Biotic and abiotic factors influencing initial swimbladder inflation of the blue-finned sea bream Acanthopagrus cuvieri (Sparidae), with particular reference to aquaculture in Kuwait

Abstract

Acanthopagrus cuvieri is a sparid fish local to Kuwait and the Arabian Gulf. It is highly valued fish with low landings from local waters and is of great inference for mariculture. Larval rearing and on—growing procedures have already been established by the Kuwait Institute for Scientific Research. The species is prone to non development of swimbladders, and this is a common problem world wide among sparids and some other species. This abnormality can have a strong economic impact on the development of the industry for luxury species. The swimbladder in A. cuvieri larvae originates as an outgrowth of the dorsal wall of the foregut on the second day after hatching at 25*C. It appears to become functional when the larvae are 4 or 5 days old. The pneumatic duct, gas gland, and rete mirabile have already been developed by that time. The pneumatic duct atrophies and becomes no longer patent on day 10-12, thus ending the outside communication via the oesophagus. The larvae clearly require access to atmospheric air to initially inflate their swimbladders. The data from the vertical migration, larval aggregation, buoyancy and length ¡weight studies support and give details on how the initial swimbladder inflation takes place. The effects of selected biotic and abiotic factors on the success of swimbladder inflation were tested. Temperature, light intensity, photoperiod, aeration rate, egg batch, and rotifer:larva ratio all showed a strong effect on initial swimbladder inflation. By contrast, salinity, water- exchange and type of rotifer used did not show any clear effect on initial swimbladder inflation, the optimum rearing conditions that appear to maximize the success of initial swimbladder inflation are; 25*C, 40 ppt, 1000 lux, 24- hr illumination, 50-70 ml/mln of aeration, 8-hr water-exchange at 250 ml/min flow, 100-200 rotifer: larva, L-type rotifer and early egg batch. Based upon the data generated in this work, the nine abiotic and biotic factors can be grouped into three major strategies, namely: reduction of water surface tension, enhancement of larval fitness, and management of the vertical aggregation of larvae. In combination, these factors contribute to successful initial swimbladder inflation and good survival of larvae. Overall, this work summarises the development of the swimbladder in A. cuvierl larvae and clearly indicate how this first inflation may be maximised through careful husbandry and understanding of the biological processes involved.