Matthew Kenway

Genetic mapping of the black tiger shrimp Penaeus monodon with amplified fragment length polymorphism

Abstract We report construction of an initial genetic linkage map for the black tiger shrimp, Penaeus monodon. Mapping was carried out using polymorphic markers derived from 23 Amplified Fragment Length Polymorphism (AFLP) primer pairs. These were analysed on three reference families of known pedigree. A total of 673 polymorphic AFLP loci that conformed to expected Mendelian segregation ratios were scored in three families, and these were used to construct separate male and female linkage maps for each family. AFLP markers that consisted of a segregating fragment of the same size, amplified with the same primer pair in two or more of the reference families, were considered to be common markers. 116 such common AFLP markers were used to construct a common linkage map across the three families. This linkage map has 20 linkage groups covering a total genetic distance of 1412 cM. Future directions for genetic mapping in P. monodon are discussed in light of these initial data.

Estimates for the heritability of size in juvenile Penaeus monodon prawns from half-sib matings

Abstract Eighteen half-sib groups of the giant tiger prawn, Penaeus monodon , were obtained using artificial insemination of two females by each male. The total length (mm) and wet weight (mg) of the young were measured at 6 and 10 weeks after hatching. Sire component estimates were approximately 0.10 for both total length and wet weight at each age. Dam components were greater suggesting large non-additive genetic effects and/or common environment effects that could not be differentiated on the available data. A reduction in the dam component for both total length and wet weight from approximately 0.5–0.6 at 6 weeks to 0.3–0.4 at 10 weeks suggested significant maternal effects were present. The results emphasised the strong environmental controls on prawn growth, particularly potential maternal effects that are likely to play a role earlier in development. These influences resulted in highly variable data, emphasising the need for higher degrees of replication of sire and dam groups in order to detect significant sire effects in P. monodon .

Interspecific hybridization of the tiger prawns Penaeus monodon and Penaeus esculentus

Interspecies hybrids were produced by artificial insemination of Penaeus monodon females with P. esculentus males. Successful spawnings were achieved from two of the 13 matings attempted. Hatch rates were low (< 4%) but 85% of the vigorous larvae produced survived to PL1. The hybrid identity of the larvae was confirmed by allozyme analysis at five diagnostic loci. Tank-reared juveniles grew at an overall rate of approximately 0.09 g day−1 to a weight of 10 g in tanks until the prawns were stressed at 4.5 months. A number of viral diseases were expressed subsequently, including IHHNV, and the experiment was terminated. There was no indication of hybrid vigour in growth rates, and the high growth rate of P. monodon was not combined simply with the colour patterns of P. esculentus. A variety of body colour and pattern variants, ranging between those of P. monodon and P. esculentus, was observed in the hybrids.

Growth of Penaeus monodon×Penaeus esculentus tiger prawn hybrids relative to the parental species

Abstract Interspecies hybrids were produced by artificial insemination of Penaeus monodon females with P. esculentus males. Successful spawnings (those in which some eggs hatched) were achieved from nine of the 17 P. monodon × P. esculentus matings attempted (53%). Mean egg numbers produced ranged from 158,000 to 438,000 but hatch rates were low ( −1 ), was the same as those of pure P. monodon (0.047 g day −1 ) and significantly greater than that of P. esculentus larvae (0.033 g day −1 ). The relative growth rate among parental species and the hybrids was determined accurately by rearing progeny of pure and hybrid matings in parallel under controlled conditions. The colour pattern of the hybrids was intermediate between that of P. monodon and P. esculentus . Sex ratio was significantly skewed in favour of males in the hybrids (proportion of males was 0.86 compared with 0.56 in the parental species), possibly suggesting females are the heterogametic sex in penaeids. The hybrids had the fast growth rate of P. monodon , and some of the attractive colour pattern of P. esculentus .

Utility of streamer tags to assess survival and growth of juvenile tiger prawns (Penaeus monodon) in aquaculture environments

Abstract Experiments in tank and pond environments over 5–6 months showed that growth rate of juvenile Penaeus monodon was unaffected by tagging at 15 mm carapace length (CL) or at 18 mm CL. The mortality rate of prawns tagged at 15 mm CL was consistently greater than those tagged at 18 mm CL in both environments, suggesting that the minimum size for tagging to obtain less biased survival estimates is at least 18 mm CL. Survival in the tank of prawns tagged at 18 mm CL was the same as untagged animals (40–50%), but that of prawns tagged at 18 mm CL in the pond (50%) was less than untagged prawns (70%). These results suggest an environment-specific effect on tag-induced mortality: The ability to obtain independent data from untagged animals in aquaculture ponds allowed the effect to be detected. This has been impossible in wild fisheries work and the results in this paper highlight the inadequacy of tagging methods to obtain mortality estimates from wild prawn populations. Tag colour also biased tag recovery rates, but no mechanism to explain the bias was identified. Streamer tags will prove useful in aquaculture as the tags are unlikely to affect important performance characteristics of the marked animals, such as growth rate, and reasonable relative estimates of mortality among tagged groups can be obtained. However, the use of tagged animals to gain accurate estimates of mortality of an untagged group they are meant to represent is unlikely to be successful, even in relatively well-controlled aquaculture situations, because of environment specific effects on tag mortality.