Effect of long-term pinealectomy on growth and precocious maturationin Atlantic salmon, Salmo salar parr

Department of Zoology, Stockholm University, 106 91 Stockholm, Sweden

Received: 8 February 2000
Accepted: 15 May 2000

Abstract

While the pineal organ in poikilothermic vertebrates consistently influences a number of physiological processes, its precise role, and what controlling signal (hormonal and/or neural) is abolished by its removal, is still uncertain. For this reason, the effect of long-term pinealectomy (PINX) on seasonal growth and reproductive development was investigated in Atlantic salmon, Salmo salar, parr. Mean daytime plasma melatonin level in the control, sham-operated and PINX fish was 35 pg·mL^–1 in all groups, while mean night-time levels were 296, 255 and 25 pg·mL^–1, respectively, indicating that PINX abolished the natural nocturnal rise in melatonin. Pinealectomy did not influence the incidence or timing of early sexual maturation in the male parr. However, pinealectomy significantly affected growth, its effect being boldly seasonally dependent. Compared to sham-operated and control fish, pinealectomized fish showed significantly lower specific growth rates (SGRs) during the period of lengthening photoperiod up until the summer solstice. Thereafter, corresponding to the season of decreasing photoperiods, the pinealectomized fish exhibited higher SGRs. These results suggest a functional relationship between the pineal organ and somatic growth in the Atlantic salmon, although what controlling signal from the pineal (melatonin or neural) is involved has yet to be determined.