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Aquaculture at the MIT Sea Grant Finfish Hatchery
Gloucester Maritime Heritage Center

Note: words in red link to an online glossary (or dictionary) of related terms.

Fish Life Cycle

The development of marine finfish eggs is temperature dependent among all teleost (bony fish). Once the egg is fertilized, the embryo will form inside the hardened egg. The embryo will start to develop organs, and eventually eyespots and the tail can be seen inside the egg. The embryo will develop pigmentation spots along the body. The tail will wrap around the egg to the head. If the species lives in warmer waters, the embryo will hatch more quickly. Colder water species hatch slowly, and the eyes and pigmentation will be fully developed at hatching. The tail of the embryo will break out of the shell and the embryo becomes a free-swimming larva.

Once the fish is hatched, it is known as a larva. Newly hatched larvae have a yolk sac that is a source of nutrition for the larvae. They absorb their yolk sac for several days until they are developed enough to feed on live prey.

Yolk sac larvae can survive for 2-4 days by feeding off their yolk sac food supply. This is called endogenous feeding. The length of the yolk sac period for larvae is dependent on the culture temperature and the species of fish. The warmer the water, the faster the fish will use up their yolk reserves. Once the larvae mouth has formed and the eyes are partially developed, the larvae can be offered a live feed.

Feeding on organisms or particles in the water column is called exogenous feeding. Live feed is essential to the early stages of developing larvae. Because their eyes are underdeveloped at hatch, the larvae need to be offered a feed that is moving around to help stimulate a feeding response.

When the larvae hatch, they have a finfold around their whole body that looks like an outline when observed under a microscope. This fold will eventually develop into fins, beginning with the process of metamorphosis.

Metamorphosis is the process that signifies the end of the larval stage. After metamorphosis, the fish are considered juveniles and will acquire characteristics of an adult fish: body features, coloration, fins, etc. Metamorphosis also denotes full organ development; it occurs at different times for different types of fish. For example, some fish will metamorphose in 20 days, whereas some will not go through the process until 4 months of age. Metamorphosis is a very stressful time for the fish, which means there is a point of high mortality, known as a bottleneck. The larvae are given a different type of feed during this period because they are now juvenile fish. Weaning fish to a new diet is also a stressful part of the culture process.

Juveniles are usually resistant to stress (temperature, water quality, etc.) over time. As long as the culture environment remains healthy, the fish should thrive on dry feed and show significant growth rates. Juveniles are not considered adults until they become sexually mature. The developmental cycle is complete once spawning to egg and larvae to juvenile and adult has been accomplished.

Adults are characterized by their ability to reproduce.

Related Links:

All About Aquaculture
Species raised at the Finfish Hatchery
Table Top Recirculating System
Facilities overview The MIT FinFish Hatchery
MIT Sea Grant's Aquaculture Curriculum On-line