Effect of temperature on growth performance of greater amberjack (SERIOLA DUMERILI Risso 1810) Juveniles

In order to successfully diversify Mediterranean aquaculture, it is necessary to determine optimum culture conditions of potential candidate species such as greater amberjack (Seriola dumerili). Among culture conditions, rearing temperature is a key factor for achieving optimum growth and maintaining fish welfare. However, little is known about the optimum culture conditions of greater amberjack (Seriola dumerili). Thus, the aim of this study was to determine the effect of three different rearing temperatures (17, 22 and 26°C) during 120 days on growth performance, body morphometry, biochemical composition, gut transit and liver morphology of greater amberjack (Seriola dumerili) juveniles. After 120 days of rearing, fish raised at 26°C showed higher (p < .05) body weight and specific growth rate than fish held at lower temperatures, as well as improved feed utilization, protein efficiency and nutrient retention percentages. Fish stomach emptying was faster (p < .05) in fish raised at 26°C than in fish held at 22°C and 17°C. Similar results were obtained for gut transit time, being gut emptying faster (p < .05) in fish reared at 26°C than in fish cultured at lower temperatures. Rearing temperature also induced changes in fish morphology which resulted in a higher (p < .05) caudal propulsion efficiency index for fish reared at 26°C. Based on these results, we conclude that greater amberjack fingerlings perform better at 26°C than at 22°C or 17°C.     

Bottlenose dolphins share fish farm areas while maintaining sexual segregation: Investigating group memberships through spatially and temporally explicit parameters

1. Group membership is a key attribute of animal societies and central to the study of social structure in several taxa. However, social structure analyses are sensitive to the way data are collected and associations defined.
2. In this study, a time–space method was used to investigate the social structure of common bottlenose dolphins Tursiops truncatus observed and photographed across 7 years in the semi-enclosed Gulf of Corinth, Greece. Instead of adopting traditional group definitions, individuals were considered as being members of the same group if photographed within a specific time and space window. This approach can be applied post hoc across studies and can offer advantages under challenging sampling conditions (e.g. when dealing with groups spread over vast areas or when group membership is otherwise hard to assess).
3. Dolphins were mostly found around coastal cage aquaculture facilities farming European sea bass Dicentrarchus labrax and gilthead seabream Sparus aurata.
4. Dolphins formed clusters largely or entirely composed of individuals of the same sex, suggestive of sex-based homophily. Habitat partitioning was not detected: there was substantial spatial overlap among dolphin clusters, with all individuals using a relatively small area in the northern portion of the Gulf, where most of the productive fish farms were located. Associations between females were stronger than those between males, and daughters tended to stay in the group of their mothers.
5. Sex-based social clustering may allow females and calves to limit interactions with potentially aggressive males, while individuals of both sexes benefit from prey concentrated around fish farms.
6. Adaptation to foraging around farms can result in trade-offs between the costs and benefits of nourishment and social interaction. This may have both positive or negative effects on the animals that should be considered in the context of ensuring their favourable conservation status.