Assessment of osmotic adaptation and seawater readiness in juvenile Chinook salmon reared at the Malkinskiy salmon hatchery

Aim: to assessed the readiness of Chinook salmon fingerlings reared at the Malkinskiy salmon hatchery (Kamchatka region) to seawater run and to reverse water-salt transport; to develop a rapid and effective method to determine the readiness of juvenile Chinook salmon to seawater run.Methods: the dynamics of haemoglobin, glucose, haematocrit, blood osmolarity and body weight were studied in juvenile of Chinook salmon of a different sizes exposed in water with salinities of 30 and 40% (experiments in fresh water under the same conditions served as a control, all experiments were carried out in three repetitions).Novelty: a method is described to assess the readiness of juvenile salmonids with a prolonged freshwater period of life to sea water run.Results: the standard “salinity test” does not always reflect the readiness of juveniles to run, and to clarify their physiological state, it is worth studing the dynamics of blood osmolarity during exposure to water with a salinity of 30% (the critical indicator is 340 mOsm l‑1 after a day of experiment). Blood levels of glucose, hemoglobin and hematocrit, as well as the dynamics of body weight are not suitable for assessing salt resistance because off the excessive sensitivity of these indicators. It was shown that juvenile Chinook weighing ≥ 7 g were physiologically ready for run, whereas juveniles weighing ≤ 5 g were not. The intermediate group (5–7 g) exhibited different physiological states in different years.Practical importance: determining the minimum size of fully transformed smolts and finding ways to increase the salt tolerance of juveniles is the way to increase the profitability of the hatchery.