The 5 Stages of Fish Metamorphosis

Like other organisms, fishes undergo metamorphosis too. Metamorphosis, the term commonly used for animals (synonymous with ‘evolution’ for humans) is a biological process by which an animal physically develops after birth or hatching. It involves relatively abrupt change in animal’s body structure through cell growth and differentiation. While most fishes undergo complete metamorphosis (“holometaboly”), there are some that undergo incomplete metamorphosis (“hemimetaboly”), and in very rare cases, no metamorphosis at all (“ametaboly”).

Tilapia (O. niloticus), Bangus (C. chanos), Pompano (Tranchinotus), and Seabass (C. striata) are examples of fish species that undergo complete metamorphosis. This type of metamorphosis consists of 5 stages namely: a) egg, b) larva, c) fry, d) juvenile fish, e) adult fish. It’s not that hard to picture the 5 stages of fish metamorphosis as it is closely alike to the humans’ stages of life. During mating the egg becomes fertilized and whether brood or released on the nests. If the temperature is low and cold, it could take up to a week and more. In the contrary, if the water is hot or (for tank/aquarium owners) you heat it once the eggs are fertilized, they may hatch in less than three days. Generally, it would take from a couple of days to a week before eggs starts to hatch and tada! The first stage was completed.

The egg hatches in 5-8 days. Its eyes and body lack pigment but the yolk sac is covered with fine black spots. The larval stage begins when the tiny sturgeon has absorbed the yolk sac, about 9-18 days after hatching. As soon as the spawn assume the shape of the fish and grow to about 1–2 cm it is known as fry. Fry – refers to a recently hatched fish that has reached the stage where its yolk-sac has almost disappeared and its swim bladder is operational to the point where the fish can actively feed for itself. Juvenile: The time fish spend developing from fry into mature adults varies among species. When the transformation or metamorphosis from larva to juvenile is complete, that is, when the larva develops the features of a juvenile fish. These features are that all the fin rays are present and that scale growth is under way. The stage completes when the juvenile becomes adult, that is, when it becomes sexually mature or starts interacting with other adults. 

Most fish do not survive to become adults.

Incomplete metamorphosis occurs where there are fewer than four stages, which is the case for many fish. Shortly after they hatch, many fish essentially have all the features of an adult. A typical fish life cycle starts with an egg; once the fish matures and can reproduce and lay eggs, it becomes an adult. For example, Catfish (Siluriformes), once they hatch, the male protects the young for several days until they swim off to feed. 4The yolk sac larvae have large yolks and are about 6-10 mm in length. Their bodies are transparent with some pigmentation on the tops of their heads. Their barbels or whiskers are very long compared to their head. Their tails change from a club-shape to more obvious double lobes which are quite rounded. The yolk sac larvae stay on the bottom for 2-5 days, and then swim to the surface to feed. Catfish do not exhibit a post-yolk sac larval stage. Juvenile catfish are 15-42 mm in length. They look very much like an adult with their sharply pointed forked tail. Catfish mature and become adults when they are 5-8 years old. They are dusty-grey to dark grey-blue in colour, often with scattered spots. Adults can weigh over 14 kilograms!