Ichthyoplankton

Ichthyoplankton are planktonic, meaning they cannot swim effectively under their own power, but must drift with the ocean currents.

[2][3] Fish can produce high numbers of eggs which are often released into the open water column.

They are usually poorly formed, carry a large yolk sac (for nourishment) and are very different in appearance from juvenile and adult specimens.

The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termed metamorphosis) to become juveniles.

[3] Interest in plankton originated in Britain and Germany in the nineteenth century when researchers discovered there were microorganisms in the sea, and that they could trap them with fine-mesh nets.

This established that fish eggs could be pelagic, living in the open water column like other plankton.

[12] Due to the abundant presence of Na+/K+-ATPase in the basolateral membrane, ionocytes can often be located using immunohistochemistry.

For example, separate studies found northern anchovy (Engraulis mordax) were responsible for 28% of the mortality in their own egg population,[18] while Peruvian anchoveta were responsible for 10%[18] and South African anchovy (Engraulis encrasicolus) 70%.

[19] Fish larvae develop first an ability to swim up and down the water column for short distances.

By the late 1990s, their stocks were collapsing, so in an attempt to save them nine marine protected areas (MPAs) were established off the coast of Hawaii.

Now, through the process of larval drift, fish from the MPAs are establishing themselves in different locations, and the fishery is recovering.

"This is a direct observation, not just a model, that successful marine reserves can sustain fisheries beyond their borders.