Broodstock - Management

Management

Broodstock management involves manipulating environmental factors surrounding the broodstock to ensure maximum survival, enhance gonadal development and increase fecundity. Such conditioning is necessary to ensure the sustainability of aquaculture production. It is also utilised to increase the number and quality of eggs produced and control the timing of maturation and spawning.

Choosing species to use requires consideration of the biology of the species. This includes their size at maturity, method of reproduction, feeding behaviour and ability to tolerate adverse conditions Farms also consider whether they grow their own broodstock or obtain them from natural populations. Where natural populations are excluded, the farm can be considered a self-sustaining unit independent of external genetic influence.

Pond-reared broodstocks are selected, often as immature juveniles, and grown out in suitable conditions to sexual maturity. These animals require stable water characteristics and a well-balanced, species-dependent, protein rich diet. This enhances the germinal tissue for future seed stock as it is formed in juveniles.

The pond or tank in which broodfish are held must be a suitable size to hold and condition the broodstock. Dependent on the species involved you need to alter the number of individuals, and often separate the sexes. Sex separation enables the broodstock males and females to be subjected to different conditions where necessary. For example, male and female sturgeons respond to different hormone levels, this also allows more control over eggs and sperm.

The characteristics of the water in which the mature broodstocks are held must be manipulated. The aquaculturist must consider the appropriate oxygen concentration, temperature, and pH of the water all of which can be species specific.

The feeding regime of broodstocks is species specific and requires consideration of timing and composition of the food. Protein, lipid and fatty acid composition is particularly important. The quantity of food intake can be altered to influence spawning and maturity, for example low rations have been shown to reduce the number of fish reaching maturity while increasing the fecundity of those which do.

When fry are desired, spawning can be induced in broodstocks by manipulation of relevant environmental factors. In particular the photoperiod can be altered to imply that it is time to spawn. A shortended photoperiod is known to advance spawning times while a lengthened photoperiod can delay spawning. Artificial light can be used to change the apparent day length and indicate different seasonal features so as to delay spawning. Water temperature can be increased for the same purpose. Following spawning the female broodfish are often stressed and have lost weight. They require extra care and abundant feeding at this time to ensure survival to the next spawning season.