A non-invasive method based on head morphology to sex mature three-spined Stickleback (Gasterosteus aculeatus) in rearing conditions
Abstract
The threespine stickleback (Gasterosteus aculeatus) is a small-bodied teleost fish which is a major component of shallow water food webs in the northern hemisphere. G. aculeatus is a reference species for experimental studies, in particular for the assessment of endocrine disruptors. Sex ratio can bias the outcomes of an experimental study, especially if this study focuses on reproduction or behaviour. Moreover, sex-ratio, by itself, can be a very relevant endpoint in experimental tests. A mathematical model to distinguish mature female and male three-spined Sticklebacks G. aculeatus is proposed. This method is based on sexual dimorphism in the head morphology. The discrimination was established on five distances of interest on the head, divided by the standard length of fish. The parameters were estimated based on a training set composed of 102 fish and characterised by an equilibrate sex ratio and validated on a test set composed of 69 fish. Our model permits to balance between the percentage of fish that can be sexed and the percentage of fish correctly sexed. Compared to other available methods to sex G. aculeatus, our model is non invasive, not expensive, rapid, replicable, and can be calibrated out of the breeding period.