~ 279 ~ International Journal of Fisheries and Aquatic Studies 2016; 4(6): 279-283 ISSN: 2347-5129 (ICV-Poland) Impact Value: 5.62 (GIF) Impact Factor: 0.549 IJFAS 2016; 4(6): 279-283 © 2016 IJFAS www.fisheriesjournal.com Received: 10-09-2016 Accepted: 11-10-2016 Salum S Hamed (a) University of Dar es Salaam, Institute of Marine Sciences, Zanzibar, Tanzania (b) University of Dodoma, College of Natural and Mathematical Sciences, Department of Biotechnology and Bioinformatics, Dodoma, Tanzania Narriman S Jiddawi University of Dar es Salaam, Institute of Marine Sciences, Zanzibar, Tanzania Bwathondi POJ University of Dar es Salaam, College of Agricultural Sciences and Fisheries Technology (CoAF), Department of Aquatic Sciences and Fisheries, Dar es Salaam, Tanzania Correspondence Salum S Hamed (a) University of Dar es Salaam, Institute of Marine Sciences, Zanzibar, Tanzania (b) University of Dodoma, College of Natural and Mathematical Sciences, Department of Biotechnology and Bioinformatics, Dodoma, Tanzania Effect of salinity levels on growth, feed utilization, body composition and digestive enzymes activities of juvenile silver pompano Trachinotus blochii Salum S Hamed, Narriman S Jiddawi and Bwathondi POJ Abstract The present study was conducted to investigate the effects of different salinity levels on growth, feed utilization, body composition and digestive enzyme activity of silver pompano (Trachinotus blochii). Three treatment groups (designated as S1, S2 and S3) and a control group (S), each in triplicates, was established. The pompano in the control were kept at salinity of 34 ppt and those in S1, S2 and S3 were kept at salinity of 5, 15 and 25 ppt, respectively. After 56 days, growth performance was significantly higher (P<0.05) at S2 and S3 treatment. Body composition was significantly affected by salinity levels (P<0.05). The specific activities of amylase and total alkaline protease enzymes were significantly higher (P<0.05) for S2 and S3 respectively. The results collectively suggested that intermediate salinity of 15 ppt and 25 ppt improve the growth performance, feed utilization and digestive enzyme activity of pompano. Keywords: Salinity Growth Body composition Enzyme activity 1. Introduction Salinity is one among the environmental factors which are extensively affecting fish growth (Lisboa et al. 2015) [12] . Understanding of optimum salinity of specific species will contribute in expansion of aquaculture productions by utilizing wide range of culturing environments including the brackish waters). Inadequate rearing salinity levels for both freshwater and marine fish species directly affects fish physiology which results in the reduction of growth, survival, immune respond and disease resistance (Semra, 2013) [19] . Therefore, fish are constantly adjusting to their external surroundings environments and maintaining the proper balance of salt solutions within their bodies (isosmotic) by osmoregulation (Lisboa et al. 2015) [12] . Nevertheless, osmoregulation mechanism is energy demanding processes, species with lower metabolic rates utilizing about 20 to 50% of the total energy available (Ramos et al. 2010) [18] . In addition the effects of salinity in fish growth performance and survival rates are unlikely to be demonstrated by single factor rather than interaction of multiple factors including digestive enzymes activities. Foods particles are ingested with salt from surrounding environment alter the ionic concentration in the gastric lumen where enzymes are found. The salinity variation in the gastric lumen may alter digestive enzymes activities which affect feed digestibility and fish growth performance by increasing energy demand in continuous ionic regulation (Moutou et al. 2004, Tsuzuki et al. 2007, Gheisvandi et al. 2015, Vargas-Chacoff et al. 2015) [16, 20, 7, 21] . It is well known that fish digestive enzyme activities correlate with feeding ecology and diet requirement (Tsuzuki et al. 2007) [20] . Therefore, aim of the present study was to quantifying the extent of salinity effects on enzymatic activity and growth performance of silver pompano which will contribute in the improving its aquaculture production. 2. Material and Methods 2.1 Experiment set up Juveniles of T. blochii caught from the sea off Nungwi located at 5.7 0 S and 39.3 0 E of Zanzibar, Tanzania were used for the experiments. Experiments were conducted in triplicate in 1000 L tanks with 10 juveniles (average initial length: 5.52 ± 0.23 cm, average initial weight: 2.64 ± 0.31g) per tank. During this period of 28 days of acclimatization to different salinity