A decrease in photoperiod shortly after first feeding influences the development of Atlantic salmon (Salmo salar)

Four groups of Atlantic salmon fry (n=2000) were exposed to continuous light (LD24:0) from first feeding on 18th April 2001, after which they were exposed to either an 8 or 12 week period of short days (LD10:14) starting on either the 21st May or the 18th June. Each group was then returned to LD24:0 until the conclusion of the experiment the following March. In August 200 fish per treatment were individually PIT tagged. All groups were maintained under an ambient temperature regime. The highest levels of sexual maturation in 0+ male parr were recorded in the 12 week/May group (>11% of the entire male and female population), with the lowest levels (6%) in the 8 week/May and 8 week/June groups (

The effects of daily ration on growth and smoltification in 0+ and 1+ Atlantic salmon (Salmo salar) parr

The effects of long-term variations in feed ration were studied during two experiments on Atlantic salmon parr. In the first experiment, three duplicate groups of approximately 500 salmon parr were fed at rates of 100%, 66% or 33% of the manufacturer’s recommendation from shortly after first feeding. Each group were exposed to a photoperiod regime which was expected to result in smoltification 9 months after first feeding. In the second experiment, three duplicate groups of 550 fish were fed 100%, 66% or 33% of the manufacturer’s recommendation from first feeding and exposed to a simulated natural photoperiod, which was expected to result in smoltification 13 months after first feeding. In both experiments fish size increased with ration, with recruitment to the upper modal group (UMG) of the population also related to ration (85-96%, 64-88% and 28-42% UMG fish for the full, two-thirds and one-third ration groups respectively, recorded at the conclusion of each experiment). Throughout each experiment the full and two-thirds ration fish maintained similar whole body lipid concentrations, although lipid concentrations in the one-third ration fish were generally lower. At the conclusion of experiment 1, gill Na+, K+-ATPase activity in UMG fish fed full rations reached 9.5 μmol ADP hydrolysed. mg-1. protein-1. h-1, whereas ATPase activities were lower in the other ration groups. In experiment 2, all groups had similar gill Na+, K+,-ATPase activities at the conclusion of the experiment (6.4-9.3 μmol ADP hydrolysed. mg-1. protein-1. h-1). Following 24h seawater challenges, conducted during the parr-smolt transformation, UMG fish from the full and two-thirds groups of experiment 1 displayed high survival rates (100%) and low serum osmolalities (335 mOsm.kg-1), with lower survival rates (75%) and higher serum osmolalities (370 mOsm.kg-1) recorded in the one-third ration fish. In experiment 2 similar survival rates (100%) and serum osmolalities (350 mOsm.kg-1) were found in all ration groups. It is concluded that under accelerated production regimes, feed restriction may result in underyearling Atlantic salmon smolts developing a poor hypo-osmoregulatory ability. Variations in ration significantly influence growth, although it is believed that growth is dependant on the maintenance of a specific lipid level in the body

Modification des taux seriques de gonadotropine, oestradiol 17 beta et vitellogenine pendant les premiers cycles de reproduction de la truite arc en ciel femelle

International audienceThe present study investigates the relationship between changes in serum levels of gonadotropin, oestradiol 17β and vitellogenin (by measurement of phosphoprotein phosphorus and calcium) during the annual reproductive cycle of the female rainbow trout. Two series of experiments were conducted: the first using 2-year-old previously immature fish, and the second using 3-year-old trout which had spawned during the previous reproductive cycle. The fish were maintained throughout the experiments in light-proof aquaria under simulated normal seasonal light cycles at a constant temperature of 9°C and feeding rate of 0.5% body weight/per day. The fish in both series of experiments spawned by hand-stripping in mid-January at exactly the same time as other fish maintained in outside tanks under ambient conditions. Thus, photoperiod is confirmed as the major environmental determinant of reproduction in rainbow trout. A similar sequence of neuroendocrine changes was observed in both the first- and second-time spawning fish, thus indicating that similar pituitary-ovarian control mechanisms are in operation in all maturing fish irrespective of age. The initial endocrine event was an increase in the serum level of gonadotropin during the first stages of oocyte development. In the second series of experiments, which were begun in February, it appeared that minor alterations in both gonadotropin and oestradiol 17β levels were occurring as early as March in the annual cycle. Following these changes in gonadotropin, oestradiol 17β levels were increased to reach a maximum in the summer during the period of active exogenous vitellogenesis. After the subsequent induction of vitellogenin secretion, as evidenced by raised calcium and phosphoprotein phosphorus levels, oestradiol 17β values fell and this decrease appeared to elicit a much greater increase in gonadotropin levels at the time of final oocyte maturation, ovulation and spawning. Vitellogenin levels did not fall until spawning had occurred. The relationship of these changes to the overall control of trout reproduction is discussed

Relationships between serum levels of gonadotropin, oestradiol-17β, and vitellogenin in the control of ovarian development in the rainbow trout

The present study investigates the effects of seasonally changing photoperiod regimes on the levels of serum gonadotropin, oestradiol-17/3, and vitellogenin (as indicated by phosphoprotein phosphorus and calcium measurements) on the time of spawning of female rainbow trout (Salmo gairdneri). This included a control regime and also seasonal cycles in which the increasing and decreasing components of the photoperiod were maintained but compressed into 6- and 9-month periods. Spawning in the control fish occurred in mid- January at the same time as fish in outside ponds under ambient conditions, whereas under the 6- and 9-month cycles it was advanced by approximately 12 and 6 weeks, respectively. Under both the control and experimental regimes, the primary change was an increase in serum levels of gonadotropin during the early stages of ovarian development, after which levels were reduced. This was followed by increased oestradiol-17β levels which became particularly pronounced during the period of exogenous vitellogenesis. These changes in oestradioL17β appeared to stimulate vitellogenin production and release by the liver as evidenced by increases in serum calcium and phosphoprotein phosphorus levels. Subsequently, vitelogenin levels remained high until after spawning was complete. During the later stages of ovarian development oestradiol levels fell, thus signalhng, probably by a negative feedback mechanism, a further and larger increase in gonadotropin levels presumably required for the control of fmal oocyte maturation and ovulation. This sequence of endocrine changes was similar under the shortened photoperiod cycles, although modifications were apparent in both their timing and duration, resulting in earlier spawning times