The effects of light and dark exposure on growth response of Clarias gariepinus fingerlings reared in glass aquaria

The study was carried out to determine the effect of light and dark exposures on the growth response of Clarias gariepinus fingerlings. A total of 120 four-week old Clarias gariepinus fingerlings (mean weight 0.52g~c0.02) were stocked into 20 litres of bore-hole water in glass aquarium (60x30x30) cm. Complete light, dark and normal photo periods were the experimental conditions evaluated. Growth indices such as mean weight gain and mean increase in standard lengths were significantly (p<0. 05) highest in the dark exposure with the following values respectively: (4.19 ~c 0.02g) and (4.11 ~c 0.19cm). Also, percentage survival (82.5%) in the dark exposure was higher than light and control (45% and 70% respectively). Light exposure had higher cannibalism rate (42.5%) than the dark and control (0% and 5 % respectively). Deep shiny black skin colouration was observed among the fingerlings in the dark exposure, while those in the light and control experimental conditions exhibited lighter and normal skin colourations respectively. The experimental conditions were not influenced by the water quality parameters (mean pH: 8~c 0.1 and temp: 28.1 ~c 0.60 ~'C) since their values were within the tolerable limit for fish culture throughout the 42 days experimental period.