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.     

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.     

Effects of background color on growth performances and physiological responses of scaled carp (Cyprinus carpio L.) reared in a closed circulated system

Growth performances and physiological responses of Cyprinus carpio after long-term (14 weeks) background color adaptation were investigated. Six groups of ten individuals each (initial body weight 116 g) were reared in black, green and white tanks (two replicate groups for each color). At the end of the experiment, blood (cortisol, glucose, haematocrit, cholesterol, triglycerides, total lipids, osmolality, electrolytes, pCO₂, pH), liver (total lipids, glycogen, hepatosomatic index) and growth (body weight, specific growth rate, food conversion ratio, condition factor, proximate carcass composition) parameters were determined. Plasma cortisol levels in white-adapted carp were significantly (P<0.05) lower than those in black, while in green-adapted fish did not differ significantly from those in both other counterparts. White-adapted carp showed the highest specific growth rate and the lowest food conversion ratio, whereas black-adapted fish exhibited the opposite pattern. In addition, mean (%) increase of body weight in white-adapted carp was 4.66 and 3.58% higher than that in black- and green-adapted fish, respectively. Furthermore in white-adapted carp, blood pCO₂ and pH were significantly higher and lower, respectively, than those obtained in black- and green-adapted fish. In black-adapted carp, liver total lipid levels were significantly lower, and plasma total lipid levels were significantly higher, than those in white- and green-adapted fish. No significant variations were observed in the other parameters. It is concluded that different background colors may lead to different growth performances of scaled carp depending upon rearing conditions.     

Mono- and duoculture of juvenile sharpsnout seabream Diplodus puntazzo (Cetti) and gilthead seabream Sparus aurata L. in a recirculated water system

Although the growth of intensively reared sharpsnout seabream Diplodus puntazzo (DP) has been suggested to improve in duoculture with gilthead seabream Sparus aurata (SA), the stocking ratio for most effective duoculture rearing has not been investigated. For this purpose, juvenile D. puntazzo (1.68±0.011 g) and S. aurata (1.43±0.007 g) were reared in duplicated groups of 165 specimens each, in two monoculture (100% DP, 100% SA) and four duoculture combinations (80% DP–20% SA, 60% DP–40% SA, 40% DP–60% SA, 20% DP–80% SA) for 96 days under recirculated water system conditions. Both species exhibited the highest growth when stocked at 20% and the poorest growth when stocked at 80%. For each species, no major differences for coefficient of weight variation and carcass proximate composition were detected. As the percentage of stocked S. aurata increased, D. puntazzo aggressiveness and weight variability of whole population were reduced, while total biomass, food consumption and food conversion ratio were increased. The results obtained are discussed in relation to fish behaviour and social interactions. From the fish farming point of view, it is indicated that under the present experimental conditions, juvenile S. aurata should be reared in monoculture and D. puntazzo in duoculture 40% DP–60% SA.     

Growth and physiological changes in scaled carp and blue tilapia under behavioral stress in mono- and polyculture rearing using a recirculated water system

Growth performance, carcass composition, liver and blood parameters ofscaled carp (C), Cyprinus carpio, and blue tilapia (T),Oreochromis aureus, reared for eight weeks in twomonoculture (100%C and 100%T) and two polyculture (60%C–40%T and40%C-60%T) conditions were investigated. In polyculture 40%C–60%T bothspecies achieved the highest levels of specific growth rate and the lowestlevels of food conversion ratio and carcass lipid content. In addition, theyexhibited the highest values of plasma pO₂ and pH and the lowestvalues of plasma pCO₂, cholesterol and albumin, although thedifferences among treatments were not significant in the case of tilapia.Tilapia showed significantly lower plasma Cl^– levels than underthe other conditions. Carp in monoculture and tilapia in polyculture60%C–40%T had the lowest levels of specific growth rate and significantlyhigher levels of liver lipids and plasma triglycerides than in the other groups.In addition, carp in monoculture exhibited a significantly higher haematocritthan in polyculture. No significant variations among treatments were observedconcerning plasma cortisol, glucose, osmolality, Na⁺, K⁺,HCO₃ ^– andHCO₃ ^–/H₂CO₃ in either species.The combination of scaled carp and blue tilapia, in which blue tilapia were themain species, proved to be the best for both species. It was suggested thatgrowth and physiological changes under mono- and polyculture rearing, in anintensive system, seem to be as a result of a different state of stress relatedto fish behavior.     

Common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>) response to two pieces of music (“Eine Kleine Nachtmusik” and “Romanza”) combined with light intensity,using recirculating water system

The objective of this study was to further investigate the effects of music on fish physiology, bearing in mind available information regarding the involvement of endogenous and exogenous factors in fish farming. Therefore, Cyprinus carpio (50.5 ± 0.36 g) were reared in a recirculating water system under 80 and 200 lux and subjected to no music at all (control, ambient noise only), 4 h of Mozart’s “Eine Kleine Nachtmusik”, or 4 h of anonymous “Romanza-Jeux Interdits” for 106 days. Both music treatments resulted in increased growth performance at both light intensities, with Romanza treatment at 200 lux resulting in better growth performance than Mozart treatment. Furthermore, feed efficiency for the Romanza groups was significantly better than for the control. Although no significant music effect was apparent for brain neurotransmitters, lower anterior intestine alkaline protease levels were detected for both music treatments. Taking into consideration the numerous advantages of recirculating water systems, it should be emphasised that fish response to music expresses the results of various physiological and biochemical processes, especially when fish notably respond differently when subjected to two different pieces of music.     

Combined effects of rearing density and tank colour on the growth and welfare of juvenile white sea bream Diplodus sargus L. in a recirculating water system

Appropriate rearing conditions for successful farming of white sea bream Diplodus sargus L. have not yet been studied in depth, while one of the major problems is the species increased aggressiveness. Given the known effect of density and background colour on fish growth, welfare and social behaviour, the present study aimed to investigate whether the two factors combined could favour D. sargus performance. Juveniles (17.37±0.06 g) were reared in white, light blue and black tanks under low (7 fish tank⁻¹ or 1.96 kg m⁻³) and high (28 fish tank⁻¹ or 7.79 kg m⁻³) density for 87 days. Water quality was not affected by experimental treatments. The best overall performance (growth, food utilization, body protein content, liver fatty acids) was achieved under low density and white or light blue tanks. Increased incidence of social interactions was indicated in fish under high density or when reared in light blue and black tanks. The present results clearly suggested that the use of black tanks should be avoided. On the other hand, stocking D. sargus at a density of up to 7.79 kg m⁻³ may be feasible because productivity was greater even if growth was slower. In this case, however, the use of white tanks is highly recommended.