Behavioral Responses of Mosshead and Woolly Sculpins to Increasing Environmental Hypoxia

Behavioral responses of the rocky intertidal mosshead sculpin (Clinocottus globiceps) and woolly sculpin (Clinocottus analis) to increasing environmental hypoxia (low PO₂) were observed in a seawater aquarium with a depth gradient. The experimental design allowed observation of the response of these animals to encroaching environmental hypoxia. We observed three behaviors by which the fish dealt with hypoxia: emergence from substrate (EFS), first avoidance response (FAR), and aquatic surface respiration (ASR). With respect to EFS and FAR, mosshead sculpins were more labile in their responses than woolly sculpins. However, the mean PO₂ at which ASR was initiated was statistically indistinguishable between species. We suggest that the differences we observed represent alternate behaviors by which these related species deal with the trade-off imposed by the simultaneous needs to avoid predation and optimize respiration. We further suggest that these alternate behaviors have evolved around a conserved physiological constraint, the PO₂ at which ASR must be performed.

Fig. 1.

The experimental aquarium. Nitrogen was introduced to the tank via the diffuser. Each sampling tube was attached to a three-way stopcock for water analysis. The sides and back of the aquarium were insulated with aluminized bubble wrap (not shown), and a grid was drawn on the front of the aquarium to record location of fish (not shown)

Fig. 2.

A graphical model depicting the hypothesized relationship between perceived risk, water PO₂, and aquatic surface respiration (ASR) behavior in tidepool-inhabiting sculpins. At low levels of perceived risk, fish are expected to perform ASR as needed to optimize respiratory oxygen intake. At high levels of perceived risk, fish are expected to perform ASR as demanded by some physiological threshold PO₂ below which the behavior must be performed. At some threshold level of risk, fish are expected to put off ASR until physiological demands provide motivation to perform the behavior

Received: 27 Mar 2002

Accepted: 15 Oct 2002