Morphoanatomy of Pangasionodon hypopthalmus Reared Under Controlled Photoperiod

Abstract

Abstract Fish morphoanatomy is affected by environmental condition such as photoperiod duration. A research on the effects of shortened photoperiod on the morphoanatomy of Pangasionodon hypopthalmus has been conducted. There were 3 treatments applied, namely, 24 hours dark (24D), 18 hours dark (18D) and natural photoperiod (control). The fish, 8 cm total length (TL) and 4 gr body weight (BW) were reared in circular plastic tanks filled with 100 L freshwater and completed with aerators and circulation pumps, 30 fishes/tank. The fish was reared for 8 weeks and fed with commercial fish feed pellets, twice/day, at satiation. The dark condition was created by placing the tanks under dark tarp tents. Morphoanatomy data were studied by the end of experiment. Results shown that the survival of fish was 100%. The growth of fish reared in 24D and 18D was better, more than 20 cm TL and 85 gr BW, while that of the control was 18 cm TL and 72 gr BW. The condition factor as well as the liver condition of fish in all treatment was not different, it was around 1.2. The liver was reddish brown color, smooth and oily in which hepatosomatic index (HSI) value 0.023 in 24D; 0.027 in 18D and 0.048 in control. The visceralsonatic index (VSI) was 0.090 in 24D; 0.70 in 18D and 0.161 in control. In most of fishes reared in 24D and 18D, the gonad were in the 1st maturity stage (gonadosomatic index; GSI 0.0058 to 0.0068), while the gonad of some control fishes were in the 2nd maturity stage (GSI 0.0080). Data obtained shown that the morphoanatomical data (HSI, VSI and GSI) of the fish reared in lengthened dark were lower, but the growth data (TL and BW) was higher than those of the control, indicated that the fish reared in dark condition may allocated more energy for growing.