Risk-induced early hatching in salmonids

Many ontogenetic niche shifts are phenotypically plastic and with their timing dependent on the perceived risks and benefits for the individual. In fish, hatching can be induced by oxygen shortage or the presence of egg predators or pathogens. However, little is known about the embryos' ability to avoid desiccation by hatching earlier. We simulated an increased risk by exposing some embryonated eggs to low water levels and compared them to control eggs kept deeper in the water. We tested eggs of arctic charr (Salvelinus alpinus), brown trout (Salmo trutta), and of small and large ecotypes of alpine whitefish (Coregonus sp.). During exposure, the apparently more risky environment induced higher rates of early hatching in all taxa tested. We suggest that the early hatching is either an adaptation of salmonids to risky environments or an accidental by-product that did not get counterselected because of its benefits to the fish larvae.