ANALYSIS - Controlling the reproduction of farmed fish has come a long way in the past 40 years and it is essential for the growth of a sustainable industry, stated Yonathan Zohar, University of Maryland, US, at the Elsiever Aquaculture 2013 conference in Gran Canaria, Spain. Lucy Towers, TheFishSite Editor reports.
Enhancing fertility through the induction of spawning is required for broodstock management and the predictable production of eggs and fry.
In the early days, hGC was injected but fish were dying, so it was clear that a new approach was needed, stated Dr Zohar.
In finding a new method, it was important to understand how hormonal failure was linked to the lack of ovulation and spawning.
Tests revealed that the lack of ovulation and spawning was due to the failure of the primary gonadotropin (LH) release from the pituitary gland. In response to this, scientists studied brain gonadotropin-releasing hormones (GnRHs) and designed GnRH analogs which could be injected into the fish. However, the effects of this did not last long enough for successful ovulation.
This therefore highlighted a need for a much more prolonged prescence of GnRH analogs in the fish's circulation.
In response, scientists have now created a tailored polymer based delivery system for different fish, ie daily spawners, monthly spawners
It is not just reproduction that is important, the sterility of farmed fish is also required in many fish farming operations.
Sterility helps to achieve better growth and prevents the genetic problems which escaped farmed salmon may have on wild salmon populations, especially genetically engineered salmon, which are much bigger in size then normal salmon.
Previous work found that tripolids are not 100 per cent affective and therefor a new approach to sterility was needed.
In order to carry out this work, scientists used zebra fish as a model.
Scientists studied the early development of the GnRH system and discovered that the ablation of the GnRH3 system or distrupting the early migration of the primordial germ cells (PGC) produced sterile fish.
In conclusion, Dr Zohar stated that the GnRH system and gonads establish very early in the development of zebrafish and other farmed fish and that by distrupting the early establishment of the GnRH system or the early migration of PGC’s, it is possible to induce sterility.
Although this procedure is not used in aquaculture at present, studies are soon to commence on its use in farmed salmon, said Dr Zohar.
The field of reproductive physiology in fish has made huge strides in recent years and sterile farmed fish will be important in the future.