frighten off rival males.

Most fish do not breed continually. The experienced eye can pick out fish which are pairing off as they reach peak condition for breeding. The sides of the fish fill out, and females, packed with eggs, become especially plump. Coloring becomes generally more intense, and males may display to the females with rigidly out-stretched fins. When spawning is imminent, there is often change in the fishes’ behavior: they tend to become very active and to explore possible spawning sites.

The sexual organs of fish are relatively simple, consisting of paired, elongated organs lying along the abdominal cavity — these organs produce either eggs or sperm (milt). Nearly all fish shed both eggs and milt together into the water, where fertilization takes place. However, a few are live-bearers; that is, the male introduces his milt into the female, who retains the fertilized eggs and gives birth to live young. The Guppy is the best known of these fish.

Fish eggs are thin-walled and delicate, and are eaten greedily by most species, many consuming even their own spawn. Various special techniques have been evolved to ensure the survival offices’ eggs — or, at least, of enough of them to ensure the continuation of the species. Indeed, the method evolved by most fishes into produce such huge quantities of eggs that some are bound to survive. These egg-caterers are usually shoaling fish, which spawn in a group. Our common river fish are of this type, and so are their exotic relatives which are kept in the aquarium. Fishes like Barbs, Dasios and Razors all scatter their eggs among plants. Sometimes the eggs are sticky, and become attached to the plants; others simply drop to the bottom. The spawning fish and others promptly eat as many of the eggs as they can find, but some will normally survive, hidden among the leaves of plants or in cracks between the gravel.

In the aquarium, the survival rate can be improved by using breeding tank. The parent fish are placed in the tank when ready to breed, and removed as soon as spawning is complete, so that theory can be safely raised. The type of breeding tank used depends on the type of fish involved. For fish which naturally spawn on gravel it is usual to cover the tank bottom with glass marbles or glass rods: scattered eggs fall between the marbles or rods, and the parent fish are unable to reach them.

A slightly different set-up is needed for fish which spawn among plants. You can place fine-leaved plants like Myriophyllum in the breeding tank but, although these may look more natural to us, fish do not discriminate between them and the more hygienic option, a bunch of nylon wool, which will not carry any disease organisms to attack the eggs or fry. Spawning fish will dive with equal enthusiasm into either plants or wool tufts to deposit their eggs.

Not all fish are such profligate egg-caterers. Egg-laying tooth-carps attach their eggs individually or in clusters to the plants. As would be expected, more eggs survive so fewer need be laid. Other members of the same group bury their eggs, diving down into themed on the pool bottom and releasing their spawn. Here it is pro-tested from predators and can survive for long periods — even if the water dries up completely. For some species, the drying-up inessential, and eggs will hatch only after a prolonged period of drying followed by normal aquatic conditions. Since these are the conditions they experience in their normal habitat, the breeder must imitate them.

Many fish look after their spawn and their young. This behavior is typical of the freshwater Cichlids, many marine fish such as Damsels and Clownfish, and various other types. Since parental care provides the best guarantee of survival of the young, these fish are not generally as prolific as egg-caterers.

The egg-guardians have developed complicated rituals for pairing off and spawning. Most are territorial, which means that once pair has established itself it drives away all other fish from the selected spawning area, being especially aggressive towards other fish of its own species. These are the species in which the most dazzling courtship displays take place. Often a pair will wrestle or mock-fight and carry out complicated courtship rituals before spawning.

A spawning site is selected — this may be a stone, a leaf, or the tank bottom. Small fish of this type often spawn in a little cave; in the aquarium they will spawn inside an overturned flowerpot. The spawning site is carefully cleaned, and the eggs are fertilized immediately after having been laid. Usually both fish guard the spawning site, driving off intruders and removing any fungus eggs. The parent fish normally fan the eggs with their fins, and may pick up eggs to clean them with their mouths. When the fry hatch, they are gathered into a group by the parents, who guard them until they are large enough to lead an independent life.

In the breeding tank, egg-guardians are for obvious reasons strictly separated from other fish. However, even the parents may still panic and eat their eggs or fry if disturbed, or if conditions aren’t quite right.

Some species have modified their spawning behavior to the point where the eggs are carried in the mouth, completely pro-tested. Usually the female scoops up her eggs as they are laid, then picks at colored spots on the anal fin of the male which closely resemble the eggs. As she does so, the male releases a cloud of milt, fertilizing the eggs within her mouth. With these mouth-breeders, the fry are gathered back into the mother’s mouth when danger threatens.

Another type of protective behavior is seen in the Labyrinth fishes. In fish of this group, the male constructs a bubble nest from mucus. The bubbles are strong, and form a clump on the water surface. The female is enticed to the nest and, after courtship, them ale wraps himself about her and squeezes her so that she sheds her eggs. After fertilization, he catches the eggs in his mouth and spits’ them into the nest. He then guards the nest from all intruders until the eggs hatch.

The ultimate form of care of the young is found among the live-bearers, such as Guppies, Mollies, Swordtails and Halfbeaks. These are the easiest fish to breed, as they tend to ignore the presence of other fish in the community aquarium. They produce relatively few young, but these are well developed and able to swim actively and feed as soon as they are born.

Male live-bearers have their anal fin modified into a special organ, the monopodium, which is used to deposit sperm inside the female. The male courts the much larger female, pursuing her until she is receptive. When the female is ready, the male swims along-side and extends his monopodium sideways, introducing a packet of sperm (a spermatophore) into her vent. Some of these sperms aroused directly to fertilize the eggs, but most are stored to fertilize further quantities of eggs at later dates. The young fish are quite large when born — up to 1 cm (1/tin) in length.

This group of fish is unusual in that sex-changes are not uncommon; a female fish may give birth to young fish and then change to become a normal breeding male. In addition, some types of these fish are thought all to be females, producing young by virgin birth (pathogenesis) without the intervention of males.

Once fish have bred, the task of the aquarist is more difficult. Scrupulous cleanliness is necessary in order to prevent eggs or fry being attacked by parasites or predators. The fry are very viler-able in the early stages. Fish eggs contain yolk, which nourishes the newly hatched fry for a short time, and this yolk is contained in large sac which weighs down the newly hatched fish so that it is unable to swim. For the first few days after hatching, therefore, theory lie helplessly on the tank bottom, or sometimes attached to the sides or stones. They gradually become mobile as the yolk sac is absorbed, and begin to feed. This is the critical time. They must beef on precisely the right type of food, supplied in the proper size; they will then grow rapidly. Nevertheless, there is usually a high mortality rate among such young fish.