Effects of high temperature exposure on early reproductive development in monosex female sablefish (Anoplopoma fimbria)

Abstract

Aquaculture supplies over half of all seafood produced for human consumption. However, production processes are raising environmental concerns, and escapement of farmed fish is a prominent issue. A viable solution is to produce reproductively sterile fish so escapees cannot genetically contaminate wild populations. For this study, we examine high temperature treatment as a method for achieving sterility since it is shown to induce germ cell loss in some female fishes. Monosex female sablefish larvae (~30 mm in fork length; ~90 days post-fertilization) were randomly divided into three groups and exposed to different temperatures, control (15°C), moderate (20°C), or high (22°C), for 19 weeks. During this time, larvae were periodically sampled for paraffin histology and gene expression analysis from each treatment group to assess gonadal development. After the treatment period, remaining fish were tagged and transferred to ambient temperatures for one year to determine whether temperature effects were maintained post-treatment. We found that exposure to elevated temperatures induced severe impairment of early ovarian development. Sablefish at moderate and high temperatures had significantly less developed oocytes relative to controls, and germ cell-specific genes and apoptosis-related genes indicated germ cell degeneration. However, after one year at ambient temperatures, impaired gonads were no longer observed and most high-temperature treated fish had ovaries similar to those of controls. We also observed two sex-reversed females (female genotype but male phenotype), referred to as neomales, from the high temperature group which opens the possibility of using high temperature for future neomale broodstock production. Neomale broodstock are a key component for monosex sablefish production, and being able to generate them via high temperature may represent an improvement upon current methodology. Based on these results, we conclude that high temperature is likely not an effective method for inducing reproductive sterility but may be a preferable method for neomale production in sablefish.