Effect of type of food and culture density on the rearing of Seriola dumerili

Dissertação de mestrado, Aquacultura e Pescas, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2013This thesis intended to study the effect of three different types of food and two different densities, on growth, survival, plasmatic parameters and lipid composition of muscle and liver of Seriola dumerili (Risso 1810) juveniles, in order to select an optimal feeding regime for growth, covering the nutritional requirements, and optimizing the commercial cost-effectiveness of the production. Regarding this, a total of 145 juvenile of Seriola dumerili with and average weight of 117.54 ± 54.98 g, were randomly distributed in 3 groups of 15 fish / tank (low stocking density LD) and 3 groups of 25 fish / tank (high stocking density HD) and fed with three different types of food: commercial pellets for Sparidae, the Alpha Biomar diet (SP), commercial pellets for S. dumerili (Skretting) (SE) and frozen Mackerel (MA). The study was conducted for 86 days. The study variables were the feeding regime and stocking density. The survival rates were higher in the groups fed with SE, while the Specific Growth Rate (SGR) showed no statistical differences (P>0.05) between groups. The groups fed with MA diet had the higher amounts of Daily Food Ingested (DFI), (9.59±3.56 g/fish at HD and 8.46±5.00 g/fish at LD) during the study, although with a higher Food Conversion Rate (FCR), (9.59 % at LD and 8.46 % at HD), not efficiently turn that ingestion in biomass, as for example the value of B% at groups fed with MA at LD (0.18 %) and at HD (-0.35%) show, being lower than the groups fed with SE at LD (0.41%). The biochemical composition of the fish in the present study was similar to the one reported in previous works, explaining that the more moisture content in the tissue, the less lipid it has in it. The Total Polar Lipids (TPL) and Total Neutral Lipids (TNL) did not show any significant differences (P0.05). Among the total neutral lipids (TNL), despite DAG, CHO and FFA were significantly different (P<0.05), TAG was the most abundant lipid class, which is generally the major lipid class in the diet of marine fish, and there was no significant differences (P<0.05) between the different groups. Regarding fatty acid composition, namely 18:1n-9, the groups fed with MA were the only significantly different (P<0.05), and the lowest amounts in this study (P<0.05), even taking in consideration that, in the wild, the S. dumerili diet is composed mainly by several finfish rich in 18:1n-9. We can deduce that or there was a degradation of the quality of the MA while stored to be fed to the groups, which affected directly the quality and quantity of the 18:1n-9. The fact that 18:2n-6 had its lower amounts in groups fed with MA, and the higher amounts in groups fed with SE (P<0.05), and taking in account that 18:2n-6 is the higher representative of n-6 fatty acid in diets, that is the fatty acid responsible for the most detrimental modifications to the fatty acid composition of cultured fish, suggest that this fatty acid is in excess in SE diet composition. The groups fed with MA presented the highest amounts of ARA (P<0.05) and the lower amounts of EPA (P<0.05), and the groups fed with SE presented the lower amounts of ARA and DHA (P<0.05). The lower amount of EPA and lower EPA/ARA ratio (P<0.05) found in groups fed with MA, could positively affect certain physiological functions. Due to the EPA and DHA competition for the same enzymes to esterify fatty acids into phospholipid structures, excessive accumulation of EPA could be prejudicial. In the groups fed with SE, the production of DHA was probably affected by it. The fact they had the lower amounts of ARA and DHA, inducing to a higher EPA/ARA ratio (P<0.05), suggests that the ratio is unbalanced and there is too much EPA accumulation, to insure ARA production Even though the group fed with MA at HD had the higher amount of DHA in this study (P<0.05), still the ratio DHA/ARA had no significant differences (P<0.05), indicating a stable balance between DHA and ARA amounts. This study suggests that the fatty acid profile of the different groups reflected the fatty acid composition of the diets, namely regarding 18:1n-9, 18:2n-6 and 20:5n-3, 20:4n-6 and 22:6n-3. that had effects in the ratios of DHA, EPA and ARA, affecting the balance between them, which had directly affected the growth. Regarding the plasma analysis, total protein was the only displaying statistical differences between diets and densities, and the fact that the groups fed with SE and MA diet, showed higher protein content, could be related to the fact those diets have higher protein levels (48g/l and 51.25 g/l respectively). From the present results it seems that the fatty acid composition of the pellets and frozen atlantic mackerel, affected the fatty lipid profile of S. dumerili, and so it development, so better balance between EFA diet composition while probably insure better energy efficiency and promoting growth. Considering the results obtained with SE, it seems to be the most appropriated for S. dumerili in the present study