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.

Large, predatory, non‐indigenous species such as the cladoceran, Bythotrephes longimanus, can have a profound effect on aquatic food webs, but determining the prey consumed by such species is problematic because they shred prey externally and consume only soft body tissues. We assessed the usefulness of an immunochemical approach, in which putative zooplankton prey were homogenized and polyclonal antibodies against total proteins were raised in rabbits and purified against predator proteins. Using either dot‐blot or enzyme‐linked immunosorbent assay‐plate formats, assays easily detected prey proteins in single B. longimanus. Issues encountered included some degree of cross‐reaction with predator proteins and among prey species for some antisera and questions concerning determination of a correct blank value for assays, however, there are feasible approaches to resolving these issues. Immunochemical assays were readily applied in to a total of 185 individual B. longimanus in the Lake Michigan pelagic ecosystem in summer of 2008 and 2009 and indicated ingestion of cladoceran and copepod species, typically described in the literature, but also dreissenid veliger larvae and the large copepod Limnocalanus macrurus, not usually considered prey for Bythotrephes. Assays results showed some degree of correlation with numerical abundances of zooplankton prey in the water column, suggesting generalist feeding. Protein immunochemical assays offer a quick, sensitive and practical approach to examining planktonic food‐web questions that are compatible with, but have certain advantages over, alternatives such as nucleic acid techniques.