Effects of rearing density on growth, brain neurotransmitters and liver fatty acid composition of juvenile white sea bream Diplodus sargus L.

White sea bream Diplodus sargus L. is a fish species that develops dominance hierarchies and aggressive behaviour against its conspecifics. On the other hand, stocking density is known to affect social interactions, while an appropriate density for D. sargus efficient farming remains to be elucidated. For this purpose, juvenile D. sargus (14.3 g) were reared in 88.4 L tanks, for 10 weeks, under six rearing densities (10, 15, 20, 25, 30 and 35 fish tank -1). Water quality was not affected by rearing density. Best growth, in terms of final weight, specific growth rate, weight variation and food utilization, was achieved at 10 fish tank-1. At this treatment the lowest body water content, hepatosomatic and splenosomatic indices, higher body and liver lipid content were also observed. Brain neurotransmitter results indicated increased dopaminergic activity in populations held at higher rearing densities, while serotonergic activity was not affected. Moreover, no significant differences were detected for liver fatty acids. Results of the present study, compared with previously reported data, suggest that, within the range tested, the lowest realistic rearing density for juvenile white sea bream would be 10 fish tank-1. Higher rearing densities led to decreased growth, which seemed to be related to changes in intraspecific competition and social behaviour. © 2005 Blackwell Publishing Ltd

Effect of Mozart's music (Romanze-Andante of "Eine Kleine Nacht Musik", sol major, K525) stimulus on common carp (Cyprinus carpio L.) physiology under different light conditions

It is well known that music could have relaxing and antidepressant effects on humans, other mammals and birds. The present study aimed to evaluate music effects on common carp Cyprinus carpio growth and physiology, under different light conditions. Therefore, common carp (130.9 ± 0.67 g) was reared, in recirculating water system, under constant darkness (D) or normally illuminated conditions (L) for 12 weeks. Classical music was transmitted underwater and music treatments consisted of no music at all (control groups, C) and three music transmissions either of 30 min duration at 1.5 h intervals (M30) or of 60 min duration at 1 h intervals (M60). Obtained results showed that light conditions had a negative effect on fish growth (L-C versus D-C, P < 0.01), but when 30 min music was transmitted (L-M30) growth was improved and equal to D-C. Fish groups presenting reduced growth exhibited significantly increased brain neurotransmitters levels, indicating the occurrence of stressful conditions. Also, music transmission significantly affected carcass and liver fatty acid composition. Present results showed that music could be regarded as a stress relieving or inducing factor. Possible use of music as a growth and product quality promoter, as well as a means to ensure fish welfare under intensive fish farming is discussed. © 2006 Elsevier B.V. All rights reserved

Effects of light spectrum on growth and physiological status of gilthead seabream Sparus aurata and rainbow trout Oncorhynchus mykiss reared under recirculating system conditions

Previously reported data clearly indicate that depending on species, ambient light spectrum can affect fish growth, physiology, behaviour, reproduction, etc. Since light spectrum can be easily controlled in intensive indoor fish farming facilities, the present study aimed to investigate the effects of coloured light on growth performance (body weight, growth rate, food utilization, carcass composition, etc.) and physiological status (blood and plasma parameters, brain neurotransmitters, tissue fatty acid composition, etc.) of two widely reared fish species, gilthead seabream Sparus aurata and rainbow trout Oncorhynchus mykiss. For this purpose, 240 specimens of S. aurata (29.8 ± 0.13 g) and 60 specimens of O. mykiss (71.4 ± 0.30 g) were exposed to white (full-spectrum, fluorescent lamps), red (605 nm) and blue (480 nm) light (lamps covered with appropriate filters) for 11 weeks under recirculating water systems. Blue light had a significantly negative impact on O. mykiss growth performance accompanied with reduced liver total lipids and plasma glucose and increased brain serotonergic and dopaminergic activity. In the case of S. aurata, red light significantly increased brain dopaminergic activity, while a tendency towards reduced growth was also observed. Since these results indicated the establishment of stressful conditions, O. mykiss and S. aurata should not be reared under blue and red light, respectively. For each species, the effect of the remaining light colours tested, was not clearly differentiated so that an appropriate light spectrum for the most efficient farming of O. mykiss and S. aurata could not be suggested, at least for the time period examined. Nevertheless, present results suggest that light colour should be regarded as a rearing factor worth to be further investigated, especially when recirculating systems are concerned. © 2007 Elsevier B.V. All rights reserved