Peter J. Crocos

Genetic mapping of the kuruma prawn Penaeus japonicus using AFLP markers

Abstract Amplified fragment length polymorphism (AFLP) analysis is a rapid, efficient technique for detecting large numbers of DNA markers for linkage analysis. We have used AFLP markers in a two-way pseudo-testcross strategy to generate genetic maps of a Penaeus japonicus family. A two-stage selective genetic mapping strategy was applied in this study. The initial stage involved the linkage mapping on 46 progeny from two tails (top and bottom 6%) of the size distribution of an intermediate cross family (F1 from HH×LL and F2 from HL×LH) using 54 pairs of AFLP primer combinations. The second stage of linkage mapping involved genotyping an additional 56 progeny (top and bottom 8%) of the same family with the same 54 primer combinations based on the framework map from the first stage. Of 535 polymorphic fragments scored in 46 progeny of the first stage, 355 segregated in a 1:1 ratio, corresponding to DNA polymorphisms heterozygous in one parent and null in the other. The other 154 markers followed a 3:1 Mendelian segregation ratio. Of 502 bands scored in 56 progeny of the second stage, 359 segregated in a 1:1 ratio and 138 in a 3:1 ratio. When the markers with a 1:1 segregating ratio were combined from both stages (401 in total), 217 markers were ordered into 43 linkage groups (1780 cM) of the paternal map and 125 markers in 31 linkage groups (1026 cM) of the maternal map. The average density of markers was approximately 1 per 10 cM. To investigate the homologies between two parental maps, we included 182 markers segregating 3:1 in the analysis. One homologous linkage group was recognised. The sex marker initially mapped on the maternal parent map was also confirmed in the second-stage mapping with more progeny information. The linkage data developed in these maps will be used to detect loci controlling commercially important traits.

Response to selection and heritability for growth in the Kuruma prawn, Penaeus japonicus

Abstract Divergent selection for High (H) and Low (L) growth was carried out for a single generation with the aim of measuring response to selection and heritability of growth in Penaeus japonicus . H and L growth (weight at 6 months of age) parents were selected from a commercial prawn pond which had been stocked with post-larvae from wild caught broodstock. Offspring of H×H, L×L and reciprocally mated (H×L, L×H) parents were reared and grown out in laboratory tanks. The direct response to one generation of selection averaged 10.7%, being 8.3% for high growth and 13.1% for low growth. Responses at other ages averaged 5.7, 6.9 and 7.9% at 3, 4 and 5 months, respectively. The average realised heritability for weight at 6 months of age was 23.4% which did not differ significantly from the estimate from the regression of offspring on mid parent of 27.7% It was concluded that the heritability of growth in P. japonicus is moderate but that rates of response to selection will be high largely due to the high levels of natural variation.

Seasonal and age variability in the reproductive performance of Penaeus semisulcatus broodstock: optimising broodstock selection

Abstract The knowledge of the inherent reproductive patterns of wild prawn (shrimp) populations is essential in predicting the expected performance of hatchery broodstock. In response to problems of variable hatchery performance of penaeid broodstock at some times of the year, the inherent seasonal variability and the effects of broodstock age on reproductive performance of Penaeus semisulcatus were examined. The investigation of these effects, using a penaeid for which the detailed reproductive ecology was well known, provided a proxy from which to describe the general case likely applicable to other farmed species. During the three-year study, assessments were made for broodstock of known but increasing age collected from the wild overall seasons (at 2-monthly intervals), and from the two distinct age-cohorts present in the same season. The reproductive performance of the broodstock was assessed at each stage of the maturation and spawning process. Measures of maturation rate, spawning rate, fecundity, hatch rate, larval survival rate, and larval production rate were obtained. Inherent temporal patterns in the measures of reproductive performance were found for the main annual cohort of the wild stock. The rates of spawning, egg production, nauplii production and protozoeae production were lowest in autumn when females were 6 months old, increased through to a spring peak (at 12 months old), and then declined by early summer by which time females were 14 months old. Broodstock survival, egg hatching and metamorphosis of nauplii to protozoeae were unaffected by time of year. Trials with two age-cohorts present in the same season enabled us to separate the effects of age and season. Twelve-month-old broodstock outperformed 6-month-old broodstock, regardless of season. Age was the best predictor of reproductive performance. An optimal age of 12 months for best reproductive performance was identified. This information can be used to select broodstock for hatchery production. The findings may be applicable to other species of farmed penaeids.

Maturation and spawning of the banana prawn Penaeus merguiensis de Man (Crustacea: Penaeidae) in the Gulf of Carpentaria, Australia

Abstract Investigation of the reproductive cycles of female Penaeus merguiensis de Man in the Gulf of Carpentaria showed that maturation of ovaries from the stage of vitellogenesis (Stage III) to the ripe condition (Stage IV) and subsequent spawning occur during a single intermoult period. The sequence of events in reproductive and non-reproductive moulting cycles are described. Fecundity varied from ≈100 000 to 450 000 eggs for individuals of 28 to 45 mm carapace length, respectively. Investigation of spawning seasons and spawning areas was based on the use of an index of population fecundity so that the effects of abundance of a spawning population and the relative contribution of various sizes of spawning females on overall egg production could be considered. Spawning occurred generally over the range of the adult distribution with a tendency for more spawning activity in deeper waters. Egg production was markedly seasonal. Greater egg production occurred during spring and autumn in both the southeastern Gulf and the Weipa area, with a dominant autumn peak in the southeastern Gulf and a dominant spring peak at Weipa. Peaks of spawning activity in the Cape Keerweer area were in August, January and April. Maximum peaks of reproductive output do not forecast maximum recruitment of postlarvae to the estuary systems in each area. Possible explanations for this are discussed.

The effects of temperature on the growth, survival and biomass of different families of juvenile Penaeus japonicus Bate

Variation in the growth, survival and change in total biomass (termed biomass increase) of different families of juvenile Penaeus japonicus was investigated over a range of temperatures in controlled laboratory experiments. In the first experiment, the effects of temperature on six families of juveniles were examined over a broad range of temperatures (24 to 30 degreesC). In the second experiment, the effects of temperature on six more families of juveniles were examined over a narrower range of temperatures (27.5 to 31.2 degreesC). Over the broad temperature range, mean growth and biomass increase were highest at 27 degreesC and mean survival was highest at 24 degreesC. Mean growth was lowest at 24 degreesC, whilst survival and biomass increase were lowest at 30 degreesC. However, there was a significant interaction between family and temperature, with some families tolerating a broader range of temperatures than others. As a result, the ranking of families in relation to growth, survival and biomass increase changed at each temperature. This effect was more pronounced for survival than for growth. Over the narrower range, temperature significantly affected growth, survival and biomass increase, but there was no significant interaction between family and temperature. Growth, survival and biomass increase were significantly lower at 31.2 than at 27.5 and 29.2 degreesC. These results suggest that if grow-out conditions for P. japonicus vary by more than a few degrees, interactions between family and temperature could affect the efficiency of selection. The results also suggest that the family x temperature interaction may have a more pronounced effect on survival than on growth. Crown Copyright (C) 2002 Published by Elsevier Science B.V. All rights reserved.

The effects of density on the growth and survival of different families of juvenile Penaeus japonicus Bate

Variations in the growth and survival of six families of juvenile (initial mean weight = 4.16 g) Penaeus japonicus were examined at two densities (48 and 144 individuals m(-2)) in a controlled laboratory experiment. Survival was very high throughout the experiment (95.4%), but differed significantly between densities and rearing tanks. Family, sex and family x density interaction did not significantly affect survival. Mean specific growth rate (SGR) of the shrimp was 18% faster at the low density (1.93 +/- 0.05% day(-1)) than at high density (1.64 +/- 0.03% day(-1)). However, there was a small but significant interaction between family and density indicating that growth of the families was not consistent at both densities. The inconsistent growth of the families across the two densities resulted in a change in the relative performance (ranking) of families at each density. Sex, rearing tank and rearing cage also affected growth of the shrimp. Mean SGR of the females (1.79 +/- 0.03% day(-1)) was 5% faster than males (1.70 +/- 0.03% day(-1)) when averaged across both densities. Shrimp grew significantly faster in rearing tank 3 than rearing tank 1 or 2 at both densities. Results of the present study suggest that family x density interaction could affect the efficiency of selection for growth if shrimp stocks produced from shrimp breeding programs are to be grown across a wide range of densities. Crown Copyright (C) 2004 Published by Elsevier B.V. All rights reserved.

Factors affecting induction of maturation and spawning of the tiger prawn, Penaeus esculentus (Haswell), under laboratory conditions

Abstract Adult tiger prawns, Penaeus esculentus , were held under varying conditions of temperature, photoperiod and tank size for assessment of ovarian maturation and spawning. Both eyestalkablated and unablated females were studied. Maturation and spawning of unablated females was favoured by conditions of warm temperature (26°C) and long days (14.5 h), whereas ovarian maturation did not occur at lower temperature (20°C) and short days (12 h). Tank size was a critical factor with unablated females, as maturation and spawning occurred in a large tank (3.2 m 2 , 0.9 m depth) but did not occur in small tanks (1 m 2 , 0.3 m depth) despite favourable temperature and photoperiod conditions. Ablated females matured under both short-day, low-temperature conditions and in small tanks, but the success rate was greater with long days and warm temperatures in large tanks. Ablated females showed ovarian maturation during the second intermoult period after ablation, but unablated females required three or four intermoult periods of the appropriate environmental treatment before onset of maturation. Successful mating was rare in small tanks, but occurred frequently in large tanks.

Effect of age on the consecutive spawning of ablated Penaeus semisulcatus broodstock

The effect of broodstock age on the consecutive spawning performance of wild-caught ablated Penaeus semisulcatus females was assessed for four age groupings (6, 8, 12, 14 months old). Age groupings were determined from time series size data (carapace length measurements) of the broodstock population. Spawning performance of the four age groupings was assessed in terms of the percentage of females spawning, eggs per spawning and hatch rates per spawning. The percentage of females spawning decreased more rapidly over consecutive spawnings for the 14-month age grouping than for the three younger age groupings. Additionally, a smaller percentage of the 6-month-old females spawned than 8- or 12-month-old females across all consecutive spawnings. The number of eggs produced per spawning declined with consecutive spawnings from the older spawners (12 and 14 months old), but not from the younger spawners (6 and 8 months old). The hatch rate did not decline with consecutive spawnings from any of the four age groupings, although the overall mean hatch rates were lower for the 6-month-old females than the older females. These results suggest that broodstock age (and/or size) affects the consecutive spawning performance of P. semisulcatus. Consequently, the reproductive performance expected from ablated shrimps over time in a hatchery may differ depending on the age of the broodstock.

Commercial grow‐out performance and cost‐benefit analysis for farm production of the brown tiger shrimp Penaeus esculentus.

Abstract The brown tiger shrimp Penaeus esculentus is a valuable Australian shrimp species which has aquaculture potential as an alternative species for commercial culture. Commercial grow‐out of P. esculentus demonstrated that this species can be grown to a marketable size in a period well within the conventional grow‐out season for Australian shrimp farms. A bioeconomic model was developed to quantify the economic feasibility of commercial production of P. esculentus relative to the more commonly farmed species Penaeus monodon. The cost‐benefit analysis supports the potential of P. esculentus to be grown with similar profitability to P. monodon, although farm trials oí P. monodon production resulted in a higher profit per ha A scenario analysis was used to identify the critical values of several parameters that would make P. esculentus as profitable as P. monodon. Importantly, the inherently slower growth rate of P. esculentus compared to P. monodon is compensated for by the better prices received by P. esculentus. A 5% increase in growth for P. esculentus would generate equal profitability. This growth improvement could be achieved through selective breeding or further development of a specific P. esculentus diet The outcome of this analysis confirms the potential for P. esculentus to be cost‐effectively grown as an additional species by Australian shrimp farmers.