Flatfish

Flatfish: Pleuronectiformes

Looks

Flatfish are round, sandy-coloured fish with both eyes on one side of the head. Babies are born with an eye on either side of their head. The second eye migrates to the other side while the fish is still developing—that way they can get a good view of the water above without one side of the face being mushed into the sand. Some flatfish have both eyes on the right side, some on the left. On the side with the eye, most species have darker skin, and on the eyeless side, their skin is pale. They use camouflage to escape from enemies: and indeed, it seems to work very well!  They blend in with the sandy bottom of the sea or rock pools. (See Habitat)

Feeding

Flatfish eat mostly crustaceans, polychaetes, small fish, and fish spawn. 

Habitat

Most flatfish live in seawater. It is not decided officially whether they can live in fresh water, though there have been sightings all over the place of flatfish in freshwater pools.

Breeding

Female flatfishes lay eggs, sometimes more than a million, that she releases into the water for the male to fertilize. The eggs hatch after a few days into long, spiny plankton-like larvae, with eyes on both sides of the head. As they develop the eye moves across the head to the other side (see Looks) and their body grows rounder. The larvae have spines to protect them in the early stages, and a gas-filled swim bladder to help them stay stabilized in the water, both of which they lose as they grow into adults. They sink to the bottom and lie with the eyeless side on the sand.

When just hatched, the larvae are less than 1.3 centimeters (that’s ¹/₂ inch) long!

See here for information on a swim bladder:

Link to Wikipedia

Lifespan

Varies according to species.

Dover Sole: 58 years male, 53 years female

Starry flounder: 24 years

English Sole: 22 years

Sand Sole: 10 years

Three-spined Stickleback

Link

Looks

Sticklebacks are small fish only a few inches long, with spiky fins running down their back. Interestingly, Sticklebacks have no scales. Some species, however, have armour plates to protect them. Three-spined Stickleback females are light blue-green with a pale pinkish underbelly, and the males of this species are the same, but with a silver belly instead of pink.

Habitat

These little fish live mostly in the ocean. Some also make their homes in freshwater lakes. Long ago, after the ice age, glaciers and ice melted, allowing the Sticklebacks to make homes in the freshwater lakes and streams. In there, the predators were faster but not as strong, so the freshwater Sticklebacks evolved to suit their new territory’s needs. The freshwater species have no spines or armour plating, and are faster and more agile than their cousins in the sea.

The ocean Sticklebacks live only in the Northern Hemisphere, prefering coastal, slow-flowing water with marshes and bays.

Feeding

Sticklebacks’ diets consist of small crustaceans and the lavae of fish.

Breeding

(Three-spined Stickleback—other species have a similar way of breeding)

First, the male fish creates a bird-like nest out of vegetation. Then he attracts a female and invites her inside. The female Stickleback will lay a clutch of about 100-150 eggs. Afterwards, the male guards the nest, driving away other males and protecting the eggs until they hatch.

Lifespan

(Three-spined)

These small fish live for about 3 years.