M.J.R. Porter

Dietary lipid enhancement of broodstock reproductive performance and egg and larval quality in Atlantic halibut (Hippoglossus hippoglossus)

Abstract Two series of experiments were conducted to assess whether the trash fish-based diet traditionally used by the industry for broodstock halibut could be replaced by a formulated pelleted feed and to investigate the effects of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (AA) on halibut fecundity, blastomere morphology and fertilisation and hatching rates. In the first experiment, two formulated broodstock feeds (one containing Krill meal and one supplemented with tuna orbital oil, which provided higher dietary levels of DHA and AA), gave similar performances (Relative fecundity 9557±3462 and 10,551±2166, fertilisation rate 40.0±6.4% and 40.0±9.1%, respectively) to that of a fish fed a trash fish-based diet (Relative fecundity 11,782±1873, fertilisation rate 41.0±4.0%). In a second experiment, the spawning performance and egg quality of two groups of broodstock maintained on two formulated diets, each containing different levels of AA (1.8% and 0.4%) was compared over two successive spawning seasons. The diet with the higher (1.8%) level of AA resulted in significantly higher ( p

The use of cage lighting to reduce plasma melatonin in Atlantic salmon (Salmo salar) and its effects on the inhibition of grilsing

The effects of additional night time illumination on circulating plasma melatonin levels and maturation were studied in Atlantic salmon maintained in sea cages under commercial conditions. Salmon subjected to additional night-time lighting from November to July had significantly lower dark phase melatonin levels (303.1 ± 6.3 pg/ml) compared to control fish (600.0 ± 53.0 pg/ml) maintained under ambient photoperiod. More importantly, as far as the commercial farmer is concerned, only 6.1% of the group exposed to additional lighting matured compared to 61.5% of the fish in the control group. It is suggested that the clear effect of the additional lights on reducing grilsing in Atlantic salmon is mediated through a reduction in the amplitude of plasma melatonin below a putative threshold level during the subjective dark phase.

The role of melatonin and the pineal gland on development and smoltification of Atlantic salmon (Salmo salar) parr

Abstract The present work used measurements of plasma melatonin throughout the year, pinealectomy, and/or intramuscular melatonin implants to investigate the role of melatonin and the pineal gland as intermediaries in the transfer of photic information on daily and calendar time in the control of the timing of the parr–smolt transformation in the Atlantic salmon. An initial experiment confirmed the presence of a seasonally changing light–dark rhythm of melatonin in potential S2 Atlantic salmon smolts, the profile of which accurately reflected the dark phase throughout the annual photoperiodic cycle. In the second experiment, potential S1 smolts were implanted and/or pinealectomised at the winter solstice. Although no variations in growth were observed between groups, smoltification in the pinealectomised plus implanted group was advanced by 3 weeks while the onset of smoltification in the pinealectomised fish was delayed by 3 weeks. In the final experiment, Atlantic salmon parr (3.5–7.0 g) which received melatonin-implants in June were significantly larger than the controls 1 month after implantation; this resulted in all the implanted fish entering the upper modal group by the time of smoltification whereas the control groups exhibited clear bimodal distributions. These results suggest that melatonin implantation and/or pinealectomy can alter the timing of seawater adaptation. Additionally, melatonin was shown to significantly alter the population structure of sibling Atlantic salmon parr resulting in 92% of individuals becoming S1 smolts. However, the mechanism(s) by which the pineal may influence development remains unclear.

Physiology during smoltification in Atlantic salmon: effect of melatonin implants.

Melatonin implants were used to override natural melatonin rhythm in groups of juvenile Atlantic salmon, Salmo salar, raised at simulated natural photoperiod (SNP) and constant light (LL) from mid-March until end of August. The experiment contained also both sham control (with non-melatonin implants) and control (no implants). No differences were found in the experimental variables between these two control groups. Growth and food intake were negatively affected by melatonin implantation. Overall, higher GH levels were observed in the SNP melatonin-implanted group, whereas no differences in GH levels were seen between the SNP control, LL control, or the LL melatonin-implanted groups. Highest food intake was seen in the LL control group. No differences in food intake were recorded between the LL melatonin-implanted and SNP control groups. Gill Na+, K+, ATPase (NKA) activity was influenced by time as well as the interaction between photoperiod and time. No differences in gill NKA activity or plasma chloride levels following transfer to seawater were seen between the groups with melatonin implants and their controls. Based on the present results, it seems apparent that melatonin does play a role in regulating food intake and growth in Atlantic salmon smolts.

The interactions of photoperiod and insulin-like growth factor-I (IGF-I) in the control of rainbow trout reproduction

First-time maturing female rainbow trout maintained under an advancing photoperiod regime exhibited a different plasma IGF-I profile relative to those under a natural photoperiod.

Seasonality of oocyte development and pigmentation in Atlantic salmon, Salmo salar

This study identifies the presence of a spring drop of flesh pigmentation that coincided with oocyte atresia in Atlantic salmon and outlines the potential influence that additional lighting and feed management strategies can have on these processes.