In aquaculture, fishes are often exposed to stress conditions, due to practices such as manipulation, grading, high stocking densities, transport, pre-slaughter conditions and slaughter methods. In order to reduce these stressors and to increase both fish welfare and production needs, it is seeking to introduce organic agriculture principles to the conventional aquaculture. Organic aquaculture is still relatively new in concept and development all over the World. The aim of the study was to investigate differences in fish welfare between two rearing systems: the conventional and the organic ones. Juvenile sea bass (Dicentrarchus labrax) were reared in two separated outdoor ponds and bimonthly monitored from May 2009 to November 2010. Organic vs conventional farmed fish welfare was evaluated through various stress and immunological parameters, besides growing performances. Particularly, stress response was evaluated through the analysis of serum cortisol and oxidative stress was investigated with an histochemical (melanomacrophage centres count and relative pigments content) and an immunohistochemical approach, using an antibody anti-4-hydroxy-2(E)-nonenal (HNE; a lipid peroxidation marker), besides glutathione analysis. Hematological and innate immunity parameter analyses were also carried out, such as hematocrit, leucocrit and serum lysozyme activity. At the beginning of the trial, the main difference between the two rearing systems was in the diet. The analysis of growth performance has shown a good level of growth, highlighting higher weight in animals reared under conventional aquaculture respect to those organic, difference that was significant only in the last sampling of November 2010 (p<0.05). Similar results were found from the analysis of the condition factor (K). Serum cortisol showed a significant difference only in two samplings (May 2009 and July 2010, p <0.05). Hematocrit showed significant differences especially in the samples after winter starvation, with higher value in conventional samples compared to those organic (p<0.05). Serum lysozyme activity showed no significant differences between the two rearing systems, except in May and July 2010 (p<0.05). Immunohistochemical analysis using an antibody anti-HNE showed an immunopositive staining in tissues such as spleen, kidney and liver, especially at the MMCs level. The MMCs count showed a higher number in organic animals if compared to the conventional farmed ones in all samples, except in March, May and September 2010. To deeply investigate these differences, the presence of different pigments within the MMCs has been analyzed, and did not showed any difference between the two groups. The analysis of glutathione (GSH) showed no significant differences between the two methods of farming with the exception of July and November 2010 samples (p<0.05). This is the first monitoring study on organic aquaculture on sea bass reared in pond in Italy. Concerning differences between rearing systems, this study highlighted a different growing trend, in which conventional farmed fishes were longer and heavier than organic ones. Concerning fish welfare, no significant differences were observed between the two rearing systems. But, since this was a monitoring study on a commercial farming, potential differences in the investigated parameters may have been mitigated, as the two systems didn’t differed so pronounced. On the other hand, main differences between the two rearing systems were found mostly in last samplings, particularly in November 2010. This could be interesting considering that at that moment fish reached the commercial size and were ready to be sold. Moreover, this suggests that in a research approach differences between farming conditions should be emphasized, in order to reduce time-depending changes and to highlight the main responsible that affect fish welfare.
File in questo prodotto:
Non ci sono file associati a questo prodotto.