Influence of acclimation temperature on the osmotic regulation and survival of rainbow trout (Salmo gairdneri) rapidly transferred from fresh water to sea water

Certain physiological responses of two groups of rainbow trout acclimated at 10 and 17°C to a sudden change in salinity were investigated in order to determine the most appropriate temperature for direct transfer in salt water. Plasma osmolarities of fish acclimated at 17°C increased at a much faster rate following transfer and approached a much higher value than that reached by the fish acclimated at 10°C. The same was apparent for body tissue dehydration. Haematocrit values, the number of red blood cells, as well as red cell volume showed no significant difference between the two groups of fish for most of the experimental period. The larger increases in plasma osmotic pressure and tissue dehydration observed at 17°C are discussed in connection with the physiological adjustments accompanying higher temperature acclimation.     

Environmental conditions at sea-cages, and ectoparasites on farmed European sea-bass, Dicentrarchus labrax (L.), and gilt-head sea-bream, Sparus aurata L., at two farms in Greece

Water quality in sea-cages, and metazoan ectoparasites on bass, Dicentrarchus labrax (L.), and bream, Sparus aurata L., were sampled at two fish farms in south-west Greece over 2 years. The seabed and marine life around the cages of one farm was surveyed using scuba. The most frequent and abundant parasites were the monogeans Sparicotyle chrysophrii and Furnestinia echeneis on the gills of bream, and Diplectanum aequans on the gills of bass. The copepod Caligus minimus occasionally occurred in the buccal cavity of bass, but only in low numbers. Prevalence and abundance of parasites increased with bass size but F echeneis levels decreased with bream size. There were no other clear relationships between water quality, parasite levels and fish size. Ammonia varied seasonally with sea temperature, and with oxygen levels below 6 mg 1^-1 on many occasions, it is possible that fish suffered stress from a combination of high ammonia and low oxygen conditions. There was no accumulation of waste food or faeces below the cages at the one farm surveyed, but there were thousands of wild fish, including mullet (Mugilidae), Spicara sp. and Diplodus spp., present around the cages. Water quality may be improved by changes in farm management, such as reducing stocking densities below the present 16 kg nr^-3. Oxygen should be monitored at the cages on site daily. How comparable environmental conditions and impacts, and parasitization are at other bass and bream sea cage farms is unknown.     

Effect of incubation temperature on carbohydrate digestion in important teleosts for aquaculture

The activity and capacity (activity × tissue weight) of digestive carbohydrases (total carbohydrase, α‐glucosidase, α‐amylase) was examined in vitro under a range of (more realistic) incubation temperatures (5, 18 and 25°C) and pH (7.6) more likely to be encountered during rearing, along the digestive tract of important teleost species for aquaculture (Dicentrarchus labrax, Sparus aurata, Oreochromis aureus, Oncorhynchus mykiss and Salmo salar). Results indicate, among other things, an overestimation of digestive carbohydrase levels when performing assays at 37°C, a different effect of temperature on digestive enzyme performance along the digestive tract of examined species, and the increased importance of α‐glucosidase towards carbohydrate digestion. Implications regarding the capacity of each species for carbohydrate digestion in nature, as well as feed manufacturing, are discussed.     

Blue tilapia Oreochromis aureus (Steindachner) carcass composition and haematology in relation to the female parent size under recirculated water conditions

The relation between female parent size/age of Oreochromis aureus (Steindachner) and their offspring carcass composition and some haematological parameters was investigated. Blood parameters (glucose, triglycerides, albumin, cholesterol, total lipid, haematocrit, osmolarity), proximate carcass composition (crude protein, crude fat, moisture, ash), and total lipid content of liver were evaluated. No clear differences between populations could be reported regarding carcass composition. However, the offspring of the smallest/youngest female parent gave the highest crude protein and the lowest crude fat levels, while that of the largest/old female parent showed an opposite picture. Results obtained on blood parameters and liver lipid content were not clearly related to the female parent size/age, nor to the final body weight of the populations, despite the statistically significant (P < 0.05) differences observed for glucose, triglycerides and plasma and liver total lipids. It is concluded that more research is needed in order that a clear correlation between the female parent size/age and the investigated biochemical parameters of their progeny to be established.     

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.     

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 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.     

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.