A study on the relationship between different fish loading densities and welfare in Rainbow trout (Oncorhynchus mykiss)broodstocks

In this study, it was investigated relationship between different stocking densities and wefare in rainbow trout (Oncorhynchus mykiss) brodstocks within scope of low (LSD) and high stocking density (HSD) according to water quality, physiological blood parameters, behavior and reproductive parameters. Study was conducted for six months through four months before spawning in August and two months after spawning in February. Fish stocking density was selected LSD 4 kg/m3 (0,12 kg L-1 min-1) and HSD 8 kg/m3 (0,24 kg L-1 min-1). Fish welfare assessed by measuring water quality (calcium (Ca++) and magnessium (Mg++) hardness, ammonia (NH3-N), nitrite (NO2-N) and nitrate (NO3-N)); physiological indicators (plasma cortisol, plasma estradiol, plasma total testosterone, lysozyme activity, erythrocyte and leucocyte number, haematocrit); behavioral response (position in water column, aggression, appettite); reproductive efficiency parameters (number and rate of spawners, absolute and relative fecundity, egg diameter, fertilization, eyed, hatching and fry-up rate, sperm motility, spermatocrit and sperm concentration); also survival rate of broods and compared statistically (p=0,05) There was no differences between LSD and HSD group in water quality parameters. All analysed water quality parameters was in the range of water quality parameters that indicated for rainbow trout culture in the literature. Although differences was found in plasma cortisol, estradiol and total testosteron concentration in certain months (p<0,05), there was no difference in lysozyme activity, erythrocyte and leucocyte number, haematocrit in physiological blood parameters except in a few months (p>0,05). Behavioral response was different, at especially position within water column, agression and appetite in certain months (p<0,05). Moreover reproductive efficiency parameters showed differences in number and rates of spawners, egg diameter, fertilization, eyed, hatching and fry-up rate, sperm motility (p<0,05). Survival rate of broods, total and relative fecundity, spermatocrit and sperm concentration didn?t show any differencies (p>0,05). In this study, according to results of analysis, HSD groups affected cortisol concentration that is basic stress factor and caused stress and negative effects on behavioral and reproductive parameters. As a result we suggest that rainbow trout broodstock should be stocked low stocking densities about 4 kg/m3 within the scope of fish welfare.When viewed from welfare aspect to legislation in Republic of Turkey, although fish and animal welfare have been used in regulations, it hasn?t been found any criteria for application of welfare in the field. We recommend that a contemporary regulation that applicable and traceable by farmers and authorized person should be prepared.