Fish immune and stress responses

We now understand in more detail that fish immunity is at the crossroads between reliance of the innate and adaptive immunity (Tort et al, 2003 Huntingford et al, 2006). Some fish have the capacity to produce specific antibodies but the range of antibodies produced is far less diverse when compared with mammals or birds (Press, 1998). One relatively common misconception among non-specialists is that this reliance on the innate immunity is in some way less effective than a reliance on specific antibodies. The prevalence and diversity of invertebrates (98% of animal species) and fish (more than half of all vertebrates), in addition to their persistence through evolutionary history (Coelacanth relatively unchanged for 400 million years Johanson et al, 2006), demonstrate beyond any reasonable doubt that the innate immune system is very effective. 

Although the neural endocrine response to stress in fish is similar to that in mammals and is mediated through the HPA (or in fish hypothalamic-pituitary-inter-renal) axis, we now know that some aspects of the immune 

Reproductive success drives evolution, not the immediate health or welfare of the individual (Nesse, 1999, 2000, 2001). The stress response has to be viewed not just in relation to the individual but also in the context of benefits to the population and the species. The stress response may invoke physiological and behavioural changes that benefit long-term reproductive success but result in severe adverse consequences for the individual. This is most dramatically illustrated in some Pacific salmon, which individually suffer exhaustion, starvation and eventually death in order to reproduce as a species (McEwen Lasley, 2002). 

The stress response was previously viewed as a means to maintain homeostais however, the concept of homeostasis has largely been superseded by the concept of allostasis. Allostasis implies actively maintaining 

Rsh are commonly challenged by temperature extremes or rapid fluctuations these not only result in a stress response but have a profound effect on most metabolic processes (Ndong et al, 2007). 

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