عنوان مقاله [English]
To examine the combined effects of photoperiod and feeding regime on the growth and off-season parr-smolt transformation of juvenile Caspian brown trout (Salmo trutta caspius), fish of 5.85±0.13g were reared under four different photoperiods (Light: Dark, L:D) cycles (24L:0D, 16L:8D, 12L:12D, 8L:16D) and were fed with two foods (French and Iranian) which were broadly similar in composition, for 110 days. A CRD design in factorial method including the four photoperiod regimes and two foods, with three repeats and ten fish was used in this experiment. Results showed that fish which fed by both French and Iranian foods grew best and reached to smolt stage faster in (16L:8D) photoperiod. Although, the higher weight (11.03±0.06g) and length (4.64±0.28 cm) gain were observed in fish which fed by French food, but they did not significantly differ from the fish which fed by Iranian food (P>0.05). Condition factor (CF) was lower in the 16L:8D photoperiod than other treatments in both groups of fish without significant difference (0.84±0.06, 0.89±0.01%). Also, the lower feed conversion rates (FCR) was measured in (16L:8D) in French food which was significantly different from Iranian food. The higher amount of growth hormone was recorded at 17 January and the Na+, K+-ATPase activity was higher at 20 April without significant differences between two groups of fish. Also, the higher amount of growth hormone and ATPase activity were recorded in (16L:8D) without significant differences between two groups of fish. Our finding indicated that both French and Iranian foods can be recommended in the production of off-season Caspian brown trout smolts in the (16L:8D) photoperiod.