Cortisol and catecholamine responses to social context and a chemical alarm signal in juvenile lake sturgeon,Acipenserfulvescens

Abstract

We examined potential benefits of group living in juvenile lake sturgeon (Acipenser fulvescens Rafinesque, 1817) and whether those benefits applied equally to associations with conspecific and allospecific individuals. In the first experiment, one focal lake sturgeon was placed with either seven size-matched conspecifics, allospecifics, or in isolation and given a 30 s air exposure. In the second experiment, one focal lake sturgeon was placed with either seven conspecifics or in isolation and was exposed to a conspecific skin homogenate as a potential alarm substance or a control of distilled water. Cortisol, norepinephrine, and epinephrine levels were measured before and after exposure in each experiment via an indwelling cannula in the caudal sinus. In the first experiment, lake sturgeon held with allospecifics and in isolation had a significantly longer norepinephrine response. Furthermore, plasma norepinephrine concentration in the focal lake sturgeon in the allospecific treatment was significantly higher than the other treatments following air exposure. In the second experiment, there was no behavioural or hormonal response to the introduction of conspecific skin homogenate, yet isolated fish had elevated baseline norepinephrine and cortisol levels. Finally, comparison of baseline levels of all three hormones between two ages of juveniles indicated an effect of age on baseline epinephrine levels. Our findings confirm the potential physiological benefit of group living in lake sturgeon and suggest an ontogenetic shift in both the behavioural response to potential stressors and the baseline hormonal levels that may influence fitness.

Conspecific injury raises an alarm in medaka

“…2; M-W U = 0, p < 0.001) indicates that the process of behavior recording is in itself stressful, and exposure to CSE is an additional stressor. Activation of the primary stress response pathway in reaction to CSE exposure, as seen in medaka, has also been reported in many other species4142435152. There are examples, however, ( Brycon cephalus and Rhamdia quelen ) where conspecific injury elicits an anti-predator behaviour, but cortisol changes are undetectable5354.…”

“…Cortisol levels change via activation of the hypothalamus-pituitary-interrenal axis and peak within 15 minutes3940. Exposure to CSE can be a stressful event for some fish414243. I asked if behavioral changes in experimental subjects, described above, is accompanied by changes in cortisol levels.…”

“…There are examples, however, ( Brycon cephalus and Rhamdia quelen ) where conspecific injury elicits an anti-predator behaviour, but cortisol changes are undetectable5354. It is possible that alternate stress response pathways are triggered in some species, or in specific contexts643. It is also conceivable that detection thresholds in cortisol changes are subject to technical limitations as stess due to experimental processes may mask the stress from CSE exposure.…”

Comparative Studies of Several Physiologic and Biochemical Indexes of Wild Type and Hatchery-Bred Sturgeons in the Early Ontogenesis

“…This level is upregulated in the course of their maturation, indicating to necessity of being in permanent state of activity and alertness to confront possible aggression [35]. Moreover, in the model experiments with artificial upregulation of noradrenergic system in the brain structures, linear correlation between level of noradrenalin in the brain and level of social avoidance was revealed [35,36]. In the juveniles, bred in the pools, in conditions of food abundance and lack of predators, low levels of noradrenalin in the brain, really suppressing completely the state of alertness and reaction of escape from predators, are noticed.…”

“…Need in socialization and defence against aggression in this age in the sturgeons are considered as secondary issues [35] and, first of all, in this case changes of the level of salinity and hydrodynamic regime of living milieu have mostly their effects [46][47][48][49]. So, our studies have shown that while breeding of sturgeon fishes of certain region under the hatchery conditions, their biological peculiarities of development in natural conditions should be taken into consideration and it is important to reveal critical periods of formation of the most important physiological functions of the organisms and input of environmental factors in these processes.…”