National Committee on Marine Sciences (NCMS)
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- Inbreeding levels in selected populations of rainbow trout, Oncorhynchus mykissPante, Ma. Josefa R.; Gjerde, Bjarne; McMillan, Ian (Elsevier BV, 2001-01)Inbreeding levels in three nucleus breeding populations of rainbow trout (Oncorhynchus mykiss) under selection for six generations were investigated. The inbreeding levels across generations as estimated from pedigree information (Pi) and effective population size (Ne) with the assumption of no selection and random mating, among the three populations were all at 11.3% or less. The levels of inbreeding estimated from Ne were generally lower than those calculated from Pi, except in the initial generations. The average rates of inbreeding (ΔF) calculated from Ne and Pi were 0.99% and 2.00%, respectively, for population 1; 0.90% and 0.53%, for population 2; and 0.72% and 1.38%, for population 3. These rates of inbreeding correspond to Ne of 50 and 25, for population 1; 55 and 94, for population 2; and 70 and 36, for population 3. These rates were within the acceptable range 2% to 0.2%, corresponding to Ne of 31 to 250 for avoiding loss of fitness as suggested by Meuwissen and Woolliams [Meuwissen, T.H.E., Woolliams, J.A., 1994. Effective sizes of livestock populations to prevent a decline in fitness. Theor. Appl. Genet. 89, 1019–1026.]. A large proportion of individuals had inbreeding coefficients (F) greater than zero across generations for each population but the individual F were generally below 12.5%. The occurrence of inbreeding can be detrimental to populations undergoing artificial selection. Therefore, the F levels reported here should be followed-up by a study on the impact of inbreeding on important performance traits in rainbow trout.
- Strain differences in cultured fish — Isozymes and performance traits as indicatorsMacaranas, J.; Fujio, Y. (Elsevier BV, 1990-03)A comparison of genetic changes in broodstocks or strains of five cultured fish species, namely, Japanese char, Nile tilapia, Mossambica tilapia, Japanese common carp, and the guppy, showed them to be influenced by the intensity of selection pressure and/or by the history of culture. Allele distributions at polymorphic loci were mainly governed by genetic drift and also by introgressive hybridization or gene exchange. Such genetic changes are expected to occur also at loci controlling performance traits. Using the guppy, Poecilia reticulata, as a model fish, 10 different strains consciously selected for body colour patterns, body size, and finnage, and which were genetically differentiated into six race level groups, were investigated for strain differences in eight growth-related and reproductive traits. Strain differences were significant for all traits and phenotypic differences, expressed as [d]m='P1 - P2||(P1 + P2), were significant in at least one out of eight traits for every strain pair. Of the eight quantitative traits, survival at Day 60, fertility ratio, and brood size showed higher variation, as seen from their coefficients of variation and [d]m range. The correlation of overall [d]m between strains and their corresponding Nei's genetic distance was low (r = −0.104) but individual trait correlations with Nei's D were significant for survival at Day 0 and male body length at Day 60. Results suggest that strain differences are characterized by a random segregation of alleles both at biochemical and trait loci but that occasionally, linkage may occur. The utility of isozyme markers and [d]m the index are discussed.
- Genetic improvement of farmed tilapias: Biochemical characterization of strain differences in Nile tilapiaMacaranas, Julie M.; Agustin, Liza Q.; Ablan, Ma. Carmen A.; Pante, Ma. Josefa R.; Fukushima, A.; Pullin, Roger S. V. (Springer, 1995-03)Four African wild strains (Egypt, Ghana, Senegal and Kenya) and four established Asian farmed strains of Nile tilapia, Oreochromis niloticus (popularly known in the Philippines as ‘Taiwan’, ‘Thailand’, ‘Singapore’ and ‘Israel’) were analysed electrophoretically at 30 protein loci to estimate genetic differences among the strains. All strains shared alleles at 14 monomorphic and 16 variable loci. Among the African strains, characteristic allele frequency differences were observed at AAT-1 * 46 for Ghana and Senegal, ADH * 83 for Kenya, ADH * 120 for Senegal, G3PDH-2 * 300 for Egypt, IDDH * 67 for Senegal, sMDH-1 * 120 for Kenya and SOD * 150 for Senegal. Genetic distance values among the strains revealed a clustering of the farmed strains with Egypt and Ghana O. niloticus, a slight separation of the Senegal strain and a larger separation of the Kenya strain. This profile may reflect the origins of the few founder populations of this species previously introduced to Asia. It also confirms the wider genetic divergence of the Kenya strain (O. niloticus vulcani) from the others studied here, which are all O. n. niloticus. Observed heterozygosities of the strains ranged from 0.026 to 0.071, with the African wild strains the lower values (mean Ho = 0.036) and the farmed strains the higher ones (mean Ho = 0.056). The implications of these results to the ongoing tilapia genetic improvement programme in the Philippines are discussed.