Abstract
ABSTRACT Considering that the anti-predation behaviour of prey fishes may vary with predator hunting strategy, we experimentally investigated the physiological responses of Astyanax bimaculatus (Linnaeus, 1758) shoals to the presence of two piscivorous fish species with different hunting modes: sit-and-wait and active pursuit. In addition, we evaluated the influence of underwater visibility conditions on the interaction between predator and prey. We tested the hypotheses that: (i) prey plasma cortisol and glucose levels vary according to piscivore hunting strategy, and (ii) no reduction in plasma glucose and cortisol levels takes place in turbid environments due to the inability of prey to accurately recognise predators by non-visual signals. The results revealed that the presence of piscivorous fish increased plasma cortisol levels in prey, with no significant difference recorded between the two hunting strategy treatments. We also observed no significant change in plasma glucose levels in different water transparency conditions. Thus, we conclude that physiological changes in the selected prey fish do not vary with predator hunting mode, and it is therefore necessary to consider the ability of the prey to recognise and evaluate danger, regardless of piscivore hunting strategy.
Highlights
Considering that the anti-predation behaviour of prey fishes may vary with predator hunting strategy, we experimentally investigated the physiological responses of Astyanax bimaculatus (Linnaeus, 1758) shoals to the presence of two piscivorous fish species with different hunting modes: sit-and-wait and active pursuit
When faced with piscivorous fish, regardless of their hunter strategy, plasma cortisol levels in A. bimaculatus shoal members increased by 90% on average, from 28.2 ng/ml in the absence of predators to 51.2 ng/ml with predators present
We observed that the sit-and-wait piscivore (H. aff. malabaricus) remained motionless for most of the experimental period, causing the prey fish shoal members to remain on the opposite side of the tank in a surveillance state, largely immobile
Summary
Considering that the anti-predation behaviour of prey fishes may vary with predator hunting strategy, we experimentally investigated the physiological responses of Astyanax bimaculatus (Linnaeus, 1758) shoals to the presence of two piscivorous fish species with different hunting modes: sit-and-wait and active pursuit. The results revealed that the presence of piscivorous fish increased plasma cortisol levels in prey, with no significant difference recorded between the two hunting strategy treatments. Os resultados evidenciam que a presença de peixes piscívoros aumenta os níveis plasmáticos de cortisol das presas, mas não houve diferença significativa entre os tratamentos com piscívoros de diferentes estratégias de caça. As part of this primary response the hypothalamic-pituitary-interrenal axis is activated, resulting in increased plasma levels of glucocorticoids such as cortisol. If primary and secondary responses persist chronically, tertiary responses may occur that are associated with deleterious effects, including a reduced growth rate, a reduction in the activity or efficiency of the immune system (immunosuppression) and the inhibition of reproduction (Barton, 2002)
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