Effects of flow rate on growth performance and welfare of juvenile turbot (Scophthalmus maximusL.) in recirculating aquaculture systems

Abstract

The effects of flow rate on growth and welfare of juvenile turbot (Scophthalmus maximus L.) were investigated in the present study. Fish with same initial weight (102.5 +/- 10.6g) were subjected to four flow rates, equalling to 0.5, 1, 1.5 and 2 tank volumes per hour in twelve 392L tanks during 80days. Results showed that specific growth rate of turbots increased (0.40-0.58%day(-1)) significantly with promoted flow rate (P<0.05). Total ammonia nitrogen, nitrite nitrogen, unionized ammonia nitrogen, chemical oxygen demand, total bacteria and total vibrio in tanks were affected significantly by flow rate and accumulations were found in low rate (200Lh(-1)) (P<0.05). Free carbon dioxide increased significantly with the increased flow rate and ranged between 4.5 and 13.5mgL(-1) (P<0.05). Both superoxide dismutase activity and lysozyme activity increased significantly with flow rate (P<0.05), with ranges of 108.51-131.57UmL(-1) and 551.81-869.28U mL(-1). Serum cortisol showed reversed tendency and ranged between 7.39-19.26ngmL(-1). The principal components analysis suggested that increased flow rate promoted fish welfare. It was concluded that increased flow rate promoted the growth of juvenile turbot, possibly explained by fish welfare differences in combination of health, water quality and serum parameters.