Effects of stocking density on growth and skin color of juvenile darkbarbel catfish Pelteobagrus vachelli (Richardson)

Abstract

A 3-month experiment was conducted to investigate the effects of stocking density on growth performance and skin color of juvenile darkbarbel catfish. Experimental fish (5.0 +/- 0.6 g; n = 160) were stocked in triplicate in 2 m(2) concrete tanks in a greenhouse at the initial density of 50, 150, 400 and 650 fish m(-2), respectively (0.42, 1.25, 3.33 and 5.42 kg m(-3)). At the end of the experiment, 60 fish from each tank were sampled to record body weight and total length, and six fish from each tank were sampled to measure skin color by instrumental color analysis. Results showed that stocking density affected growth performance significantly (P < 0.05). Final mean weight (W), final mean total length (L) and specific growth rate (SGR) were significantly higher at 150 fish m(-2) treatment and lower in both the highest and lowest (650 and 50 fish m(-2)) density treatments (P < 0.05). The condition factor (CF) was higher in 150 and 50 fish m(-2) and lowest at 650 fish m(-2) treatment; the coefficient of variation of weight (CV) tended to increase with the increase in stocking density, which was lowest in 50 fish m(-2) and highest in 650 fish m(-2). Stocking density also affected the skin color parameters, L* (lightness), a* (redness), b* (yellowness) and h* (hue), significantly (P < 0.05). The values of these parameters tended to decline with the increase in stocking density. Results of the present study suggest that growth performance and skin color responses to stock density exhibit different patterns for darkbarbel catfish juveniles: highest and lowest densities impaired growth rate, and higher density had a darkening effect on skin color.