Salmon stress inherited from parents

Parents shape the lives of their children in countless ways. Even before we are born, the genetics and environment of our parents build the foundation of our future. That said, additional stress that parents experience during reproduction may influence the next generation of offspring. One stress event that uniquely impacts fish is catch-and-release angling – a conservation technique that encourages recreational fishing while maintaining productive fish populations. The idea is that many fish species can recover from the exercise, air exposure and potential injury; however, it remains unclear how catch-and-release angling during the spawning period, when fish reproduce, might affect developing eggs and subsequent offspring. Magdalene Papatheodoulou and colleagues at the University of Glasgow, UK, were particularly interested in how catch-and-release angling close to the spawning period of wild Atlantic salmon (Salmo salar) might impact the development of their offspring. Papatheodoulou and her colleagues predicted that salmon parents that experienced catch-and-release angling would produce offspring that were less likely to survive.To study this, the researchers captured 56 male and female salmon from the river Blackwater in Scotland before the spawning period. The team then transported the fish to holding tanks, where they chased some individuals around for 3.5 min before catching them and holding them in the air for 1–2 min, to mimic the stress of being caught by an angler. They also chased other fish around, to simulate the less stressful experience of being caught but escaping before they were reeled in, and another group of fish were just allowed to swim undisturbed. The fish then rested in the holding tanks for 8–18 days until they spawned, at which point the researchers mixed eggs and sperm from fish that were part of the study with gametes from fish that did not participate in any part of the study. This way, the researchers were sure that only one parent of the fertilized eggs was stressed. After monitoring the eggs through development at a nearby hatchery, the team transferred the fry back to the University of Glasgow where they could watch how the offspring grew and developed.As Papatheodoulou and her colleagues expected, the fertilized eggs of the stressed parents, which had been chased and held aloft, died at a greater rate than those of salmon that had been less stressed or not stressed at all. However, the fertilized eggs of parents that had been stressed 8 days before spawning survived much better than those of parents that had been chased and taken out of the water 18 days before they spawned, which suggests that catch-and-release angling may have less of an effect on egg development when the parents are caught close to spawning. And when the eggs hatched, the larvae produced by stressed parents had a higher death rate than those produced by unstressed parents, particularly following the outbreak of a fungal infection. Papatheodoulou thought this was especially interesting because stressing salmon parents seem to change the ability of the larva's immune system to fight fungal infection.In addition, the yolk sacs of the larvae produced by stressed mothers were smaller, resulting in fry that were smaller when they first began to feed. However, the offspring produced by stressed fathers were a normal size when they started feeding, which makes sense as mothers supply most, if not all, of the nutrients provided by egg yolk sacs.Overall, Papatheodoulou and her colleagues have shown that catching and releasing Atlantic salmon as they rush upriver to spawn impacts the next generation. It is essential to protect both sexes during the critical spawning window, which is important knowledge for fisheries managers to better safeguard salmon while spawning, possibly by closing the recreational fishing season before and during this crucial period.

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