Investigations on the use of the brown alga, 'Padina pavonica', (Linnaeus, 1758) in the farming of Gilthead sea bream, 'Sparus aurata, Linnaeus', 1758

Abstract

Aquaculture is an important agro-food production activity that provides valuable protein as well as necessary fatty acids (FAs) such as eicosapentanoic acid (EPA) and docosahexanoic acid (DHA) that have been recently being classified as very important in the nutrition of fish but also for human nutrition (FAO., 2008b). In the Mediterranean sea, just two marine species, sea bass, Dicentrarchus labrax, Linnaeus 1758 and gilthead sea bream, Sparus aurata, Linnaeus 1758, represent about 90% of the marine aquaculture production and despite the fact that significant efforts have been invested on diversifying production with new species, difficulties still exist in the commercialization of new species. Indeed, there is still need to improve current culture practices of these two species already established in aquaculture in order to improve broodstock quality, larval rearing and culture protocols, fish larval and growout practices and thus improve the quality of the final product. This will in turn contribute to overcoming the bottlenecks in the development of new protocols for the culture of new species for the. market. This research work is focused on the evaluation of the effects of Padina pavonica, (Linnaeus 1758) extract (henceforth referred to as PE) as a nutritional supplement in the diet of gilthead sea bream. Padina pavonica is a brown alga that grows in temperate regions in sea water. P. pavonica grows in large quantities in the Mediterranean Sea and in Malta there is an annual harvest of around 40 tonnes for the purpose of extracting PE. The alga, once harvested, is then processed to extract the active ingredient "Maltanedienol" (so named because it was first developed in Malta), which offers great potential for treating osteoporosis and arthritis sufferers. Maltanedienol is the principal component of PE. The investigations of its effects are not limited to human medicine but have now been extended to various fields such as agriculture while in other fields such as aquaculture it is under preliminary investigation and various pilot projects are under way. Production of rotifers Brachionus plicatilis, (Mueller 1786), with and without the use of PE was investigated in batch culture and continuous culture methods. Rotifers are essential in aquaculture, as this zooplankton is the primary first feeding prey in Mediterranean marine aquaculture. Results obtained in this study show that rotifer production using PE supplementation gave on a mean 25% higher production of rotifers than the control in batch culture 3 method. There was a significant difference in production between experimental and control tanks (p <0.001 ). In continuous culture of rotifers, even though there was no significant difference in the lifetime of the cultures of the two treatments, (p=0.13), there is a clear trend that lifespan of cultures using PE are longer than without PE. The mean fecundity of rotifers with supplemental PE in diets was 59 eggs/ml while cultures of the control had a mean fecundity of 41 eggs/ml. The mean fecundity between the two groups was statistically different (p=0.023). Larval rearing and grow out of gilthead sea bream has shown statistically significant differences in growth and time to reach market size. Larvae were fed with live and inert diets supplemented with and without PE. Also during growout, fish were fed with diets supplemented with and without PE. Mean weight of larvae on day 78 were significantly different between the groups (p=0.036) with Group (A) fed on diets supplemented with PE being higher than the group being partially supplemented (B) and the Control (C). Mean weight was 0.065g, 0.054g and 0.052g for groups A, Band C respectively. The combined net effect of PE supplementation of diets for rotifer production and the differences in the results obtained have a very significant impact on live food production and thus a significant economic impact on hatchery production of fingerlings. Mean weight of fish at the end of the experiment (market size) was significantly different with the fish fed on PE supplemented diets having 15% higher growth rate than the control diets. There was a significantly higher growth rate for the treatments fed on PE diets throughout the experiment. The treatment that never received supplementation with PE in its diet performed the worst. The mean fattening period to market size of 350 grams of weight was reduced by as much as 20% for the fish that were fed on diets supplemented with PE. Feed Conversion Ratio (FCR) at the end of the experiment was significantly different with the treatment that was fed on PE supplementation throughout the culture period having a lower FCR. Fatty acid profile of the market size fish revealed that there were significantly higher levels of unsaturated FAs and particularly of EPA and DHA in fish that received diets supplemented with PE. This study has clearly shown that PE which contains Maltanedienol and other active ingredients, even if in minute levels, could play an important role in larval development and growth and that these improvements can also provide for a better well-being and welfare of aquatic cultured animals in general. These attributes are bound to have significant positive effects on diversifying aquaculture in the Mediterranean Sea as these culture practices may be used on new species that could be possible candidates for aquaculture.