Recirculating aquaculture systems (RAS) offer significant biosecurity and water parameter control for broodstock management, but also allow for the accumulation of metabolites released through the fish gills, urine, and feces in the tank water, due to low water renewal . In spawning tanks, a ccumulating cortisol and sex steroids during the reproductive season can lead to endocrine, behavioral or welfare disorders of fish. In the present study, the spawning kinetics and reproductive performance of gilthead seabream Sparus aurata , kept in a recirculating aquaculture system (RAS) with natural cycling temperature vs. a flow-through system with constant temperature are compared. At the same time, the concentrations of cortisol and sex steroids , in both fish plasma and tank water , in the two systems are also compared.
T wo du plicated gilthead seabream broodstocks were formed: one was exposed to a flow-thr ough system with constant well water temperatures (18-20°C, Flow-through ), and the other one was under a RAS system with cycling thermal regimes (15-23°C, RAS group) , both under simulated natural photoperiod. T heir spawning kinetics (relative fecundity and fertilization percentage), egg quality parameters (embryo survival, hatching and 5-day larval survival) and plasma and water cortisol and sex steroid levels were followed.
The reproductive season of both groups began in December, when mean daily relative fecundity of both groups exhibited its lowest values, compared to the following months . Mean daily relative fecundity ranged between 7,500 and 46,000 eggs Kg-1 female body weight (Figure 1A) and was similar between groups. Mean fertilization per centage was also similar between groups ranging between 80 and 94% (Figure 1B). Plasma and water cortisol and s ex steroid levels were analyzed .
The full results of the study will determine whether stress and reproductive hormones accumulate in the RAS systems, and examine their effect on reproductive function and egg production and quality.