| Abstract |
At present, fish farming in the Mediterranean Sea is based almost exclusively on gilthead sea bream (Sparus aurata) and European sea bass (Dicentrarchus labrax). The need to diversify the number of reared fish species has been identified a method to ensure the sustained growth of the industry. Meagre (Argyrosomus regius) is one of the candidate species, since it exhibits a fast growth rate and is strongly appreciated for its flesh quality; and it has been ranked 7th among 27 candidate species for aquaculture development. Since scientific knowledge of the culture of meagre is scarce, the aim of the present study was to contribute some basic information on growth and culture of meagre. Stocking density is a major factor affecting fish growth under farmed conditions. The objective of the first experiment was to evaluate the effects of stockind density on growth, feed utilization, body composition and serum metabolites of meagre juveniles. Triplicate groups of fish (average weight ± SD, 84±10 g) were stocked in nine 500-L cylindrical tanks, under stocking densities of 12, 24 and 48 fish per tank (low, medium and high), for seven months. During the trial, fish were individually weighed every month. Two fish from each replicate at the end of the trial were randomly sampled and pooled for whole body composition analysis. Wet weight, viscera and liver weights were recorded for determination of hepatosomatic and visceral indices. Furthermore, liver and muscle samples were taken from three other fish per replicate for glycogen and lipid determinations. Serum metabolites were measured by enzymatic colorimetric methods using commercially available kits. All data are presented as mean ± SEM. During the experimental period, body weight and total length of fish held at medium stocking density were significantly higher than that of fish stocked at high and low density (ΑNOVA, DNMR, p<0,05). Despite these differences, the statistical analysis of the final data indicated no significant differences among the three stocking densities (length: 272,5±5,2 mm and weight: 214,7±11,6 g). Specific Growth Rate (SGR: 0,46±0,02), Feed Conversion Ratio (FCR: 1,26±0,10) and Condition Factor (CF: 1,05±0,01) were not affected by stocking density. There was no significant difference in hepatosomatic or viscerosomatic indexes. Proximate analysis indicated that the ash content of whole body was affected by stocking density, whereas the other chemical components of whole body and muscle were unaffected by the different levels of stocking density. Whole body of fish held at low stocking density showed significantly lower values (2.38 ± 0.23%) of ash content than fish stocked at medium (3.94 ± 0.17%) and high stocking density (3.31 ± 0.32%). Liver glycogen was not affected by stocking density, but there were significant differences in liver lipid content among the three stocking densities (high: 15.37 ± 0.68%, medium: 8.87 ± 0.58% and low: 19.18 ± 1.66%). Serum metabolites did not show significant differences among the three stocking densities. In conclusion, since stocking density did not affected growth performance of meagre, high stocking densities (22 kg m-3) can be applied to the culture of the species.
The objective of the second experiment was to evaluate the effects of dietary lipid levels on growth, feed utilization, body composition and serum metabolites of meagre juveniles. Triplicate groups of fish (average weight ± SD, 229.7 ± 1.4g) were fed three isonitrogenous (43% crude protein, Dry Matter) experimental diets containing 13, 17, or 21% lipid for 16 weeks. During the trial, fish were individually weighed every month. Twelve fish at the beginning and two fish from each replicate at the end of the trial were randomly sampled and pooled for whole body composition analysis. Wet weight, viscera and liver weights were recorded for determination of hepatosomatic and visceral indices. At the end of the trial, liver and muscle samples were taken from three other fish per replicate for glycogen and lipid determinations. Serum metabolites were measured by enzymatic colorimetric methods using commercially available kits. All data are presented as mean ± SEM. Body weight, total length and Specific Growth Rate of fish fed the 17% lipid diet (weight: 385.4±1.1g, length: 337.0±0.8mm, SGR: 0.46±0.00% day-1) were significantly higher than that of fish fed the 13% (weight: 357.1±5.1g, length: 328.9±1.0mm, SGR: 0.40±0.00 % day -1), and 21% lipid diets (weight: 371.0± 1.8g, length: 333.4±1.2mm, SGR: 0.43±0.00% day-1) (ΑNOVA, DNMR, p<0,05). Daily feed intake was not affected by the dietary lipid level, but there were significant differences in feed conversion ratio (FCR) (17%: 1.38±0.03, 21%: 1.47±0.02, 13%: 1.61±0.03) and protein efficiency ratio (PER) (17%: 1.68±0.04, 21%: 1.59±0.02, 13%: 1.44±0.02). There was no significant difference in condition factor, hepatosomatic or viscerosomatic indexes. Proximate analysis indicated that the lipid content of whole body and muscle was affected by the diets, whereas the other chemical components of whole body, muscle and liver were unaffected by the increase in dietary lipid content. Whole body and muscle of fish fed the 21% lipid diet showed significantly higher values (body: 7.41 ± 0.45% and muscle: 0.64 ± 0.13%) than fish fed 17 and 13% lipid (body: 5.92 ± 0.12%, muscle: 0.37 ± 0.08% and body: 5.76 ± 0.23%, muscle: 0.31 ± 0.02%, respectively). Serum metabolites did not show significant differences among the three dietary lipid levels. In conclusion, meagre is a fish with medium lipid requirement and excess dietary lipid level should be avoided, since the increase of dietary lipid level beyond 17% resulted in higher fat accretion and impaired growth performance.
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Βιολογικές βάσεις καλλιέργειας του κρανιού (Αrgyrosomus regius)
