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. 2015 Feb 17:3:e756.
doi: 10.7717/peerj.756. eCollection 2015.

The effects of venting and decompression on Yellow Tang (Zebrasoma flavescens) in the marine ornamental aquarium fish trade

Affiliations

The effects of venting and decompression on Yellow Tang (Zebrasoma flavescens) in the marine ornamental aquarium fish trade

Emily S Munday et al. PeerJ. .

Abstract

Each year, over 45 countries export 30 million fish from coral reefs as part of the global marine ornamental aquarium trade. This catch volume is partly influenced by collection methods that cause mortality. Barotrauma in fish resulting from forced ascent from depth can contribute to post-collection mortality. However, implementing decompression stops during ascent can prevent barotrauma. Conversely, venting (puncturing the swim bladder to release expanded internal gas) following ascent can mitigate some signs of barotrauma like positive buoyancy. Here, we evaluate how decompression and venting affect stress and mortality in the Yellow Tang (Zebrasoma flavescens). We examined the effects of three ascent treatments, each with decompression stops of varying frequency and duration, coupled with or without venting, on sublethal effects and mortality using histology and serum cortisol measurements. In fish subjected to ascent without decompression stops or venting, a mean post-collection mortality of 6.2% occurred within 24 h of capture. Common collection methods in the fishery, ascent without decompression stops coupled with venting, or one long decompression stop coupled with venting, resulted in no mortality. Histopathologic examination of heart, liver, head kidney, and swim bladder tissues in fish 0d and 21d post-collection revealed no significant barotrauma- or venting-related lesions in any treatment group. Ascent without decompression stops resulted in significantly higher serum cortisol than ascent with many stops, while venting alone did not affect cortisol. Future work should examine links in the supply chain following collection to determine if further handling and transport stressors affect survivorship and sublethal effects.

Keywords: Aquarium fish; Aquarium trade; Fish barotrauma; Fish cortisol; Fish physiology; Venting.

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Conflict of interest statement

Tim Miller-Morgan is an employee of Hatfield Marine Science Center.

Figures

Figure 1
Figure 1. Experimental design of ascent and venting treatments.
(A) Illustrates decompression stops for each ascent treatment. The rate of ascent between stops was 0.25 m/s for all treatments. Fish subjected to ascent without decompression stops were brought directly to the surface. Fish subjected to ascent with one decompression stop were brought to half the maximum depth for a 45 min decompression stop, then brought to the surface. Fish subjected to multiple decompression stops were brought up 3 m every 15 min. At 10 m (2 atm), these fish were brought up 1.5 m every 15 min. (B) Venting treatment scheme and fish sampling design. This experiment was replicated 3 times for a total sample size of n = 360 fish.
Figure 2
Figure 2. Barotrauma signs observed in Yellow Tang following collection.
(A) Positive buoyancy before venting and neutral to negative buoyancy following venting (B) intestinal protrusion from the cloaca and (C) exophthalmia.
Figure 3
Figure 3. Histologic views of swim bladder tissues in vented Yellow Tang.
(A)–(B) Representative histologic views of normal Yellow Tang swim bladder tissues in vented fish at (A) 0 days and (B) 21 days. Note lack of any inflammation, edema, or necrosis in lateral body wall (bw), coelomic cavity (c) swim bladder (sb), and rete mirable (rm). (C) Histologic section of needle track in a Yellow Tang subjected to venting showing muscle cell necrosis, edema, and neutrophilic inflammation: (1) Needle track, (2) needle entry through coelomic cavity, (3) neutrophilic inflammatory response.
Figure 4
Figure 4. Cortisol concentration (mean ± SE) by each treatment.
(A) venting and ascent treatments; (B) ascent treatments; and (C) venting treatments. Letter groups represent Tukey’s multiple range test results comparing means. All treatment groups were significantly elevated above the ocean baseline concentration of 8.9 ng/ml.

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Grants and funding

This research was supported by the National Oceanic and Atmospheric Administration Coral Reef Conservation Program [NA11NOS4820013] and Washington State University Vancouver. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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