Ultrasonography as a non-invasive technique to assess the effects of diet on the ovaries of female European seabass (Dicentrarchus labrax).

Broodstock management in aquaculture aims to optimise larval production to meet farm demand, which requires precise monitoring of the reproductive cycle. Traditional methods such as histology often require killing of fish, making them unsuitable for monitoring reproductive dynamics at fish level. This study evaluates ultrasonography as a non-invasive tool for describing ovary size dynamics in European seabass (Dicentrarchus labrax). We monitored 48 females fed with different feed amounts with ultrasounds along an entire reproductive cycle, to assess the effect of feed intake on ovarian development. The ovary volume estimated with ultrasounds has been found to be highly correlated with ovary weight (r2 = 0.94, n = 36). The temporal dynamics of ovary size were modelled using a Bayesian approach, revealing relevant between-individual variability in maximum ovary weight, timing and duration of ovarian development. Results indicate that individual, but not cage-level, food intake significantly affects maximum ovary size [slope = 11.12 ovary g/pellets per meal; 95% confidence interval (CI) between 5.29 and 16.81], although it has negligible effects on the date at which the maximum is reached and on the duration of the ovarian cycle. These findings evidence that ultrasonography can be used for an effective monitoring of ovary size dynamics in European seabass, providing real-time insights for broodstock management with minimal harming to fish. Precise estimates of the maximum ovary size, the date in which this maximum is reached and the ovarian cycle duration may help to identify the best candidate females for covering farm larval demand at any moment, thus enhancing welfare and broodstock management efficiency.