Fish Breeding 

Many aquarists soon develop a yearning for the patter of tiny fins, perhaps because a species breeds unprompted in its community tank, perhaps because of an interest in conservation. Indeed anyone maintaining a rare or endangered species should feel duty bound to try to breed it in order to reduce depletion of wild stocks. Legislation is currently being discussed which may forbid the importation of many (perhaps all) fishes from the wild, so the continued presence of many species in our aquaria may depend on captive breeding. You too may have an important role to play, rather than just breeding fishes for interest and amusement.

Unfortunately far too much breeding is unplanned and/or ill-considered, resulting in inferior stock. Many species which have been captive-bred for generations are now mere shadows of their splendid wild ancestors. They are also often unhealthy as lack of selection has reduced inherited vigour. A comparison of today’s stock with photographs taken of the same species 20 or 30 years ago can be horrifying.

Breeding top quality fish depends on three factors: selection of parent stock; avoiding indis criminate inbreeding; and rigorous culling of inferior offspring. Fishes intended for breeding should be vigorous, of good size and colour, with no inherited flaws in form and finnage never the little chap you felt sorry for because he was the smallest, or the one with the funny twisted tail. Ideally, they should be unrelated, although line breeding (the planned mating of related individuals with a particular objective, usually the breeding of “fancy” strains of fish, for example, guppies) is acceptable. Rear only the best of the brood, even if there is a ready market always cull deformed and undersized specimens (runts). The normal practice is to feed rejects to other fishes but if you are too soft-hearted, an aquarist friend will probably have a hungry predator.

Most fishes do not actively care for their eggs, relying on sheer numbers to ensure the survival of a few , but in the restricted space of an aquarium, all tend to become caviar for tankmates. Some species produce live young , which likewise usually become snacks. Some fishes, however, notably cichlids, actively care for both eggs and fry, their attendant territoriality often being to the detriment of anything sharing their aquarium. The courtship of some types can be equally traumatic for tankmates. For these reasons any serious attempt at breeding will usually require intervention by the aquarist, and frequently separate quarters for the breeding individuals.

The Breeding Tank

Natural requirements for water chemistry and habitat may have been compromised in the community tank, but the breeding tank should provide optimal conditions for its occupants, because without the correct water chemistry eggs often fail to hatch.

Some species are seasonal breeders, requiring one or more triggers to stimulate spawning in effect a simulation of what happens in Nature: the rains come (frequent water changes), food supply and quality improve (lots of live food), and then it gets hotter (raise the temperature). Species from cool and temperate zones may also be triggered by longer day length (increased light intensity and duration).

Some fishes require a particular spawning substrate (the surface on which, or material in which, eggs are laid). These special conditions are best created in a separate breeding tank, which must, however, in other respects conform to normal criteria for setting up and maturing aquaria for the species concerned.

The key to successful breeding is PATIENCE. Do not expect your fish to breed the moment they are installed in their desirable residence a change of environment is often the fishy equivalent of a cold shower! If nothing happens after a few weeks resist the temptation to fiddle with the environment (triggers apart); the fish will probably have only just settled down enough to consider breeding, and your interference will set them back to square one.

Rearing

Mating and post-mating procedure varies for different types of fishes but there are general principles for fry rearing, whatever the species. First, fry are more delicate than their parents. They tend to be more susceptible to poisoning by nitrogen cycle by-products, so particular attention must be paid to water quality. Filtration turnover must, however, be gentle, as otherwise fry may be sucked in; small air-operated sponge filters are ideal. Zeolite, a material that absorbs ammonia, can be useful a small amount scattered on the bottom of the tank, or suspended in a nylon bag (made from a stocking), will compensate for any hiccup in the filtration. Small fluctuations in temperature and water chemistry can have dire effects, so water changes, which should be small and frequent, require extra care.

Avoid moving tiny fry if possible this often causes losses and/or a check in growth. Never use a siphon to move fry; this will cause physical damage. Instead, use a meat baster or small soup ladle (extremely useful items when rearing fry) to transfer tiny fry; and for larger ones a small fine-meshed net designed for the purpose and available from your local dealer.

Types of Breeding Tanks

Some fishes, for example small barbs, commonly eat their eggs. Reduce the level of water in the tank and place a layer or two of marbles along the tank bottom. The reduced water level means a shorter time that the eggs are in danger while they fall to the bottom of the tank, and the marbles act as a highly efficient fish-proof egg trap. Once spawning is over, remove all the eggs.

Another way of saving eggs is to drape a piece of finely meshed netting in the water. The fishes are placed above the netting, and when they spawn the eggs fall through it to safety. This method is suitable for small fishes such as danios.

A dense section of plants is required for breeding tetras. The fishes make spawning runs through the plants; their eggs are adhesive and remain trapped in the plants, safely hidden from other predators to hatch.

Rainbowfishes can be successfully bred by the use of artificial mops. These are placed just inside the tank and provide a safe environment for the female fish to lay her eggs. It is then a simple job to collect up the eggs and hatch them in separate shallow dishes. Spawning mops are also used for breeding some killifishes (egg-laying cyprinodonts).

A useful device for breeding livebearers is a breeding trap which can be placed in the main aquarium. The holes in the netted trap allow the fry to swim to safety. It is advisable to allow the female to rest for a few days after giving birth before being released into the main aquarium.

Feeding Fry

Fish eggs, if viable, hatch after one or more days, but the larvae obtain nourishment from their yolk-sacs for several more days thereafter. They cannot swim at this stage and normally lie on the bottom or remain attached to the spawning substrate. When all the yolk has been absorbed they become free-swimming fry and start to look for food. Although they will find some natural foods (microorganisms, algae) if the tank has been set up for some time, they usually need supplementary feeding immediately. The type of food offered initially depends on the size of the fry; the tiniest will need infusorians: microscopic aquatic organisms that can be cultured by putting a lettuce leaf in a jam-jar, adding boiling water, and leaving the jar on a sunny window ledge. When the water goes cloudy it is ready for use, and a portion can be drawn off with the meat baster and squirted into the shoal of fry. If the culture fails, there is a commercial substitute called “Liquifry” available. The next size up of food, suitable for many newly free swimming fry, is the freshly hatched nauplii of the brine shrimp (Artemia salina), whose eggs (available from retailers) are hatched in salt water in lemonade bottles or large sweet jars. Loricaria species (whiptail catfish) with eggs.

The salt concentration depends on the geographical origin of the shrimp, so buy a brand with instructions. Start a culture two to three days before the fry are due to become free swimming; once active, this will last for two to three days, so three, started at two-day intervals (and replenished on their sixth day), should suffice. Brine shrimp should always be rinsed in fresh water before feeding, to remove excess salt.

Breeding coral fishes presents almost insuperable problems, though some success has been achieved with damsel and clown fishes. Feeding the fry remains a major hurdle to overcome.

Another excellent fry food is microworm, cultured in plastic tubs of cold porage (or similar); the worms proliferate rapidly and crawl up the sides of the container away from the culture medium, and are harvested on a fingertip which is then rinsed in the tank. Starter cultures, with instructions, are often advertised in the aquatic press; thereafter a spoonful of established culture can be used to start others after about 10 days the aroma tends to become unpleasant.

As fry increase in size, they can take increasingly larger items, tiny pond foods such as Cyclops, Bosmina, and small Daphnia; cod roe; crumbled flake; and small particles of other foods.

You will need to raise the young fish to at least 2.5 cm (1 inch) long before they can be sold; good water quality and ample space are just as essential to growth as diet, so raise only as many as you can sensibly cope with, and regularly cull substandard individuals. The wise breeder canvasses potential customers (friends, dealers) early on (perhaps even before breeding a species at all) to find out how many fry it is worth raising; even if you could sell the entire brood, remember it is preferable to raise a small number of top quality fry rather than a large number of poor ones.

Fish Breeding FAQs

Sandra

A London-based Veterinary surgeon, Sanja is also an avid writer and pet advocate.