Seawater tolerance in captive high-Arctic Svalbard charr (Salvelinus alpinus): effect of photoperiod and body size

Abstract

Anadromous Arctic charr (Salvelinus alpinus) returning after spending summer at sea were captured in a fish trap in the Dieset River on Spitsbergen (79°10′N), Svalbard. Fish selected for breeding were transported to Trondheim in mainland Norway. Eggs obtained from the charr were fertilized and incubated in total darkness. First-fed alevins and resulting parr were kept under continuous light until an age of 0+ and 1+ years, respectively. Some 1+ charr were kept as controls under a continuous short-day photoperiod (6L:18D) from autumn until the end of the experiment the following July. Charr aged 0+ and 1+ years old were exposed to a short-day photoperiod from October until January and a simulated natural photoperiod for 80°N from January until the end of the experiments. Challenge tests demonstrated a size-dependent seawater tolerance for charr with a body length less than 18 cm. Fish smaller than 12 cm did not survive the 96-h test period. The larger charr kept under simulated natural photoperiod developed increased hypoosmoregulatory capacity. Charr kept under short-day treatment showed a slight, short-lived increase in seawater tolerance. A 7-days seawater challenge test at the end of the experiment (July) demonstrated that the anticipatory seawater preparation in charr is influenced by photoperiod. We conclude that offspring from anadromous high-Arctic charr must achieve a threshold body size (>25 cm) before they can respond to photoperiod signals which trigger the development of the hypoosmoregulatory capacity typical for smoltifying salmonids.