Evaluation of Seawater Adaptability of 0⁺ Japanese Char Related to Possibility of the Culture in Seawater

Abstract

The seawater adaptability of 0+ landlocked Japanese char Salvelinus pluvius was studied with mor tality, gill Na+-K+ATPase activity, and serum Na concentration, in order to evaluate the possibility of culture in seawater of this fish. When the fish (35 g) were transferred directly into seawater (the seawater challenge test), no mortality occurred even at 96 h after a direct transfer. The gill Na+-K+ATPase activ ity increased gradually, and the value at 96 h reached 4 times higher than the initial value. Serum Na concentration increased to about 180 mM at 24 h after transfer and, afterwards, the level showed no in crease until the end of the experiment. When the fish were reared in seawater over 100 days (the sea water rearing test), they grew from 35 g (Day 0) to over 90 g (Day 103). The gill Na+-K+ATPase activi ty at Day 103 was 9 times higher than the initial value. Serum Na concentration at Day 103 recovered almost to the initial value. These results suggest that the fish has acquired seawater adaptability in the size of 35 g and that this ability increased gradually while the fish were reared in the seawater environ ment. Since the fish can be transferred directly into seawater without any acclimation, it is possible to culture 0+ landlocked Japanese char in seawater.

Evidence of multiple migrations between freshwater and marine habitats of Salvelinus leucomaenis

“…Otherwise, the fish might have migrated downstream to an estuary or brackish water frequently from the freshwater environment during early life and prior to smoltification. Even in the early developmental stages before metamorphosis to smolts, the white‐spotted charr is euryhaline, having salinity tolerance because it is able to maintain ionic gradients between the body fluids and the external environment (Gorie, 1996; Takami, 1998). These findings suggest that the white‐spotted charr could migrate between freshwater and marine environments frequently throughout its life history.…”

Diverse migration patterns of anadromous white-spotted charr Salvelinus leucomaenis revealed from otolith microchemistry

“…Whitespotted charr with less sedentary behavior has been shown to cause downstream displacement (Yamada and Wada 2023). Furthermore, juvenile white-spotted charr exhibits seawater adaptability without acclimation (Gorie 1996;Takami 1998). Therefore, passively downstream-displaced whitespotted char may be able to survive in the sea even at the parr stage and return to rivers.…”

Variation in migratory history of Dolly Varden in a stream with an artificial dam in the Shiretoko Peninsula, Hokkaido, Japan

“…Many species of the genus Salvelinus have a high salinity tolerance at the under-yearling stage (e.g., Arctic charr, Dempson 1993; Zimmerman 2005, white-spotted charr, Gorie 1996), and also in the non-silver coloration form (e.g., Arctic charr, Gulseth et al 2001, brook charr, S. fontinalis, McCormick et al 1985, white-spotted charr, Takami 1998. Therefore, Dolly Varden may have the ability to survive in the sea even at a early stage.…”