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Broodstock in ponds |
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The third type of system involves maintenance of a breeding population in a relatively natural environment such as an outdoor pond, and then transfer of gravid females to controlled conditions for spawning. While the basis for this type of extensive system exists in the literature, this system is little used. It provides preferential grazing of natural productivity, a low-stress, more natural environment, and may be used with or without the alteration of physiological processes which accompanies eyestalk ablation. High quality larvae can be produced through this system. However, it is very limited to use in warm climates, and larval production is subject to natural rhythms, and therefore, inconsistent availability (Bray & Lawrence, 1992). This type of larval production system involves management of a breeding population in a relatively natural environment such as outdoor ponds or raceways. We are aware of only a few commercial operations worldwide which have used this system, but the basis for using it is clear. Adult marine shrimp breed without exception in oceanic or ocean-influenced seawater. A pond environment which roughly simulates their natural environment (e.g., in temperature, in salinity, in light parameters, in natural feed organisms and benthos, with or without natural feed supplementation), stocked at a very low density, will induce penaeids to develop ovaries and spawn, without the requirements of eyestalk ablation (although eyestalk ablation could also be used). Because natural breeding under pond conditions has been observed for a number of species, it is logical to speculate that the inhibitions to ovarian development which are associated with captivity are greatly intensified by the final step into a laboratory environment, where potential breeders are subjected to unnatural noise levels, close confinement, frequent handling, different substrate, unnatural lighting and photoperiod, unavailable live natural animal and plant food organisms, and often markedly different water quality. In outdoor breeding systems, the shrimp population receives many natural cues and diet components, and develops ovaries spontaneously. The primary shortcomings are:
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