Freshwater Fish Egg Incubators (Part I)

J.P. Baldia

Efficient hatchery operations of either freshwater or marine fish species are the first step to a feasible aquaculture operation. Inadequate supply or unavailability of fish seeds for stocking the grow-out facilities will only make the aquaculture business non-viable.

Fish egg development and hatchlings are the most sensitive stages in the life cycle of a fish. It is therefore important that great care must be given to provide them with the best incubation and hatching conditions such as water quality, temperature and water flow to ensure their highest hatching rate and survival.

Cultured fish species have varied types of eggs produced- some release their eggs in water column that either float or sink (Pelagic type eggs) while others produce adhesive type eggs that attach to plants or hard substrate like rocks or gravel (demersal type eggs). Eggs from other fish are deposited in nests with one of the parent fanning the eggs to provide a continuous water flow. Some fish are mouth brooders and the eggs are provided water circulation by the movement of the gill plates of their parents.

In the fish hatchery, artificial incubators simulate these conditions in the wild to provide high hatching rates and survival of the fish larvae. Furthermore, in the natural environment, the eggs are subjected to predation, infections and adverse environmental conditions that result to very low survival of the fish eggs and larvae.

So far, almost all of the cultured marine fish species in the Philippines like milkfish, seabass, snapper, groupers and pompano produce pelagic type eggs, except for rabbit fish (Siganid) which produces a demersal type eggs. For marine fish producing the pelagic type eggs, their eggs are collected from the spawning tank and placed in an ordinary 1-ton capacity Plexiglas or fiberglass tank and provided with moderate aeration to hatch them. No continuous water exchange is necessary because marine fish eggs do not pollute their rearing water when they hatch. On the other hand, the demersal rabbit fish eggs are spawned in a 1-ton capacity tank. The breeders are removed immediately after spawning and the eggs are left in the tanks until they hatch. In either case, no special incubator is needed to hatch the eggs of these marine fish species.

It appears that freshwater fishes are more fastidious when it comes to hatching their eggs. In the freshwater fish hatchery, continuous water flow is necessary because when their eggs start to hatch, the water becomes easily polluted with the egg contents resulting to the immediate death of the fish embryo and larvae.

It is also of utmost importance that fish eggs should not stack together because this will lead to their mortality. The technique generally practiced is to spread them in a single layer at the bottom of the tank or to cause a “tumbling effect” with the use of a regulated water pressure and aeration.

(To be continued)