Effects of light intensity on growth of juvenile Brazilian flounder Paralichthys orbignyanus

Abstract

Most fishes require a minimum threshold light intensity to be able to develop and grow. The aim of this study was to evaluate the effect of light intensity on growth of juvenile Brazilian flounder Paralichthys orbignyanus. Juvenile flounder (1.55 ± 0.03 g) were randomly distributed into twelve 50 L tanks (75 fish per tank). Light intensities tested were 5 (5 ± 1 lux), 180 (176 ± 6 lux), 700 (712 ± 29 lux) and 2,000 lux (1,998 ± 64 lux), all in triplicate. Throughout 42 days, fish were fed a commercial feed until satiation. Salinity was maintained at 32 g L^-1, temperature at 23°C, dissolved oxygen at 6.6 mg L^-1, pH at 7.8 and un-ionized ammonia at 0.01 mg L^-1 NH₃ - N. At the end of the experiment, juveniles reared at 5 and 180 lux reached respectively 10.1 ± 0.3 and 9.44 ± 0.3 g, their weight was higher than those reared at 700 lux (8.45 ± 0.3 g) and 2,000 lux (8.44 ± 0.3 g) (P<0.05). Specific growth rate was higher at 5 lux (4.6 ± 0.2%), compared to that at 700 lux (4.0 ± 0.1%) and 2,000 lux (4.0 ± 0.1%) (P<0.05), while fish reared at 180 lux (4.3 ± 0.1%) did not differ from the other treatments (P>0.05). Survival was 100% at all light intensities tested. It was observed that juvenile Brazilian flounder growth is affected by light intensity, and, according to the results obtained, they should be reared at light intensities ranging between 5 and 180 lux.