An understanding of the fundamental processes determining fish reproduction is essential in order to understand species-specific reproduction strategies and triggers; to control sex ratios, puberty and spawning; and hence enable more efficient and sustainable production of a diverse range of species. A better understanding of fish reproduction also decreases the reliance on wild fish populat...

The primary species are goldfish, carp and rainbow trout. However, research has also been carried out on salmon, catfish, sea bass, sea bream, eel and tilapia. Other species such as cod, flatfish, mullet, perch, pike or barramundi are also now well studied. Small fish such as zebra fish, medaka and mosquito fish are increasingly used as laboratory models.

Fish exhibit both seasonal (daylength influenced) and daily (light/dark cycle influenced) endogenous rhythms. If they are maintained in constant environmental conditions of temperature and photoperiod, they will still reproduce at one year intervals, indicating that they have an endogenous annual clock that tells them when to reproduce. However, this clock can be largely influenced by change...

In aquaculture, this is a group of sexually mature male and female individuals, kept separate for breeding purposes. The advantage of maintaining a broodstock is that eggs and fry can be produced in a controlled environment, with no reliance on wild populations.

Puberty is the development period covering the transition from an immature juvenile to a mature adult reproductive system. The initiation of puberty in males is marked by the onset of sperm production and in females by the onset of egg production. Under farm conditions some species (e.g. cod, sea bass, salmon) enter puberty precociously, leading to decreased flesh quality and growth performa...

In numerous species of fish, sex is determined principally genetically. For most fish species, the differentiation of the gonad into a testis or an ovary can be strongly influenced by hormonal, environmental or social factors, whose modes of action are on the whole poorly understood.

Many, if not all, commercially important species display significant differences in size between the sexes. In some species, one sex enters maturity earlier than the other (e.g. salmonids), in some cases reproduction may start very early in life and occur all year round in captivity (e.g. tilapia). Reproductive status greatly affects individual growth rates as less energy is committed to som...

Fish sex may be manipulated by the direct application of hormones. However, direct hormonal methods are not permitted in many countries, indeed within the European Union only the use of certain androgens (methyltestosterone) is permitted in fish farming and then only under certain derogations. This method is currently used on rainbow trout in order to obtain large female individuals for the...