Detection of conspecific alarm cues by juvenile salmonids under neutral and weakly acidic conditions: laboratory and field tests

Abstract

A variety of fishes possess damage-released chemical alarm cues, which play a critical role in the detection and avoidance of potential predation threats. Recently, we have demonstrated that the ability of fathead minnows ( Pimephales promelas) and finescale dace ( Phoxinus neogaeus) to detect and respond to conspecific alarm cues is significantly reduced under weakly acidic conditions (pH 6.0). Rainbow trout ( Oncorhynchus mykiss) and brook charr ( Salvelinus fontinalis) possess an analogous alarm cue system. However, it is unknown if the trout alarm cue system is likewise affected by relatively small changes in pH. In addition, previous studies have not verified this phenomenon under natural conditions. We conducted laboratory and field trials to examine the potential effects of acute exposure to weakly acidic (pH 6.0) conditions on the detection and response of conspecific alarm cues by juvenile trout. Our laboratory results demonstrate that while juvenile rainbow trout exhibit significant increases in antipredator behaviour under normal pH conditions (pH 7.0-7.2), they do not respond to the presence of conspecific chemical alarm cues (i.e. response is not different from controls) under weakly acidic conditions. Similarly, a wild strain of brook charr in their natural streams near Sudbury, Ontario, failed to detect conspecific alarm cues in a weakly acidic stream (mean pH 6.11) while they responded to these cues in a neutral stream (mean pH of 6.88). This is the first demonstration that relatively small changes in ambient pH can influence alarm responses under natural conditions. These data suggest significant, sub-lethal effects of acid precipitation on natural waterways.

Effects of acidification on olfactory-mediated behaviour in freshwater and marine ecosystems: a synthesis

“…Experiments with freshwater fish have demonstrated a range of behavioural and ecological changes associated with the impairment of olfaction and chemical cues detection under weakly acidified conditions (approx. pH 6.0) [20,37,38]. Recently, a very similar range of behavioural changes has been observed in experiments with marine fish exposed to predicted future changes in ocean pH due to rising atmospheric CO 2 [39,40].…”

“…These behavioural responses to alarm cues have been observed in a range of freshwater fishes, including fathead minnows (Pimephales promelas), finescale dace (Phoxinus neogaeus), pumpkinseed (Lepomis gibbosus) and rainbow trout (Oncorhynchus mykiss) [20,37,44]. However, predator avoidance behaviour was diminished or absent when these alarm cues were presented in experimental treatments acidified using a minute amount of sulfuric acid (often a major contributor to freshwater acidification) [20,38,45]. Furthermore, behavioural responses to basic chemical stimuli from food (amino acids) were significantly reduced under a similar range of pHs (e.g.…”

“…For many aquatic organisms, one of the main consequences of non-lethal acidification of aquatic ecosystems may be the disruption of olfaction and chemosensory abilities [20,21]. The detection of chemical cues and signals by olfactory and gustatory receptors plays a central role in the decision-making process [22], especially in structurally complex or turbid environments or under low light conditions [23 -25].…”

Reduction in activity by noxious chemical stimulation is ameliorated by immersion in analgesic drugs in zebrafish

“…Specifically, exposure to acidic compounds can cause stress in fish if this falls below normal tolerance levels through gill and epidermal damage. This may lead to problems with osmoregulation and oxygen uptake (Branson, 1992) and changes in behaviour (Brown et al, 2012;Leduc et al, 2004). Reilly et al (2008) have previously reported that both zebrafish and rainbow trout show behavioural responses after subcutaneous injection of dilute acetic acid.…”

Blinded by the stink: Nutrient enrichment impairs the perception of predation risk by freshwater snails

“…Ocean acidification associated with increasing atmospheric concentration of carbon dioxide and acidification of lakes and streams by sulfur and nitrogen deposition are two well known examples. Chemoreception in fish (Smith and Lawrence 1988, Brown et al 2002, Leduc et al 2004) and crayfish (Allison et al 1992) is impaired in weakly acidified streams. Similarly, marine fish reared in acidified seawater fail to respond appropriately to predator cues (Dixson et al 2009).…”