Population Consequences of Releasing Sex-reversed Fish: Applications and Concerns

1. Abstract Sex differentiation is generally more labile in gonochoristic fish than it is, for example, in birds and mammals. Environmentally induced sex reversal is therefore often possible and creates genotype-phenotype mismatches that can be useful in population management. Interestingly, sex chromosomes of fish are typically not significantly decayed, i.e. all types of offspring of sex-reversed individuals may be viable, including YY and WW individuals that can then often be sex reversed again. Releasing sex-reversed fish, or releasing untreated YY and WW offspring of sex-reversed fish, into natural populations can therefore affect sex ratio of the population in the following generations and hence affect population growth. Some types of releases are likely to boost population growth if the number of females are limiting (e.g. WW individuals to create female-biased population sex ratios), others can be used to reduce growth of undesired population (e.g. YY individuals to create male-biased sex ratios). However, these ideas remain still largely untested. Key variables in respective population models are the effects of sex reversal and of unusual karyotypes on viability and reproduction under natural conditions. These key variables need to be determined to allow for data-based models that can serve as basis for field trials.