Effects of aquarium-related stressors on the zebrafish: a comparison of behavioral, physiological, and biochemical indicators.

Fishes in aquaria and aquaculture settings may experience a variety of stressors including crowding, different lighting, periods of food deprivation, and vibrations from sources including pumps and tapping of tank sides. The effects of such low-level chronic stress are poorly explored. We used replicate sets of six Zebrafish Danio rerio in four series of experiments to compare the effects of (1) stocking densities ranging from 0.13 to 1.2 fish/L, (2) cool white (6,500 K), warm white (4,100 K), and ultraviolet-enhanced (420 actinic) fluorescent lighting, (3) food deprivation for up to 9 d, and (4) random mechanical tapping on the tank side sufficient to induce a startle response on specific behaviors (fin display, body fluttering, aggression, mouth gaping, and chattering), dissolved cortisol released into aquarium water (collected on a chromatography column and analyzed with an immunoassay), and heat-shock proteins (HSPs 27, 40, 60, and 70) detected immunochemically in western blots of muscle tissue. Of all the treatments, only food deprivation resulted in significant differences between control and treatment fish; dissolved cortisol declined after 120 h of starvation and HSP40 and HSP60 in muscle tissue increased significantly after 216 h. High variability in behaviors and HSP measurements was noted within all controls and treatments, suggesting that effects of treatments were experienced unequally by individuals within a treatment. Social stressors resulting from dominance hierarchies may play a critical role in modifying the effects of aquarium and aquaculture stressors on captive fish.