El cultiu de la cabra de mar, Maja brachydactyla: aspectes zootècnics, bioquímics i nutricionals del desenvolupament larvari

Memoria de tesis doctoral presentada por Mireia Andrés Roig para optar al grado de Doctora por la Universitat de Barcelona (UB), realizada bajo la dirección de la Dra. Guiomar Rotllant del Institut de Recerca i Tecnologia Agroalimentàries (IRTA) y la Dra. Alicia Estévez GarcíaThe spider crab, Maja brachydactyla (Crustacea: Decapoda; Brachyura) has a high economic and ecological significance, supporting fisheries along the NE Atlantic coasts (Spain, Portugal, France, Ireland and UK). The high fishing pressure tolerated by populations of this crab, together with its growth and reproductive characteristics define the species as potentially interesting for aquaculture. The main objective of the present work was to set the bases for the profitable aquaculture of the spider crab, M. brachydactyla, through the study and optimization of its larval growth under intensive culturing conditions. The work focused on three perspectives of study: (1) description of the changes occurring along larval ontogeny or development, both at morphological and biochemical/ physiological level; (2) study of viability for the production of good quality larvae along the year; (3) experiments designed to optimize specific larval culturing conditions of M. brachydactyla, at both zootechnical and nutritional levels. The study of larval development of spider crab had confirmed the great potential of its intensive rearing. Larvae of M. brachydactyla reared in the laboratory were almost identical to those collected from plankton, showing that the intensive rearing protocol is not affecting larval morphology or development. A diet based on enriched Artemia (EA) allowed a continued lipid accumulation throughout larval development of spider crab. The detailed study of the patterns of change of biochemical components during ontogeny had confirmed that this lipid accumulation is accompanied by an increase of neutral lipid reserves, indicating a good nutritional condition of larvae. The study of the variation in the fatty acid composition along ontogeny had shown that EA fulfills the larval requirements in essential fatty acids. The beginning of the planktotrophic life implies a rapid increase in linoleic and linoleic acids, which might be explained as a summative effect of the diet, concomitant with an increase in the eicosapentanoic (EPA)/ docosahexopentanoic (DHA) acid ratio that suggests a retro-conversion from DHA to EPA. However, the results suggested that potential deficiencies of EA in certain essential amino acids (Thr and Arg) and phosporus might threaten the optimum larval and juvenile condition. The enzymatic activities described in larvae of M. brachydactyla confirmed their ability to digest protein, carbohydrates and lipids as soon as they hatch. Significant variations during ontogeny were found only in total activities likely as a consequence of digestive system development. Spider crab larval production is reliable along the year, both in quantitative and qualitative terms. However, the decrease in vitamin A and E as well as in Lys, Val, His and trace elements (Cu, Fe) of the newly hatched larvae at the end of the year might be indicative of a nutritional deficiency in broodstock diets. An initial stocking density around 50 larvae L-1, at a temperature of 18±1ºC, 36¿ salinity and natural photoperiod is recommended for the larval culture of M. brachydactyla. Under these conditions, optimal feeding was obtained using EA at a daily prey: larva ratio of 60 metanauplii larva-1. The study of the nutritional condition of larvae had shown that a delay of two days in the onset of exogenous feeding might be considered the maximum allowable time that does not have negative effects on growth, survival and spider crab larval quality. Finally, preliminary experiments of replacement of live prey by an artificial microbound diet (MBD) during larval development of M. brachydactyla had demonstrated that replacements up to 50% had no significant effects on growth and survival at any stage of development. Assimilation efficiency of nutrients seemed to be limited due to the poor digestibility of MBD protein and lipid, which lead to a reduction in growth in the total replacement treatment. Further research to optimize digestibility and nutritional value of the microdiet, and to establish larval nutritional requirements is a needPeer reviewe