Sperm Quality of Pond-Reared and Wild-Caught Penaeus monodon in Thailand1

Sperm quality, as determined by visual examination and by reaction with “egg-water” was not significantly different (P > 0.05) for sperm obtained by electro-ejaculation from ablated or non-ablated pond-reared Penaeus monodon. Nor was sperm quality different between pond-reared and wild-caught prawns. Normal sperm, determined by appearance, ranged from 17.1 to 21.0%, while reactive sperm ranged from 1.5 to 3.0%. There were, however, significant correlations (P < 0.01) between spermatophore weight and prawn weight (r= 0.73, N= 434). Male prawns weighing 4150 g produced on average spermatophores weighing 22.7 mg and containing 0.8 million sperm, while prawns weighing 61-90 g produced on average spermatophores weighing 56.6 mg with 2.5 million sperm. Ablation did not increase spermatophore size or sperm quality, although it significantly increased mortality of ablated males. Male prawns could be re-ejaculated at about weekly intervals with no change in sperm quality. Wild-caught female prawns artificially inseminated with spermatophores from electro-ejaculated males produced normal spawns with 51% average egg fertilization, and 41% nauplii hatch success. Nauplii hatch success following spawning increased from >60% for newly inseminated females to near zero after 30 days post-insemination, indicating spermatophore depletion and/or deteriorated sperm quality during spermatophore storage in the thelycum. The findings of the present study indicate that electro-ejaculation and artificial insemination are relatively simple and practical methods for improving captive reproduction performance of closed-thelycum prawns such as P. monodon, and that pond-reared and wild-caught males produced sperm of similar quality.     

Effects of different feeding regimes on ovarian maturation and spawning of pond-reared giant tiger prawn in Thailand

Large pond-reared Penaeus monodon were used in three maturation and spawning trials lasting 60 days. One group of prawns was fed a fresh diet only; a second group was supplied a fresh diet combined with a formulated pelleted diet; a third group of prawns received the formulated diet only. Total maturation (N = 66 and 55) and spawning events (N = 63 and 48) were much greater for prawns receiving only the fresh diet, and the combined fresh with formulated diets, respectively. Prawns receiving only the formulated diet matured only 12 times, and spawned 11 times. Prawns fed a fresh diet produced significantly more eggs than those given a formulated diet alone. No significant differences were seen in eggs produced per spawning event, % fertilization, % hatch or % metamorphosis from egg to protozoea. Female prawns exhibited greater mortality than did males, while females on the fresh diet only had greater mortality than did other females, presumably due to greater handling and other stress factors. Female prawns on a combined diet had lower mortality than other females. The formulated diet used is suitable for supplementation, but not as a sole maturation food.     

Bacterial community composition and distribution in different segments of the gastrointestinal tract of wild‐caught adult Penaeus monodon

Bacterial community associated with the gastrointestinal (GI) tract of aquaculture animals can play important roles in health, nutrition and disease. Compared with the GI tract of aquatic vertebrates such as fish, crustacean GI tract has unique structures and surfaces in different segments that may contribute to differences in the bacterial communities. This study examined the bacterial composition and distribution in different segments along the GI tract and in digesta of wild‐caught adult Penaeus monodon using Automated Ribosomal Intergenic Spacer Analysis (ARISA), real‐time quantitative PCR and clone libraries of 16S rRNA genes. Thirty‐nine bacterial species in four phyla including Proteobacteria (α, β, ε, γ), Firmicutes, Bacteroidetes and Actinobacteria were represented in the GI tract of adult P. monodon. Proteobacteria comprised over 80% abundance of the bacterial community in most segments of the GI tract, except the middle intestine that was dominated by Firmicutes (~50% abundance). The results also showed that bacterial communities showed significant differences along the GI tract segments, particularly the hindgut (p < .001) with Vibrio and Ferrimonas as dominant genera. The knowledge about the distribution of bacteria could be useful in understanding interaction of commensal bacteria and pathogens in different segments, and its potential influence on the effectiveness of probiotic bacteria in the GI tract of shrimp.     

Correction of black tiger prawn (Penaeus monodon fabricius) coloration by astaxanthin

After two months of feeding a group of juvenile black tiger prawn (Penaeus monodon) with a commercial feed (CF), their external pigmentation changed from its normal greenish-brown to a light blue. This condition was thought to be induced by a carotenoid deficiency in the feed. Nutritional improvement and hence correction of this condition was attempted by adding 50 ppm astaxanthin (Roche Ltd^®) into one feed (AF) and 5% addition of brown algae (Chnoospora minima) into a second feed (BF). After four weeks of feeding, the prawns fed on AF reverted to their normal greenish-brown pigmentation. The carotenoids present in the BF feed increased carotenoid content in the prawns, but the levels were not high enough to correct the blue coloration. Analysis of carotenoid content in the shells of the groups showed 318%, 57% and 14% increase for AF, BF, and CF respectively, with 70–90% of the total carotenoid being in the form of astaxanthin. Deposition of astaxanthin was higher in the shell than in the flesh, with deposition in the flesh plateauing after two weeks, whilst deposition in the shell increased steadily.

The importance of these findings to the marketing of cultured shrimps is discussed.     

Effects of Broodstock Size and Source on Ovarian Maturation and Spawning of Penaeus monodon Fabricius from the Gulf of Thailand

The effects of broodstock source (pond-reared and wildcaught from shallow waters) and prawn size (large—weight >120 g, and small-weight < 110 g) on ovarian maturation and reproductive success of Penueus monodon were evaluated. Large females underwent stage IV ovarian maturation and spawned with greater success than did small prawns. Both pond-reared and wildcaught females of the same size exhibited comparable maturation and spawning success. Large females rematured and spawned more frequently than small ones. Total eggs produced by large prawns was significantly greater than for small prawns; nevertheless, prawn source and size had no significant influence on amount of eggs spawned per spawning event. Egg quality varied greatly in terms of percent fertilization, hatch rate, and metamorphosis to first protozwa stage.     

Water quality control using Spirulina platensis in shrimp culture tanks

A cyanobacterium (Spirulina platensis) was co-cultured with black tiger shrimp (Penaeus monodon) for water quality control. We evaluated the effects of: (1) three S. platensis trial conditions on inorganic nitrogen concentrations at one shrimp density (S. platensis trial conditions included: absent, nonharvested and semicontinuous harvesting) and (2) two shrimp densities on inorganic nitrogen concentrations, with and without S. platensis. Semicontinuous harvesting of S. platensis at one shrimp density resulted in significantly reduced (P<0.05) inorganic nitrogen concentrations (NH₄, NO₂ and NO₃). With S. platensis absent, ammonium and nitrite concentrations ranged from 0.5 to 0.6 mg l⁻¹, while nitrate concentrations ranged from 16 to 18 mg l⁻¹ by day 44. With nonharvested S. platensis, considerable variability occurred with nitrogen concentrations. Semicontinuous harvest of S. platensis reduced nitrate to 4 mg l⁻¹, while ammonium and nitrite ranged from 0.0 to 0.15 mg l⁻¹, respectively. The factorial evaluation of shrimp density versus presence and absence of S. platensis resulted in greatly reduced nitrogenous compounds with S. platensis present regardless of shrimp density, and only moderately increased nitrogen with greater shrimp density. Without S. platensis, all nitrogen compounds were substantially elevated and shrimp survived was significantly reduced at high shrimp density.     

Development of methods for detection of SNPs in <Emphasis Type="Italic">Activin type IIB receptor</Emphasis> and a preliminary study on association between its polymorphism and growth parameters of the Asian seabass <Emphasis Type="Italic">Lates calcarifer</Emphasis>

Molecular markers that allow selection of juveniles and broodstock with a high growth performance are useful for the aquaculture industry. In this study, association between single nucleotide polymorphisms (SNPs) of the Activin type IIB receptor (LcActRIIB) and growth-related parameters of Asian seabass Lates calcarifer juveniles were examined by PCR-direct sequencing. Three SNPs (G>A_c.965+g.7, C>A>T _c.965+g.33 and G>A _c.965+g.189) generating seven composite SNP genotypes (diplotypes) were found in the LcActRIIB gene segment (398 bp). Among three identified SNPs, only a G>A_c.965+g.7 SNP showed significant association with growth traits (average body weight, total length, hepatic weight and hepatosomatic index) of examined fish (P < 0.01). Significant association between diplotypes and growth-related parameters were found. Juveniles exhibiting diplotypes I–V showed greater growth-related parameters than those exhibiting diplotypes VI (P < 0.001; N = 57). Simple methods for rapid genotyping of a G>A_c.965+g.7 SNP were successfully developed based on gel-based bi-allelic PCR amplification of specific alleles (Bi-PASA) and real-time PCR-based PASA analyses (N = 99). Identical genotypes were consistently obtained from different detection methods.