Ecological Effects on Food Utilization, Trypsin Isozymes, and Performance Qualities of Growth and Maturation in Northeast Arctic Cod (Gadus morhua L.)

ABSTRACT

The work demonstrates, for the first time, natural biological changes in fish during maturing processes using a unique combination of different biochemical techniques. Northeast Arctic cod caught by demersal trawls were studied in three Barents Sea areas during February–March 2008. Older larger cod from area A (between North Kanin Bank and Eastern Basin) had higher food utilization efficiency (with females showing highest white muscle protein synthesis capacity) than those from areas B (Kanin Bank) and C (Central Bank). Populations in areas A and C living in separate environments showed parallel regressions of pyloric caecal slope T/C ratio, with different elevations of trypsin specific activities and trypsin isozymes expressions. Approximately 30 trypsin isozymes were observed, with 13 isozymes of possibly exogenous trypsin isozyme fragments from prey items found at higher percentage of cod in areas A and B with higher food varieties. Larger maturing cod required higher energy from carbohydrate (probably phytoplankton), as amylase specific activity correlated with body weight. White muscle RNA levels were varied among females from different areas, but not among males. RNA and RNA/protein ratio levels were higher in oocytes than white muscle, and these levels decreased in higher developed oocytes. Oocyte trypsin-like specific activity in areas B < A < C (with oocyte T/C ratio in areas B > A > C) illustrated that females from area B (youngest with lowest oocyte protein turnover) had highest maturation rate, and would reach their spawning area(s) before those from areas A and C. Younger females (probably also males) living closer to coastal area with higher temperature and food varieties would reach sexual maturity faster than older cod and those living far from coastal area.