Role of Fat Stores in the Maturation of Male Atlantic Salmon (Salmo salar) Parr

Abstract

We provide evidence that in male Atlantic salmon (Salmo salar) parr, maturation is suppressed when mesenteric fat fails to exceed an undefined level by May. In nonmaturing parr the postwinter increase in total lipids began in May, while the mesenteric store started filling in June. However, in male parr which would have matured, total lipids started increasing a month earlier, in April, and the mesenteric store started filling in May. Consequently, maturing male parr had significantly more mesenteric fat than nonmaturing fish by June. Mesenteric fat is needed for maturation. Levels continued to increase in nonmaturing parr during autumn months, but had declined in maturing parr by September. This depletion of mesenteric fat in maturing males coincided with increases in the gonadosomatic index from 0.05 to 10% and with reductions in both feeding and growth. Fasting during spring months delayed increases in total lipids and fat accumulation into the mesenteric store until June and suppressed maturation rates of male parr. The internal decision to suppress maturation is therefore dependent on mesenteric fat levels increasing in May. However, this requires the prior replenishment of other stores in April. A model is proposed to explain the physiological link between fat accumulation during spring and the initiation of maturation.

Body size versus gonad maturation form in under-yearling precocious males of the sea trout (Salmo trutta m. trutta L.)

“…Fat deposits, too, may play a role in determining whether or not some vertebrates are ready to mature [42,43]. Some authors are of the opinion that only those fish that have accumulated suitable energy reserves [12,19,44] or visceral fat [45,46] will start maturing. According to Silverstein et al [47] an effect in fat content is more distinct in smaller fish.…”

“…For instance, the Atlantic salmon will re-mature only when fat reserves are replenished by the spring (May). Fat depletion lasting until May results in a failure to mature in that year [46].…”

Photoperiodic effects on precocious maturation, growth and smoltification in Atlantic salmon, Salmo salar

“…The manipulation of environmental parameters such as temperature (Adams and Thorpe, 1989), photoperiod (Adams and Thorpe, 1989) and feed availability (Rowe et al, 1991;Berglund, 1995) at seasonally critical times, has resulted in reduced parr 4 maturation. Photoperiod manipulation is the tool most used by farms to control growth, reproduction and smoltification (Hansen et al, 1992;Thrush et al, 1994;Duncan et al, 1998;Porter et al, 1999;Endal et al, 2000).…”

Lipid content in rainbow trout (Oncorhynchus mykiss) fry and parr reared in spawning tributaries of Lake Taupo, New Zealand

“…Stored lipids are thought to be the main source of energy for fish during the winter starvation period (Black & Love 1997) and also during gonad development before reproduction (Shulman 1974;Rowe et al 1991). Overwintering mortality is higher for young salmonids with low fat reserves (Gardiner & Geddes 1980;Toneys & Coble 1980;Elliott 1993) especially during the early part of winter (Smith & Griffith 1994 for mitigation purposes, the amount of energy reserves could be a crucial factor for survival in the natural environment.…”