Effects of air replenishers on the growth and body morphology of four fish species in an underwater aquaculture system

Abstract

The objective of this study was to investigate the effects of air replenishers on the growth, body composition, energy budget, and body morphology of four fish species through simulation within a fully submersible cage environment. The experimental species included Paralichthys olivaceous, which experiences swim bladder degeneration, and Lateolabrax japonicus, Oncorhynchus mykiss, and Cyprinus carpio, which are physoclistous, physostomous, and physostomous, respectively, with each species (N = 5) having an initial weight of 69.12 g, 73.10 g, 55.57 g, and 74.65 g, respectively. The four species were investigated in each trial designed with three different equipment for a 35-day period. The fish in the control group (Ctrl) were cultured in the tank with airstones, the mesh group (ME) used a mesh to keep the experimental fish from the water surface and airstones above the mesh, and the replenisher group (RM) had an air replenisher and airstones under the mesh. The results showed that there were no significant differences in the growth, body composition, energy budget, and body morphology of L. japonicus and P. olivaceus in different trials. For O. mykiss and C. carpio, compared to the Ctrl and RM groups, the specific growth ratio (reduced by 28.2% and 42.7%, respectively), protein content (reduced by 2.5% and 16.8%, respectively), and fat content (reduced by 14.2% and 27.2%, respectively) decreased. The proportion of feeding energy allocated to growth in the ME group also decreased, whereas that lost in respiration increased. An air replenisher can reduce the impact on the isolation of O. mykiss and C. carpio from the water's surface. Additionally, the streamlining of the body of O. mykiss in the ME group significantly decreased, whereas C. carpio in the ME group became more slender. This study implies that L. japonicus and P. olivaceus are not affected by isolation from the surface in a 1-month submergence culture, such as in a submersible cage, and the same effects on O. mykiss and C. carpio can be mitigated by air replenishment. Moreover, O. mykiss and C. carpio may adapt to negative buoyancy in submergence by changing body shape which generates more lift during swimming.