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Spawning Induction

Technical factsheet on the different methods for inducing spawning in fish

© Marie,D.Inra
Spawning in fish is regulated by environmental cues, interpreted by the brain-pituitary-gonad axis. These cues include variables such as water temperature, photoperiod, habitat, behavioural stimulation and changes in salinity, pressure and food supply. Different fish species respond to different cues, or a combination of cues. The brain detects the relevant environmental changes and produces gonadotropin-releasing hormone (GnRH), which induces the pituitary to release gonadotropins, sending messages to the gonads for egg development and spawning.

How can spawning be artificially controlled?
Administration of hormones - gonadotropins (human chorionic gonadotropin, hCG; pituitary extracts, purified fish gonadotropins) and gonadotropin releasing agonists (GnRHa or LHRHa)
Different temperature regimes (decrease / increase)
Different light regimes
Habitat modifications (addition of vegetation etc.)
Behavioural stimulation (presence of other fish etc.)
Why is this useful to the fish farming industry?
This technology allows the industry to guarantee and plan production and produce a known quantity and quality of eggs. Spawning may be synchronised and planned at a particular, convenient time of year (in relation to markets, climate, demand etc.). Efficient control of spawning also reduces dependency on wild broodstock.
How is spawning control useful for conservation?
The ability to control spawning in captivity allows for the management of captive broodstocks, reducing dependence on collection of wild fish from their spawning grounds. Some fish farming activities are currently completely dependent on collection of wild stock, such as the bluefin tuna and freshwater eel industries, which is putting immense pressure on wild populations, threatening the survival of the species. Research on the bluefin tuna currently focuses on the induction of spermiation, ovulation and spawning; whereas for the freshwater eel focus is on the induction of gametogenesis and artificial spawning induction.
What are the future requirements for research?
Improved understanding of the environmental cues for egg development and spawning and their influence on the neuroendocrine system.
Development of pharmacological methods for the complete control of reproduction processes, such as spermatogenesis, oogenesis, final oocyte maturation, spermiation and spawning.
Developement of biochemical assays for monitoring reproductive function, based on the assessment of reproductive hormones (e.g. gonadotropins, sex-steroid hormones) and vitellogenin in the plasma, muscle and mucus.
This factsheet was prepared with the expert assistance of scientist Constantinos Mylonas.

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