Anaemia adjusts the aerobic physiology of snapper (Pagrus auratus) and modulates hypoxia avoidance behaviour during oxygen choice presentations

Abstract

SUMMARYThe effect of altered oxygen transport potential on behavioural responses to environmental hypoxia was tested experimentally in snapper, Pagrus auratus, treated with a haemolytic agent (phenylhydrazine) or a sham protocol. Standard metabolic rate was not different between anaemic and normocythaemic snapper (Hct6.7 and 25.7gdl -1 , respectively), whereas maximum metabolic rate, and hence aerobic scope (AS), was consistently reduced in anaemic groups at all levels of water P O2 investigated (P<0.01). This reduction of AS conferred a higher critical oxygen limit (P crit ) to anaemic fish (8.6±0.6kPa) compared with normocythaemic fish (5.3±0.4kPa), thus demonstrating reduced hypoxic tolerance in anaemic groups. In behavioural choice experiments, the critical avoidance P O2 in anaemic fish was 6.6±2.5kPa compared with 2.9±0.5kPa for controls (P<0.01). Behavioural avoidance was not associated with modulation of swimming speed. Despite differences in physiological and behavioural parameters, both groups avoided low P O2 just below their P crit , indicating that avoidance was triggered consistently when AS limits were reached and anaerobic metabolism was unavoidable. This was confirmed by high levels of plasma lactate in both treatments at the point of avoidance. This is the first experimental demonstration of avoidance behaviour being modulated by internal physiological state. From an ecological perspective, fish with disturbed oxygen delivery potential arising from anaemia, pollution or stress are likely to avoid environmental hypoxia at a higher P O2 than normal fish.

Fish physiology and ecology: the contribution of the Leigh Laboratory to the collision of paradigms

“…4). 2) Anaemic and normocythaemic fish avoid hypoxia at different levels but, interestingly, they leave low O 2 with similar levels of physiological perturbation suggesting that 'stress', rather than the absolute level of low O 2 , serves to trigger their avoidance reaction (Cook et al 2011).…”

“…SMR or minimum maintenance rate; Schurmann & Steffensen 1997;Cook et al 2011;Cook & Herbert 2012a) and the avoidance behaviour of P. auratus in different streams of O 2 -manipulated seawater was assessed using a large choice tank equipped with behavioural tracking software (Fig. 3) (Cook et al 2011(Cook et al , 2013Cook & Herbert 2012a, b).…”

“…4) (Cook et al 2011;Cook & Herbert 2012b). Pagrus auratus therefore appears to adopt a relatively high risk low O 2 strategy and would probably not fare well if low O 2 ever became frequent or widespread in coastal marine environments.…”

“…Moreover, by reducing the O 2 carrying capacity (i.e. anaemia state) of P. auratus with phenylhydrazine, two additional insights have been made (Cook et al 2011): 1) Anaemic fish reach their P crit limit at higher O 2 levels and also initiate avoidance at an earlier stage, indicating that additional stressors would probably sensitise the overall low O 2 reaction of P. auratus (see Fig. 4).…”

Low O2 acclimation shifts the hypoxia avoidance behaviour of snapper (Pagrus auratus) with only subtle changes in aerobic and anaerobic function

“…Reductions in locomotory activity and early avoidance of low O 2 represent two notable behaviours that would undoubtedly help to ensure the survival of fish facing hypoxic conditions Poulsen et al, 2011). Some fish engage these strategies before encountering their respective P crit (Herbert and Steffensen, 2005;Poulsen et al, 2011), but the New Zealand snapper (Pagrus auratus, Sparidae) does not show these responses (Cook et al, 2011). Snapper are late to leave hypoxic water because low O 2 avoidance commences below their P crit (Cook et al, 2011).…”