Aquaculture Research

Farmed Fish Maturity Control (Artificial Extraction of Eggs and Sperm)

Nissui has developed maturity control technology for artificially extracting gametes from brood stock of target species and conducts research into rearing fish to produce better farmed fish strain.

Nissui is attempting to develop integrated aquaculture, overseeing the entire process from fertilized eggs to product shipment.
To lessen dependence on natural resources for aquaculture, we are working on developing maturity control technologies for artificially extracting gametes (eggs and sperm) from target species brood stock.

Artificially extracting eggs from a yellowtail
(to reduce stress, the eggs are extracted
after the fish is anesthetized)

We Succeeded in Artificially Producing sfingerlings of Aquaculture Target Species

Many aquacultures today depend on obtaining fingerlings from natural resources. But today, when fish catch resources are in danger of being depleted, producing seedlings artificially lessens impact on the environment and helps stabilize production.
But first, brood stock needs to be reared, brought to sexual maturity and functional gametes (eggs and sperm) extracted.

To date, Nissui has succeeded in artificially producing fingerlings of various farmed fish species--salmon, trout, yellowtail, red sea bream, eel, tiger puffer, bluefin tuna and others--and has commercialized the seedlings of some species.

It is in fact quite difficult to induce brood stock sexual maturity in a planned and consistent fashion, and we are continuing research in this area.

Brood stock are reared in large tanks whose water temperature, daylight length and other conditions can be controlled.

Research to Determine Conditions for Rearing Brood Stock to Lead to Sexual Maturity

Many farmed fish species reproduce in specific seasons and have a clearly defined reproductive cycle.
But in an aquaculture setting, some species fail to spawn or produce viable eggs and sperm.

The reproductive cycle is affected by external environmental factors like water temperature, tides and day length.
Farmed fish receive stimuli from those factors through their sensory organs. The brain collates this information, which then influences development of the reproductive glands.

Reproductive hormones and other factors are involved in the reaction process.

Examining yellowtail ovarian tissue
(ovarian tissue is extracted from live yellowtail to check progress of development)

But there is much that is still unknown about reproduction, and since different species reproduce in very different ways, we need to conduct research on individual species.

To develop technology to control maturity, Nissui is continuing research on target species to discover the physiology of reproduction at the molecular level, to help identify the condition of brood stock, the kind of environment they are reared in, and what kind of reaction occurs that triggers sexual maturity.

Controlling the Environment to Create Fish in Season Year-round

Thanks to research conducted so far, in certain species, actively controlling the brood stock raising environment can trigger sexual maturity outside the usual spawning period. This has allowed us to successfully fertilize eggs through artificial insemination.

For example, wild yellowtail spawn in the southern part of the East China Sea around February. By controlling the photoperiod and water temperature, we have successfully spawning and artificially inseminated eggs in November and December. (*1)

Image of yellowtail ovarian tissue

Immature eggs inside the ovary (egg mother cells)

Egg mother cells developed as a result of environmental manipulation

Rearing yellowtail in cages outside the normal period using eggs and fingerlings we have created allows us to deliver a steady supply of just-right size tasty yellowtail during spring and summer, when supplies of this species are usually scarce.

  1. *1Part of this research was conducted with the Fisheries Research Agency, an independent administrative agency of the government.

A Kurose yellowtail cage

Selecting Specific Brood Stock with Desirable Traits to Create Superior Farmed Strains

The ability to control sexual maturity offers other advantages in addition to the ability to produce eggs and fingerlings at desired times.

Advantages of Controlling Sexual Maturity

  • Enables production of eggs and fingerlings at desired times
  • Creating the next generation from brood stock with desirable traits enables us to produce and rear species with superior qualities

Unlike livestock (cattle, swine or poultry) rearing, in most cases farmed fish is genetically identical to wild fish.

But if sexual maturity can be triggered and artificial insemination used, the next generation can be produced from brood stock with desirable traits, enabling us to produce and raise species with superior qualities.
Nissui conducts research and development to identify and select individuals with desirable traits for farmed fish, control fish bloodlines through DNA analysis and develop efficient methods for rearing fish using genetic analysis.