فهرست مطالب b. doust shenas

A 56-day research was carried out to determine the interactive effects of water temperature (WT) and salinity (WS) on physiological responses of yellowfin seabream, Acanthopagrus arabicus (Iwatsuki, 2013) (10.0±0.2 g). Three salinities (S; 12, 35 and 50 ‰) and four temperatures (T; 16, 23, 30 and 35°C) were selected to design 12 experimental treatments. The husbandry system consisted of thirty-six 300-L cylindrical polyethylene tanks that were filled with 250 L of water. Each treatment had three replicates (tanks) containing 20 fish in each tank. Fish were handfed on a commercial feed (440 g kg-1 crude protein and 180 g kg-1 crude fat) twice daily at visual satiation. Five fish from each tank were transferred into an experimental chamber to evaluate their oxygen consumption and ammonia excretion. There was a positive correlation between fish oxygen consumption and WT (r=0.594; p=0.001). In addition, there was a negative relationship between WS and ammonia excretion (AE) (r = -0.865; p=0.029), meanwhile the relationship between WT and AE was positive (r=0.422; P=0.01). Growth parameters were significantly affected by WT, WS and their interactions so that the highest final body was recorded in the highest temperature and salinity treatment. On the other hand, the lowest body weight was observed in the lowest WT (i.e., 16℃) irresponsive to WS. The moisture level in the whole body was affected by WT (p=0.012). The crude lipid in the whole body was influenced by only WS (p=0.04). The ash content in the whole body was profoundly affected by WT (p=0.0001), WS (p=0.0001) and their interaction effect (p=0.04). The energy content of the whole body was only affected by WT (p=0.025). The energy budget of fish was influenced by WT (p=0.0001) and its interaction with WS (p=0.015). In summary, the present findings indicated that the preferred WT for A. arabicus is between 30 to 35°C in brackish water.

The study investigated the stomach contents of Indian mackerel (Rastrelliger kanagurta) from the southern part of Qeshm Island in the Persian Gulf from April 2016 through March 2017. The food and feeding behavior of R. kanagurta with a fork length of 17.8 to 22.5 cm was assessed from the analysis of gut contents. The frequency of occurrence and numeric methods were used for stomach content analysis. R. kanagurta fed on diatoms, dinoflagellates, crustaceans, molluscs, forams and ciliates. Organisms of plant origin including diatoms (Bacillariophyceae) and dinoflagellates (Dinophyceae) were the main prey constituting about 72% of food items by number and 66.67% by the occurrence. Coscinodiscus sp. were found to be the most preferable food of plant origin constituting 46.92% by number and 12.88% by occurrence, followed by Guinardia sp. which constituted 9.74% and 7.58% by number and occurrence, respectively. Among zooplankton, crustaceans were the dominant prey contributing to 19.58% of the food items by number and 24.61% by occurrence. Copepoda was the most preferable crustacean constituting 7.57% by occurrence and 5.72% by number. Gastro-Somatic Index (GaSI) was found to be the highest in autumn and the least in winter that is before and after the spawning season. The stomach emptiness index was 36.15% indicating the comparatively gluttonous behavior of the fish. Overall R. kanagurta in the southern part of Qeshm Island in the Persian Gulf is planktonivorous and feeds on a wide range of planktonic organisms.