Stocking density and sex ratios

For short-term holding, BC males and females can be held either individually or more often in communal tanks at a ratio of one BC male to ten females. Males usually develop a harem and defend it and their territory from other males. Once mating has occurred, the females are moved to darkened conditions and fed a mixed diet (see section 4.2.5). It is imperative that minimal disturbance of females occurs. Once the eggs have become grey and are thus due to hatch within a few days, the females may be transferred to a hatchery system. Many types of spawning systems are employed and these are described in more detail in this chapter (see section 4.3.1).

For long-term holding, the density of brooders in the holding tanks appears to influence the egg carrying capacity of females. The total number of eggs which eventually hatch is reduced at higher densities. A stocking density of 1 individual per 20 to 60 L and a ratio of 1 or 2 BC males per 20 females are recommended. If broodstock are collected in early to late October (April in the southern hemisphere) and larval production is planned for December or January (June or July in the southern hemisphere), then OC males should be stocked at a ratio of 2 or 3 OC males per 20 females in addition to the BC males. The OC males should weigh more than 35 g when stocked. If newly hatched larvae are needed after March (September in the southern hemisphere), then OC males should be stocked at 3 to 4 per 20 females to offset increased mortality of males over a longer holding period (Daniels et al. 1992). Varghese et al. (1992) recommended a sex ratio of either 1:3.75, 1:4 or 1:4.75 (male:female) for maximum oviposition in M. rosenbergii. Malecha (1983) suggested 1:4 or 1:5 and Sureshkumar & Kurup (1998) suggested a ratio of 1 BC to 4 females for optimal oviposition and hatching; however, ratios of 1:2 and 1:5 also produced good results.

Sandifer & Smith (1978) described a closed recirculating system in South Carolina for maintaining broodstock, hatching larvae and nursing juveniles. In the broodstock system, they stocked prawns about 30 g in 2000 to 5000 L tanks at densities of 30 to 90/m2 of tank floor with a male to female ratio of 1:4. Within each tank they placed an artificial habitat. These workers achieved an overall average of 62% survival over 5 months. Approximately 25% of the females were found to be ovigerous every 2 weeks.

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