Dietary selenium requirement of yellowtail kingfish (<i>Seriola lalandi</i>)

The dietary selenium (Se) requirement of yellowtail kingfish (Seriola lalandi) in normal and infected conditions was investigated. The fish were fed one of five experimental diets;a control un-supplemented diet (3.35 mg/kg Se) or diets supplemented with Se to provide 4.86, 5.38, 5.85 or 6.38 mg/kg Se. After feeding for 6 weeks, the fish were challenged by Vibrio anguillarum immersion and then observed for 4 weeks. Supplementation of Se had no effect on feed intake, feed conversion ratio and survival over 6 weeks of feeding;however, it significantly increased growth and Se content in muscle tissues. The optimal Se level for maximal growth of yellowtail kingfish estimated by second order regression was 5.56 mg/kg. Following the bacterial challenge, the immune-stimulating effects of Se were demonstrated in lysozyme and bactericidal activities, and there was a corresponding increase in survival and antibody response by supplementation of Se at ≥2 mg/kg (measured Se of ≥5.38 mg/kg). Under normal and infectious conditions, antioxidant capacity of fish measured as glutathione peroxidase activity increased by supplementation of Se. During post-challenge period, haematocrits were higher in the fish fed Se supplemented diets than the fish fed the control diet, while more macrophage aggregates were seen in the control group than in the others. Furthermore, there was evidence of myopathy in fish fed the diet without Se supplementation. Therefore, the results indicated that the optimal dietary Se requirement of yellowtail kingfish is 5.56 mg/kg.

Variation in the life-history traits of a Schilbid catfish,Clupisoma garua (Hamilton, 1822) in the coastal waters of southern Bangladesh

For the first time, the present study reports the life-history traits, comprising length-frequency distribution （LFD）, sex ratio （SR）, length-weight relationships （LWRs）, condition factors （CFs）, and relative growth （WR）, of Clupisoma garua in the coastal waters of Bangladesh. A total of 150 specimens ranging from 8.60 to 25.20 cm total length （TL） and 4.26 to 128.80 g body weight （BW） were collected using traditional fishing gear from August 2013 to July 2014. The overall sex ratio of males to females in the study did not differ significantly from the expected value of 1：1 （χ2=0.96, P〈0.05） but there were significant sex differences （P〈0.05） in the intercepts and slopes of graphs characterizing traits in C. garua. The calculated b values for the LWRs were 2.955, 2.893 and 2.927 for males, females and combined sexes, respectively, and there was negative allometric growth in all cases （b〈3）. The condition factors （KA, KF, KrR） and relative growth （WR） also did not differ significantly （P〈0.05） between the sexes. This study provides a useful tool for fishery specialists to evaluate the relative condition of fish and to initiate early management strategies and regulations for the sustainable management of the remaining stocks of this species in the entire coastal region of southern Bangladesh.