Sound, stress, and seahorses: The consequences of a noisy environment to animal health

Abstract We examined stress responses to chronic noise exposure in a popular aquarium fish, the lined seahorse (Hippocampus erectus). Thirty-two animals were housed individually in either loud (123.3 ± 1.0 dB re: 1 μPa total RMS power at mid-water, 137.3 ± 0.7 dB at bottom) or quiet (110.6 ± 0.58 dB at mid-water, and 119.8 ± 0.4 dB at bottom) tanks for one month. Weekly behavioral observations were scored and compared between treatment means, as well as treatment variances, because stressed populations often exhibit increased variance in measures. At the end of each trial, animals were euthanized, assessed, and means and variances of the following measures were compared between treatments: weight change (ΔWt), change in Fulton condition factor (ΔK), hepatosomatic index, gonadosomatic index, leukocyte count and differential, packed cell volume, heterophil to lymphocyte (H:L) ratio, blood glucose concentration, plasma cortisol concentration, parasite presence/absence and number of organs infected, and presence/absence of bacterial infection. Among behavioral results, tail adjustments and reduced or variable percentage of time spent stationary were interpreted as irritation behaviors. Animals in loud tanks were more variable in the number of tail adjustments made; this difference was especially significant in week one, when loud tank animals also made significantly more adjustments. Animals in loud tanks also demonstrated greater variation in the percentage of time spent stationary in the first week. Variability in these measures subsided after the first week, presumably due to habituation. Piping and clicking were considered pathological and distress behaviors (respectively). Animals piped and clicked more variably in loud tanks; this variability was especially pronounced in week 4. Other behaviors were unremarkable. Among physiological results, animals in loud tanks declined in morphological indices more precipitously; these differences were significant in ΔWt and ΔK. Animals in loud tanks demonstrated significant and variable heterophilia and significantly higher and more variable H:L ratios. Plasma cortisol concentrations were higher among animals in loud tanks. Kidneys were significantly more affected by parasites in loud tanks. Other physiological measures were unremarkable. Seahorses exposed to loud ambient noise in aquaria exhibit primary, secondary, and tertiary stress responses at behavioral and physiological levels, necessitating allostasis at costs to growth, condition, and immune status. Aquarists and aquaculturists are thus advised to incorporate soundproofing modifications during design and set-up of facilities to improve fish health, and growth in culture.

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