Do you smell what I smell? Olfactory impairment in wild yellow perch from metal-contaminated waters.

In this study, we sampled yellow perch from three lakes along a metal-contamination gradient and examined their olfactory ability in response to conspecific chemical alarm cues and metal-binding characteristics of their olfactory epithelium (OE). We measured the electrophysiological response at the OE, tested their antipredator behaviour and measured neuronal density at the olfactory rosette and bulb. Yellow perch from contaminated lakes exhibited significantly larger electrophysiological responses to alarm cues than clean lake fish, but showed no antipredator behaviour contrary to clean lake fish. Neuron density did not differ at either the olfactory rosette or bulb between clean and contaminated fish. Unlike fishes raised under laboratory or aquaculture settings, fish from contaminated lakes possessed a functional OE after metal exposure, but similar to laboratory/aquaculture fishes, yellow perch did not exhibit olfactory-mediated behaviours. Thus, wild fish from contaminated lakes can detect chemical stimuli but olfactory signal processing is disrupted which could alter ecological functioning.

Branchial cadmium and copper binding and intestinal cadmium uptake in wild yellow perch (Perca flavescens) from clean and metal-contaminated lakes.

Branchial binding kinetics and gastro-intestinal uptake of copper and cadmium where examined in yellow perch (Perca flavescens) from a metal-contaminated lake (Hannah Lake, Sudbury, Ontario, Canada) and an uncontaminated lake (James Lake, North Bay, Ontario, Canada). An in vivo approach was taken for gill binding comparisons while an in vitro gut binding assay was employed for gastro-intestinal tract (GIT) uptake analysis. By investigating metal uptake at the gill and the gut we cover the two main routes of metal entry into fish. Comparisons of water and sediment chemistries, metal burdens in benthic invertebrate, and metal burdens in the livers of perch from the two study lakes clearly show that yellow perch from Hannah L. are chronically exposed to a highly metal-contaminated environment compared to a reference lake. We found that metal-contaminated yellow perch showed no significant difference in gill Cd binding compared to reference fish, but they did show significant decreases in new Cd binding and absorption in their GITs. The results show that gill Cd binding may involve low-capacity, high-affinity binding sites, while gastro-intestinal Cd uptake involves binding sites that are high-capacity, low-affinity. From this we infer that Cd may be more critically controlled at the gut rather than gills. Significant differences in branchial Cu binding (increased binding) were observed in metal-contaminated yellow perch. We suggest that chronic waterborne exposure to Cu (and/or other metals) may be the dominant influence in gill Cu binding rather than chronic exposure to high Cu diets. We give supporting evidence that Cd is taken up in the GIT, at least in part, by a similar pathway as Ca(2+), principally that elevated dietary Ca(2+) reduces Cd binding and uptake. Overall our study reveals that metal pre-exposure via water and diet can alter uptake kinetics of Cu and Cd at the gill and/or the gut.

Brook charr alevins alter timing of nest emergence in response to chemical cues from fish predators.

Brook charr (Salvelinus fontinalis) lay their eggs in gravel nests called redds. The nests are not defended for extended periods and the eggs and young may be subject to predation from predators that travel through the substrate into the redd. In this study we tested whether long-term exposure of brook charr eggs to chemical cues from predatory sculpins (Cottus cognatus) resulted in an adaptive shift in the timing of emergence of charr alevins from artificial redds. We reared brook charr eggs in the presence of chemical cues from sculpins fed brook charr eggs, sculpins fed brine shrimp, and a well water control. Significantly more alevins emerged during the first week of the emergence period when exposed to chemical cues from sculpins fed eggs than from cues from sculpins fed brine shrimp or from well water. Alevins that emerged sooner were smaller and possessed larger yolk sacs than alevins that emerged later in the emergence period. Our results suggest that alevins that emerge sooner may escape predation in the redd, but may pay a cost in being under-developed upon emergence into the open water of the stream or lake.

Are chemical alarm cues conserved within salmonid fishes?

A wide diversity of fishes possess chemical alarm signalling systems. However, it is not known whether the specific chemicals that act as alarm signals are conserved within most taxonomic groups. In this study we tested whether cross-species responses to chemical alarm signals occurred within salmonid fishes. In separate laboratory experiments, we exposed brook charr (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout (Oncorhynchus mykiss) to chemical alarm signals from each of the three salmonid species and from swordtails (Xiphophorus helleri). In each case, the test species responded with appropriate antipredator behavior to all three salmonids alarm cues, but did not react to swordtail cues. These data suggest that chemical alarm cues are partially conserved within the Family Salmonidae. For each species tested, the intensity of the response was stronger to conspecific alarm cues, than to heterospecific alarm cues, indicating that salmonids could distinguish between chemical cues of conspecifics versus heterospecifics. These results suggest that the chemical(s) that act as the alarm cues may be: 1) identical and that there may be other chemical(s) that allow the test fish to distinguish between conspecifics and heterospecifics, or 2) that the cues that act as signals are not identical, but are similar enough to be recognized.

Chemosensory assessment of predation risk by slimy sculpins (Cottus cognatus): responses to alarm, disturbance, and predator cues.

Slimy sculpins (Cottus cognatus) are small benthic fish that commonly co-occur with predatory fishes throughout most of their range in North America. In two laboratory experiments we examined the nature and extent of responses of slimy sculpins to chemosensory cues from predatory brook trout (Salvelinus fontinalis) and chemical alarm cues released by conspecific sculpins. Sculpins responded to three different classes of chemical stimuli: (1) cues of predatory brook trout, (2) damage-released alarm cues from conspecific sculpins, and (3) disturbance cues from conspecific sculpins. Sculpins did not distinguish between trout fed different diets; however, the presence of damage-released alarm cues did enhance the intensity of response to the predator chemicals. A histological analysis of the skin of sculpins revealed the presence of large sacciform cells that may act as the source of chemical alarm signals.

Importance of predator diet cues in responses of larval wood frogs to fish and invertebrate predators.

We examined the effects of predator diet on the antipredator responses of larval woodfrogs (Rana sylvatica). We found that tadpoles showed stronger responses to fish (Perca flavescens) that were fed tadpoles than those fed invertebrates. Similarly, we found that tadpoles responded more strongly to larval dragonflies (Anax spp.) fed tadpoles than to dragonflies fed invertebrates. The overall intensity of response of tadpoles to fish was much stronger than that to dragonflies. Predator diet effects are not ubiquitous in predator-prey systems. We discuss possible reasons why predator diet effects are seen in some, but not all, predator-prey systems.