Abstract

In designing aquaculture systems to optimize fish health, growth, and reproduction, aquarists may be overlooking effects of chronic ambient noise exposure from circulation pumps. We examined primary, secondary, and tertiary stress responses to this stimulus in the lined seahorse, Hippocampus erectus, as a model ornamental fish species.

Thirty-two seahorses were weighed, measured, and then housed individually in either loud (123.92 ± 0.96 dB re: 1 μPa at mid-level, 143.77 ± 0.51 dB at bottom) or quiet (107.91 ± 0.91 dB at mid-level, 118.41 ± 0.51 dB at bottom) tanks for one month. One-hour weekly behavioral observations were scored and tested between treatments and over time in a repeated measures ANOVA. At the end of the one-month trial, animals were euthanized, weighed and measured again. Blood was collected and processed for leukocyte differential determination, PCV, blood glucose, and plasma cortisol (using enzyme immunoassay). Organs were weighed to obtain hepatosomatic and gonadosomatic indices. Measures were tested between treatments with either the t-test or the Mann-Whitney U-test.

Despite apparent resolution of cortisol among animals in loud tanks to control levels (7174 vs. 5430 pg/mL median concentration, p > 0.1), animals housed in loud tanks lost significantly more weight (-2.22 ± 0.30 vs. -1.44 ± 0.28 g, p = 0.03) and declined more precipitously in Fulton condition factor (-0.0449 ± 0.0092 vs. -0.0019 ± 0.0126, p = 0.01). Immunosuppression was also apparent among loud tank animals, as demonstrated by lymphocytopenia (59 vs. 71%, p = 0.03) and heterophilia (36 vs. 23%, p = 0.02) in the leukocyte differential. Other measures were unremarkable. Physiological results suggest that ambient noise represents a chronic, subtle stressor to seahorses. Seahorses are able to achieve allostasis, but at bioenergetic and immunological expenses.

Behaviorally, animals in loud tanks made more adjustments (69 ± 18 vs. 27 ± 7, p < 0.01) on holdfasts in the first week, but habituated thereafter. This was coupled with marginally less time spent holding on to holdfasts in the first week (59 ± 7% vs. 77 ± 6%, p < 0.1). By week 4, the pathological and concomitant distress behaviors of piping and clicking (respectively) developed among animals in loud tanks (piping: 106.9 ± 96.5 vs. 3.1 ± 1.1, p < 0.05; clicking: 6.2 ± 3.2 vs. 1.1 ± 0.4, p <0.025). Yawning reflects general inactivity and its increased occurrence among animals in quiet tanks (12.5 ± 1.2 vs. 7.8 ± 0.8, p < 0.01) is consistent with greater activity observed among animals in loud tanks. Other behavioral results were unremarkable.

The results we have demonstrated are of particular concern to aquaculturists, where fish growth, condition, and disease resistance are critical to success. In light of these results, aquarists and aquaculturists are advised to consider the acoustic environment of their aquaria, and to incorporate soundproofing modifications during design and set-up of facilities to avoid the debilitating consequences that chronic loud noise exposure can have on fish health, growth, and welfare.

Acknowledgements

Many thanks to A. Noxon (Acoustic Sciences Corporation) for soundproofing materials, design, and technical support; D. Petty, T. Crosby, and J. Holloway (University of Florida) for assistance with diagnostic necropsy and blood processing; K. Harr (University of Florida) for advising blood smear evaluation; T. Edwards (University of Florida) for advising EIA analysis; M. Helmholtz (Above the Reef), R. Stevens and crew, and the Twin Rivers Marina for donating seahorses; Sea Critters Inc. for donating live Artemia; The Pier Aquarium for donating hydrophones; and to F. Bastos, J. Bound, J. Liu, B. Macke, A. Maness, K. Nuessly, S. Osborn, Z. Punjani, J. Rosenbaum, B. Slossberg, D. Snipelisky, A. Weppelmann, and E. Wilson for their participation in animal husbandry and behavioral observations.

This project was funded by the Mazuri Fund of the American Association of Zoo Veterinarians and the D.M. Smith Fellowship granted by W.J. Lindberg. P. Anderson was supported by an Alumni Fellowship granted by The University of Florida and by the Morris Animal Foundation Fellowship Training Grant, awarded to D. Parkyn, W.J. Lindberg, and P. Anderson.

This is a project of The Florida Aquarium's Center for Conservation.