Asian Program

Japanese

Data

Former Fellows

Dissertation Abstracts

Thailand

  The MekongRiver Basin is one of the most biologically diverse inland water systems in the world, and is the home of some 1,200 fish species. The seven-line barb is one of the most important indigenous fish of the MekongBasin and is considered as a flagship species in the content of conservation. It has been classified as endangered on the IUCN Redlist since 1996. In Thailand, the fish is found in MaeKlongRiver in the western part and in the MekongRiver in the northeastern part of the country. However, natural populations have been extirpated from the MaeKlongRiver and can be expected to disappear as more impoundments are constructed in the Mekong. At present, it is not known whether the fish that occur in various parts of the MekongRiver are genetically the same or not. Therefore, it is urgently important to develop the breeding technique and examine the genetic diversity of seven-line barb in order to develop a management plan to improve the situation of the species.
  Studies on induced spawning of the Thai carp, Barbonymous gonionotus, indicated that the gonadotropin (GtH) secretion and spawning induction in tropical cyprinids is regulated by a dual control of gonadotropin releasing hormone and dopamine. The use of Gonadotropin releasing hormone analog (GnRHA) in combination with a dopamine antagonist such as domperidone (DOM) has proven to be very effective in spawning induction in the Thai carp. This technique was used to develop breeding technique in seven-line barb. The result showed that using Buserelin (BUS), a mammalian GnRHA, in combination with DOM alone was not as effective as using pituitary gland (PG) or using two injections of BUS+DOM and PG. Additional of gonadoplex (GDP), a mammalian GtH, could not increase the effectiveness if PG was sufficiently given. The most effective method for induced ovulation of the seven-line barb was to use two injections of 10 µg/kg BUS+10 mg/kg DOM for the first injection and 6 hrs after, 1.5-2.5 dosages of PG. Furthermore, multiple injections of the mature female with 500 IU/kg hCG to increase its oocyte diameter to >1.7 mm follow by two injections of BUS in combination with DOM was found to be the most potent technique for inducing spawning of captive seven-line barb.
  Microsatellite DNA markers for seven-line barb were developed from the wild caught samples using (GT)15 probe. The number of alleles per locus ranged from 7 to 16. The expected heterozygosities ranged from 0.47 to 0.91. Also, these primers were successfully amplified in the two closely related species, P. labeamajor and P. labeaminor. These markers have proven to be very useful for the population genetic structure study in this species and other related cyprinids.
  Genetic diversity of seven-line barb was investigated using 6 msDNA markers and sequencing analysis of mitochondrial DNA control region (mtDNA). Both msDNA and mtDNA showed concordant results in demonstrating similar genetic diversities and population structuring of seven-line barb. Furthermore, genetic diversity of seven-line barb was quite high compared with other endangered fish species reported to date. Population sub-structuring of seven-line barb was also observed which was no evidence for isolation by distance and no apparent physical barriers. The results suggested that the number of populations of seven-line barb may be determined by the number of geographic setting within which their life cycle can be completed. For management point of view, it is proposed that all populations should be directed toward preserving the genetic integrity of each group.
  Genetic diversity within and between hatchery populations of seven-line barb was compared with those of wild populations using 5 microsatellite DNA markers (msDNA) and sequencing analysis of the mitochondrial DNA control region (mtDNA). Both msDNA and mtDNA markers showed comparable results in demonstrating similar genetic diversities of seven-line barb. Marked reductions of genetic variability in the hatchery populations compared with the wild populations were observed in term of both msDNA number of alleles and mtDNA haplotypes. FST and FST also suggested that the magnitude of the genetics divergence within and among wild and hatchery populations of seven-line barb was significant. The lower genetic variability observed in the hatchery populations may cause by bottleneck effect due to the limited number of effective parents when each population was founded. Enhancing genetic variability and eliminating the accumulated effect of inbreeding of hatchery populations by means of increasing effective population size, preventing inbreeding and using selective breeding based on the principle of minimal kinship broodstock management is recommended to minimize genetic impacts of restocking program.
  The effectiveness of the minimal kinship (MK) selective breeding and random breeding on preservation of genetic diversity of the hatchery populations of seven-line barb was compared. The results indicated that the minimal kinship, calculated by Psa values (MKp) based on 5 msDNA markers yielded a better result in retaining the loss of HE and AE than the random selection. For HE, the differences of both approaches were prominent when the number of parent used in each generation was more than 10 pairs. Further, the loss of HE significantly decreased when the number of parent increased (Kruskal Wallis test, p<0.05). The MKp approach could increase about 6.4% of HE within 30 generations when at least 100 parents were used and 500 offspring were kept in each generation. On the other hand, the MKp selective breeding showed a better result in retaining the loss of AE only when the number of parent was at 100 pairs. MKp selective breeding approach could conserve about 80% of AE for 30 generations when at least 500 offspring was kept (O=500) and 100 parents (P=100) were used as breeders in each generation. Furthermore, if the number of parent was set at 100 individuals, inbreeding will not occur in the MKp selective breeding approach. For preserving genetic diversity of seven-line barb, it is recommended to use minimal kinship selective breeding approach which uses 100 parents and keep 500 offspring in each generation.
  From the results, the conclusion and recommendation on broodstock management of seven-line barb are as follow:
  Because the seven-line barb in the MekongRiver exhibits the genetics divergence according to their spawning grounds, each population could be considered as "Management Units". All population should be directed towards preserving the genetic integrity of each group.
  Since the genetic diversity of hatchery populations was different from the wild population, it should not be used for restocking. Captive broodstock used for restocking program should be founded by collecting fish from the wild populations, and the offspring should be released back into natural habitat from which the founders were derived. These broodstock could still be used for seed fish production of genetically improved by selective breeding on important traits being important for efficiency on growing, survival, and palatability for aquaculture purpose.
  Breeding of the seven-line barb should be done by using minimal kinship selective breeding approach in order to retain genetic diversity of the captive stock.
  Induced spawning of seven-line barb should be done using multiple injections with hCG to increase the oocyte diameter to > 1.7 mm follow by 2 injections of BUS and DOM. Genetic variability of seed fish should be examined before restocking and/or aquaculture used.
  Genetic diversity of both wild and hatchery populations should be monitored regularly in order to assess the success of its management plan.