Reflex impairment can measure sublethal effects of temperature, hypoxia, and injury

Epaulette shark, Aquarium

The epaulette shark is a tropical reef shark that can live in an environment with cyclical periods of low oxygen concentration and high temperature (Wise et al. 1998). After exposure to hypoxic conditions, epaulette shark reflex actions were tested, including righting, response to touch, rhythmic gill movements, rhythmic swimming, and movement of diagonally opposed fins for locomotion. Reflex actions were not impaired by hypoxia, suggesting that animals were adapted to reef conditions and would not show maladaptive responses to hypoxia. Subsequently, this species was found to have important adaptations to hypoxia (Soderstrom et al. 1999, Hickey et al. 2012).

Animal responses to stressors can be adaptive or maladaptive. When animals are exposed to stressor types or intensities for which they are not adapted, stress responses can be too much of a good thing. Adaptive responses help the animal move away from and avoid stressors to return to normal unstressed behavior and homeostatic states. Maladaptive responses cause the animal to become more stressed and eventually can result in morbidity and mortality. 

Adaptive and maladaptive responses of crustaceans to stressors and stress, Stoner 2012

Reflex impairment is an ecologically relevant measure of vitality loss, fitness, and the spectrum of adaptive and maladaptive responses to stressors. Measurement and summation of a suite of reflex actions (as in the case of RAMP or barotrauma modified RAMP) is a powerful means for testing experimental hypotheses about the effects of stressors on animals. For aquatic animals, temperature (elevated or depressed), hypoxia, and injury are important master variables associated with stress induction (Davis 2002, Suuronen 2005, Gale et al. 2013).

The key to testing for vitality, stress, and fitness using reflex actions or barotrauma symptoms is to derive an emergent index for reflex impairment by summing presence or absence of many individual actions or symptoms. The resultant emergent impairment index (RAMP) is a powerful synthesis of the many mechanistic systems (behavior, physiology, neural, muscle, organ) that have been identified in a whole animal. RAMP expresses, with quantitative data, the resultant vitality and health state of the animal.

Some examples of relationships between reflex impairment and temperature, hypoxia, and injury are illustrated below. In these examples reflex impairment was significantly different among stressor treatments and was related to the severity of stressors.

Reflex impairment in crabs exposed to low temperature, Stoner 2009

Reflex impairment in Atlantic cod exposed to hypoxia, Humborstad et al. 2009

Reflex impairment in coho salmon exposed to hypoxia, Raby et al. 2012

Reflex impairment in sockeye salmon exposed to injury from different gear types, Donaldson et al. 2012

Reflex impairment in blue rockfish exposed to injury from barotrauma, Hannah et al. 2008