The effects of stocking density and social interaction on acute stressresponse in Nile tilapia Oreochromis niloticus (L.) fingerlings

摘要

Several researchers have demonstrated that the stocking density and socialinteractions between conspecific fish have significant influence on stressresponse. Nile tilapia Oreochromis niloticus (L.) is a teleost fish withhierarchical organization, Nile tilapia fingerlings (20 +/- 5 g) weredistributed in 30 tanks, 12 tanks with single fish and six with paired,groups of ave and 10 fish, respectively, and held in these 100-L plastictanks for 60 days. Six tanks of single fish and three of other groupsreceived an acute stressor on the 61st day. The control fish reared singlyand in pairs showed a plasma cortisol concentration similar to thatnormally found as a resting cortisol concentration in other fish. Onesurprising result was the absence of the formation of a hierarchicaldominant/submissive relation between the fish held in pairs. One possibleexplanation For this result is the volume of the tank, so that each fishexerted a territorial position in a corner of the tank. and the fightingand antagonistic encounters did not occur, In the five- and 10-fishgroups, the resting plasma cortisol concentrations were higher, which mayindicate a chronic stress response during the 60 days of the experiment,attributable to social stress, The application of an acute stressorsignificantly increased the plasma cortisol levels in all stockingdensities, with values reaching 135-298 ng mL(-1). When comparing thestressed fish, the 10-fish groups showed a more intense stress response inrelation to the other groups. [References: 23]