High prevalence of skeletal deformity and reduced gill surface area in triploid Atlantic salmon (Salmo salar L.)

The prevalence of skeletal deformity throughout the development of different populations tall-female triploid, mixed-sex triploid, all-female diploid and mixed-sex diploid) of Tasmanian Atlantic salmon (Salmo salar L.) was determined to elucidate the possible effects of ploidy or sex status on the incidence of deformity. Populations were produced and maintained under commercial conditions in freshwater until individuals had attained a wet weight of approximately 80 g, at which time each population was divided and either retained in freshwater (FW smelt) or transferred to seawater (SW smelt), where fish were held for a further 2 months. Whole fish were sampled throughout this period from hatching (470 degrees days post-fertilisation). The prevalence of skeletal deformities was significantly higher in triploid populations. Jaw deformity, including lower jaw deformity syndrome (LJD), occurred in up to 2% of triploid fry, 7% of triploid FW smelt. 14% of triploid SW smelt and 1% of diploid FW smelt. The prevalence of LJD was highest in triploid FW smelt. Short opercula were observed in up to 22% of triploids and 16.6% of diploids. Up to 60% of triploids and 4% of diploids suffered from the absence of primary gill filaments (gill filament deformity syndrome (GFD)) during FW development prior to SW transfer, then, up to 50% Of triploid FW smelt and 60% of triploid SW smelt suffered from GFD. There was no significant difference in the sex ratio of each deformity type. An index of gill surface area (GSA) was significantly reduced in normal triploids and triploids afflicted with GFD, compared to diploid counterparts. It is likely that the reduction of GSA affects an individual's capacity for metabolic gas exchange under vigorous exercise or suboptimal environmental conditions. (C) 2001 Elsevier Science B.V. All rights reserved.