Plasma levels of insulin and liver glycogen contents in one- and two-year old Atlantic salmon (Salmo salar L.) during the period of parr-smolt transformation

Abstract

Plasma levels of insulin were measured by specific radioimmunoassay in 1-year and 2-year old Atlantic salmon (Salmo salar) parr during the period of parr-smolt transformation. The two-year old fish were of two different categories; silvering pre-smolts and previously mature male parr. If insulin plays an important role in parr-smolt transformation and/or subsequent osmoregulatory changes it was expected that the pre-smolts would show a different insulin profile compared to the mature male parr and one-year old parr, both of which show impaired hypoosmoregulatory ability compared to smolts. Measurements were taken during two separate years. Between January and April both categories of two-year old fish had generally higher plasma levels of insulin compared to the non-smolting one-year old parr. In the pre-smolts insulin levels ranged from 4.0 to 7.9 ng ml(-1), and from 7.8 to 16.7 ng ml(-1) in 1990 and 1992 respectively, while in the previously mature males the same respective values were from 4.3 to 10.0 ng ml(-1), and from 6.6 to 24.1 ng ml(-1). In the two-year old fish, whether pre-smolts or mature males, plasma insulin levels peaked between 1-2 months before final smoltification, after which insulin titers declined sharply. In 1990, the 1-year old parr showed a dual peak in plasma insulin. Insulin first peaked in February (7.8 ng ml(-1)), and then again in April-May (7.7 ng ml(-1)), while in 1992 the 1-year old parr showed a number of smaller transient peaks (5-7 ng ml(-1)) between March-May, followed by sharp elevation of insulin levels in June. Liver glycogen contents were at their highest (3.5-5.0 g 100 g(-1) I liver wet weight) in March in both 1-year and 2-year old fish. Glycogen levels were low during the later stages of parr-smolt transformation, before rising again in June in both the 1-year old and precociously mature parr, but not in the smolts.

Growth and salt-water tolerance of juvenile Atlantic salmon, Salmo salar , reared under different combinations of dietary carbohydrate and photoperiod regime

“…It has been previously suggested that low glycogen levels may be a major reason for the high death rate when smolts are transferred from fresh to salt water (Mayer et al 1994;. During the seawater challenge test in the present study, the glycogen levels in the smolts (C10 Wi group) were reduced, by 47% in the liver and 7% in the muscle.…”

“…It has been previously suggested that low glycogen levels may be a major reason for the high death rate when smolts are transferred from fresh to salt water (Mayer et al . 1994; Plisetskaya et al .…”

Physiological Status of Naturally Reared Juvenile Spring Chinook Salmon in the Yakima River: Seasonal Dynamics and Changes Associated with Smolting

“…Growth hormone (GH) has been shown to be photoperiod responsive (Bjornsson et al 1989(Bjornsson et al , 1995McCormick et al 1995), and increases in GH have been found as early as March in fish held under natural photoperiods. In addition, an increase in plasma insulin has been found in coho salmon Oncorhynchus kisutch as early as February (Plisetskaya et al 1988) and in Atlantic salmon smolts in March (Mayer et al 1994). Increases in either GH or insulin have been suggested to promote growth (Mommsen 1998).…”

Examination of liver and muscle glycogen and blood glucose levels of Capoeta umbla (Heckel, 1843) living in Hazar Lake and Keban Dam Lake (Elazig, Turkey)

“…As liver gets bigger in fish due to age, liver glycogen amount also increases (Shahidi and Dujanski, 1993). Mayer et al (1994) determined the highest liver glycogen values as 35 mg/g in 1 year old and 50 mg/g in 2 years old of Salmo salar. Heinimaa (2004) stated that liver glycogen values of Atlantic salmon consists 0.5 to 9.5% of the liver weight.…”