Inês Martins

University of the Azores | UAc · Institute of Marine Research - IMAR

Swallowtail seaperch, Anthias anthias, is a popular fish in the public aquaria industry worldwide, but is subject to barotrauma and high mortality rates if an appropriate decompression profile is not used. Here, we analyze behavioral response to pressure reductions in swallowtail to define protocols for mitigating surfacing mortality. Four different pressure reduction rates were tested (15%, 25%, 35%, and 45%) in several lifting steps from an initial depth of 30 m. Decompression using this procedure was done with 12 and 24 h acclimation duration at each step allowing fish to recover from the pressure reduction. Fish condition was assessed based on swimming behavior, immediately after each new pressure reduction also after each acclimation time. Additionally, fish condition was monitored in a post-decompression trial for 14 days. During decompression, both conditions - initial and final - showed statistically significant differences in the reduction rates tested but showed no differences in acclimation times, and no interaction of the two factors. Neither pressure nor acclimation time affected the condition of the animal in post-decompression trials. Ascension steps near the surface are associated with larger decreases in neutrally buoyant fish compared to deeper decompression steps. Close monitoring of the effect of decompression on A. anthias in the control group, showed that a 29% reduction in pressure could indicate an approximate value of the free vertical range of this species, while swimbladder rupture can occur between 63 and 70% of pressure reduction. The optimal protocol for mitigating surfacing mortality combines two decompression profiles used in this experiment with a total duration of 84 h and comprising 4 lifting steps. The protocol developed to mitigate surfacing mortality was designed for conditions where oceanic cages or containers can be lifted gradually.