Biology of Finfish and Shellfish

4.7.1.2. Larval development

The larval phase begins once the embryo is free from the egg membrane. The embryo now ceases to be curled up, becomes increasingly fish like, and continues to rely on its yolk or mother for nutrition (Moyle and Cech, 1988). The duration of this phase, however, varies widely among species. As soon as the yolk content is absorbed (generally yolk sac is absorbed on the third day in case of Indian major carps) the larva should develop the ability to capture food organisms. The larva is now carnivorous taking mainly zooplankton regardless of the species which is herbivorous or carnivorous in later (adult) stage. A larval fish, while still using its stored yolk, is called either a prelarva or a yolk sac fry. After absorption of the yolk, it is called post larva (advanced fry). Larval development continues until the fry reaches the fingerling stage, when it more or less resembles the adult. Usually mention may be made that the development in fish larvae does not occur at the same rate among all the individuals in a population. Biswas and Phukon (1989, 1990, and 1991) in a series of experiment observed that hatchlings emerging from the eggs of same brooder and same time are not equal in size. This variation in size becomes more conspicuous when the hatchlings are about two weeks old. It is probable that the sudden increment of growth in a section of fish spawn is related to genetical factors.