1. Introduction
Inter-specific hybrids have attracted attention because they can improve productivity through hybrid vigour, combine desirable characteristics found in one species with those
Ž of another, or produce animals that are sterile Chevassus, 1983; Hedgecock, 1987;
. Longwell, 1987; Menzel, 1987 . The development of artificial insemination techniques
and in-vitro fertilization for crustaceans has assisted the production of inter-species Ž
. crosses in this group Clark et al., 1973; Berg et al., 1986 . Several interspecies hybrids
of penaeid prawn species have been achieved — Penaeus setiferus = P. stylirostrus Ž
. Ž
. Lawrence et al., 1984 , P. setiferus = P. schmitti Bray et al., 1990 , reciprocal crosses
Ž .
of P. monodon and P. penicillatus Lin et al., 1988 , and P. monodon = P. esculentus Ž
. Benzie et al., 1995 .
The number and hatch rate of hybrid eggs, and the survival of hybrids to post-larval stages have been low compared with the results of intra-specific matings, and most
Ž reports focus on these issues rather than the characteristics of the hybrids Benzie et al.,
. 1995 . Growth rates relative to the parent species have not been assessed in most
Ž .
studies, but Lin et al. 1988 recorded that the reciprocal P. monodon = P. penicillatus hybrids grew faster than both of the parental species and suggested that hybrid vigour
Ž .
had been demonstrated. Benzie et al. 1995 successfully produced P. monodon = P. esculentus hybrids in an attempt to create a line having the fast growth rate of P.
monodon and the attractive banding patterns that enhance the market value of P. esculentus. However, these authors noted that the lack of controls in their experiment
prevented a critical assessment of the growth rates of the hybrid.
Prawn growth rates are highly variable depending on the precise environmental conditions in which they are reared. No published study of prawn hybrids to date has
Ž included the appropriate controls i.e. the culture of pure larvae from each of the
. parental species together with the hybrids to determine the growth rate of the hybrids
relative to the parental species. The aim of the present paper is to report the results of experiments where hybrids
were reared together with larvae produced from pure parental species matings to provide a critical assessment of the growth and survival of P. monodon = P. esculentus hybrids
relative to their parental species.
2. Materials and methods
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