1 NOVEMBER 1998
BROODSTOCK MANAGEMENT AND THE OPTIMISATION OF SEED SUPPLIES
N. Bromage
The ability to fully control sexual maturation and spawning is a primary requirement for successful aquacultural production. The artificial induction of spawning either by hormonal or environmental manipulation enables supplies of eggs and fry, sometimes generically referred to as seed, to be made available even from those fish which do not naturally spawn in captivity. For species of fish which are able to mature and spawn under farm conditions, controlled reproduction can provide seed at precisely those times required by ongrowing farms and not just during the few months of the year when natural spawning occurs. In turn the availability of seed on demand enables grow-out farms to spread their production of market-sized fish throughout the year.
Effective seed production also demands a thorough understanding of the special husbandry and nutritional requirements of broodstock fish because diet and management procedures can have significant effects on fecundity (numbers of eggs produced), egg size and egg and larval quality or survival.
In addition to being able to produce good quality seed on demand it is also essential that farmers are able to control the gender or sex of the seed which is produced. This ensures that the metabolic activities of the fish produced from this seed and more importantly the inputs of high cost artificial feeds are wherever possible channelled into the growth of saleable flesh and away from gonadal growth and sexual maturation.
The ability to both control the timing of spawning and to determine the sex of the progeny assumes a greater importance with the intensification of fish farming. Generally, intensification demands greater tonnages of production in order to reduce unit costs through economies of scale. This greater volume of product has to be retailed through the chain multiple or supermarket stores with less reliance on local or farm gate sales. Such markets require a continuity of supply of fish of consistent size and quality throughout the year. Continuity of supply is only possible when the control of reproduction of the fish under cultivation allows input of seed to be made at any time of the year. Avoidance of the problems of maturation also enables farmers to meet the strict product specification relating to fish size and flesh quality invariably imposed by retail organisations.
Given the importance of effective broodstock management in the provision of all-year-round supplies of seed in modern aquaculture, the present review will consider the basic mechanisms of controlling reproduction, gender and smoltification and describe how these may be modified by photoperiod and melatonin and other hormonal and dietary influences to optimise supplies of seed.
(Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, Scotland, UK)