Physiological factors affecting triploid production in rainbow trout, Oncorhynchus mykiss

The influence of three physiological factors related to triploid production was examined for rainbow trout. Individual spawnings of 46 females were used to perform triploid production experiments from 1989 to 1991, with various water temperatures (6-13.8°C) at stripping and egg incubation. The percentage of triploids was similar for a heat shock of 26.5°C for 15 min applied 15 or 25 min after fertilization (73.4±5.6% vs 78.6±4.5%). A tendency to a higher percentage of triploids (85.9±5.7%) was observed for water temperatures of 6-8.0°C at stripping and incubation, compared to at higher water temperatures of 12.1-14°C (63.0±8.4%). Analysis of variance indicated an effect of four categories of water temperature (6-8, 8.1-10, 10.1-12, 12.1-14°C) on triploid product at P = 0.14. Regression analysis confirmed these as significant (r = -0.36; P < 0.02). A significant increase in percentage of triploids was observed when eggs remained 2, 6 and 10 days in the body cavity. The mean % triploid

Chromosomal characterization of cultured populations of Chilean coho salmon (Oncorhynchus kistuch)

Chromosomal characterization of coho salmon samples from three fish farms in southern Chile (Polcura, Castro and Coyhaique) was carried out in order to compare their chromosome constitutions. All populations had a 2n = 60; however, Polcura and Coyhaique had a different chromosome arm number (NF = 110; 40m + 10sm + 10st/t) than Castro (NF = 108; 40m + 8sm + 12st/t). Variation in NF was due to chromosome pair 25, which was submetacentric in Coyhaique and Polcura, but subtelocentric in Castro. In all karyotypes, a large submetacentric chromosome pair exhibited an interstitial secondary constriction in the short arm. The observed variability in chromosome arm number agrees with previous reports for O. kisutch, and in this particular case it seemed to be caused by a pericentric inversion of pair 25. Cultured populations of Chilean coho salmon are, therefore, likely to be cytogenetically variable.<br>A caracterização cromossômica de amostras de salmon tipo coho de três criações de peixes do sul do Chile (Polcura, Castro e Coyhaique) foi feita com a intenção de comparar suas constituições cromossômicas. Todas as populações apresentaram 2n = 60; contudo, Polcura e Coyhaique tiveram um número de braços cromossômicos (NF = 110; 40m + 10sm + 10st/t) diferente de Castro (NF = 108; 40m + 8sm + 12st/t). A variação no NF deveu-se ao par cromossômico 25, que era submetacêntrico em Coyhaique e Polcura e subtelocêntrico em Castro. Em todos os cariótipos, um grande par cromossômico submetacêntrico exibiu uma constrição secundária intersticial no braço curto. A variabilidade observada no número de braços cromossômicos concorda com relatos prévios para O. kisutch e, neste caso particular, parece ter sido causada por uma inversão pericêntrica no par 25. Portanto, populações cultivadas de salmão chileno do tipo coho provavelmente são citogeneticamente variáveis