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Abstract: A broodstock management plan was designed for the world''s biggest catfish, the critically endangered Mekong giant catfish (MGC), Pangasianodon gigas, based on multilocus genotypes of seven microsatellite loci. The broodstock included a total of 129 pit-tagged mature MGC from seven farms in Thailand covering approximately five year-classes. The genetic variation within stocks was relatively low (number of alleles/locus=2.29±0.76–4.00±1.83; effective number of alleles/locus=1.84±0.51–3.04±1.04; H o =0.58±0.34–0.80±0.12; H e =0.43±0.21–0.66±0.11). The genetic relatedness (r xy : [Ritland, K., 1996. Estimators for pairwise relatedness and individual inbreeding coefficients. Genet. Res. 67, 175–185.]) was used to identify the unrelated pairs wherein a minimum value of r xy for half-sib family (r xy =0.07) was considered as a critical value of unrelatedness. The average r xy within farm (0.21±0.13–0.31±0.07) was relatively high compared to the overall average r xy (0.20±0.01), suggesting collaborative broodstock management among farms should be carried out in future. In the short-term six scenarios were proposed based on the 28 and 63 mature male and female brooders, respectively. The results suggest that the best strategy for maintaining the genetic diversity while minimizing inbreeding of MGC was to select mating pairs based on the r xy . A long-term management plan simulation using the BOTTLESIM program showed that if a random mating scheme is adopted N e should be kept at 100 in order to preserve>90% A for four generations (120 years). Applying the mk (minimal kinship) selection for only the first generation can reduce N e to >30 individuals and can retain >90% A throughout the same period. [Copyright &y& Elsevier]

For the long-term preservation of the genetic resources of endangered fish species, a combination of germ cell cryopreservation and transplantation can be an effective technique. To optimize these techniques, it is important to identify undifferentiated germ cells possessing transplantability, such as primordial germ cells, type A spermatogonia (ASGs), and oogonia. In this study, a homolog of vasa cDNA in Mekong giant catfish (MGC- vasa) (Pangasianodon gigas), which is an endangered species inhabiting the Mekong river, was cloned and characterized for use as a putative germ cell marker. Results indicate that MGC-Vasa contained all of the consensus motifs, including the arginine–glycine and arginine–glycine–glycine motifs, as well as the nine conserved motifs belonging to the DEAD-box family of proteins. Results from phylogenetic analysis indicated MGC-vasa also grouped with Vasa and was clearly distinguishable from Pl10 in other teleosts. Results from analysis of abundance of mRNA transcripts using reverse transcription-polymerase chain reaction and in situ hybridization performed on immature Mekong giant catfish testis indicated vasa was present specifically in germ cells, with large abundances of the relevant mRNA in spermatogonia and spermatocytes. Sequence similarity and the specific localization of MGC- vasa in these germ cells suggest that the sequence ascertained in this study was a vasa homolog in Mekong giant catfish. Furthermore, vasa -positive cells were detected in prepared smears of testicular cells, indicating that it may be a useful germ cell marker for enzymatically dissociated cells used for transplantation studies. • A homolog of the vasa gene in Mekong giant catfish (MGC- vasa) was characterized for use as a germ cell marker. • The MGC- vasa contained all of the consensus motifs belonging to the DEAD-box protein family. • MGC- vasa mRNA was specifically detectable only in ovary and testes. • The MGC- vasa gene was expressed only in the germ cells, with a strong expression in the spermatogonia. • The vasa -positive cells could be detected in spermatogonial stem cell-like cells of testicular germ cells. [ABSTRACT FROM AUTHOR]

The larviculture of Mekong giant catfish (Pangasianodon gigas, Chevey 1930) solely relies on live feeds.This study aimed to investigate the proper time to replace live feeds with a microcapsule diet (MC diet) in the earliest stage of larvae to reduce dependency on live feeds in larval rearing of Mekong giant catfish. Crude enzyme of the 3-dph (days post hatching), 7-dph, 14-dph, and 30-dph larvae were extracted for determination of proteolytic digestive enzyme activities. Specific activities of total protease, chymotrypsin-like and trypsin-like of larvae displayed an elevated tendency with increasing life stage of larvae. The highest specific activities of all digestive enzymes were noticed at 30 dph (p < 0.05). In vitro protein digestibility of fish protein hydrolysate (FPH) and fish meal digested by different-stage larval extracts showed that protein digestibility of both ingredients significantly increased with increasing life stage of the larvae (p < 0.05). Protein digestibility of FPH was significantly higher than that of fish meal at 3 dph, 7 dph, and 14 dph (p < 0.05). The highest protein digestibility of both ingredients were statistically observed in 30-dph larvae (p < 0.05). The results of in vitro experiments indicate that the metamorphosis of digestive system of larvae, which begins after 14 dph, is a suitable time to firstly introduce an inert diet for this catfish larval nursing. In a 28-day feeding exper TITLE \* MERGEFORMAT iment, 15-dph catfish larvaewere fed under three different feeding regimes including: Group A (live feed as a control) hand fed with Moina spp. from 15 dph to 42 dph; Group B (Moina and then MC diet) fed with Moina as a live feed and then MC diet from 15 dph to 27 dph and switched to MC diet as an inert diet from 28 dph to 42 dph; and Group C (MC diet) fed with MC diet from 15 dph up to 42 dph. They were fed three times daily for 28 days. The results showed improvement in weight gain rate and specific growth rate of catfish in Group B were comparable to that Group C fed with MC diet alone (p < 0.05). No significant difference in survival rate among the treatments was found (p > 0.05). Feeding MC diet did not cause any histopathological alterations in liver and intestine of catfish. In conclusion, early introduction of catfish larvae with MC diet alone can start at 30 dph, which helps in shortening Moina feeding period, providing growth rate and survival rate benefits. • Transition of endogenous to exogenous feeding in Mekong giant catfish larvae begins about 3 dph. • Metamorphosis of digestive system of catfish larvae onsets after 14 dph. • Digestive system becomes fully functioning for protein digestion at 30-dph stage • Feeding of MC diet to Mekong giant catfish larvae should be performed at 28 dph. [ABSTRACT FROM AUTHOR]