Evaluation of some biological parameters of Threadfin bream (Nemipterus japonicus) from the Persian Gulf (Bushehr province)

Japanese threadfin bream (Nemipterus japonicus) is one of the most important commercial species of fishes in the Persian Gulf. The purpose of this research was to elucidate some features of the sexual cycle and nutritional traits of fish caught in the Persian Gulf (Bushehr province) from September 2012 to September 2013. The total number of 315 fish was studied. The number of male and female fish was 101 and 184 respectively and the sex of 30 of them was not recognizable due to fish prematurity. Total length (TL) ranged from 20 to 36 cm with a mean (±SD) of 28.15±2.9 cm for females, whereas for males it ranged from 20.6 to 40 cm with a mean (±SD) of 31.48±4.1 cm. Moreover the minimum and maximum measured lengths were 20 cm (found in females) and 40 cm (found in males), respectively. The weight of female fish ranged from 98 to 303 g with a mean (±SD) of 172.06±3.8 g, whereas for males it ranged from 100 to 380 g with a mean (±SD) of 242.21±7.76 g. The average amounts of condition factor were 1.8±0.07 and 1.86±0.09 for males and females, respectively. The average amount of intestine relative length mean was 0.91 for all samples. Vacuity index was calculated in different months for evaluating the severity of feeding. The maximum and minimum amounts of filled stomachs were observed with 85% and 28.12% of filled stomachs in August and April, respectively. From 315 examined stomachs, 122 were empty and the others were full. The predominant food in the full stomachs was crab (56%) followed by fish (27%), shrimp (17 %), polycheat (8%), squid (4%), lobster (2%) and octopus (1%). The trend of GSI changes in females from February to April was upward and after that it became downward. Hepatosomatic index (HSI) fluctuations in males and females were similar to each other and conformed to GSI changes. The results showed that this fish was relatively gluttonous and crustacean was their main source of food, whereas fish and mollusks were their secondary source of food.