Trophic level, food preference and feeding ecology of Rachycentron canadum (Linnaeus, 1766), in Hormuzgan Province waters (northern Persian Gulf and Oman Sea)

This study examined the ecological factors associated with feeding in Rachycentron canadum (cobia) in the waters of Persian Gulf and Oman Sea. Seasonally variation of stomach condition of cobia male, females, pooled and size wise were analyzed. In general, 577 cobia were collected (340 males, 237 females) (20–161 cm Total length) from Sept. 2014 to Sept. 2015 by the Ferdows-1 survey ship and from the landing areas in Bandar Abbas harbor seasonally. Our results provide the first estimates of trophic level (Tr.L) (4.32±0.76, mean±Se), consumption per biomass (Q/B) (6.13), and aspect ratio of the caudal fin (ARc.f) (3.1) for R. canadum in the Hormuzgan Province. We also found that bony fish made up more than 80 percent of the relative importance of particular prey (IRI %), indicating R. canadum primarily preys on these species. The immature group (20–40 cm, T.L), tended to feed on Penaeidae family, small crabs, and mollusks. Hierarchical clustering revealed that the frequencies of different types of prey could be applied to categorize the length classes into three levels. The result of this study revealed that the immature group and the 20-40 cm length class tended to feed on Penaeidae family, crabs, and mollusks. Also, we found that males generally fed more than females in all seasons and that R. canadum had an average dietary intake. The findings of this study can be used to prepare a food formulation for cobia that resembles the native diet

Determination of median lethal concentration lead (II) nitrate and behavioral responses of hermit crab, Diogenes avarus

The LC50-96h test paradigm is used to measure the susceptibility and survival potential of organisms exposed to particular toxic substances, such as heavy metals. In this study, the statically acute toxicity of Pb on hermit crab D. avarus was determined according to standard methods O.E.C.D in 96h. 84 individual hermit crab with 0.19±.0.01 g weight average were used in five different treatments (75, 100, 150, 175, 200 microgram per liter of lead) with three replicates and a control treatment (15 hermit crab per in each treatment). The effective physical and chemical parameters of water including pH, total hardness, dissolved oxygen and temperature were controlled throughout the experiment. Finelly, the rate of the acute toxicity (LC50 96h) was determined to be 184.045 µg/l by using the statistic method Probity analysis. Furthermore, the rates of LC10, LC50, LC90 (24, 48, 72 and 96h) were calculated. Results indicate that when the experiment time is extended, lower concentration of Pb is leading to mortality in hermit crab D. avarus. The percentage of mortality increased with increasing duration of exposure of crab to different amounts of lead concentration. The behavioral changes observed in hermit crabs D. avarus in the experiment period included an imbalance in walking, reduced activity and movement, slow motion, no irritability and also color change of the abdomen