Clive Randall

Broodstock management, fecundity, egg quality and the timing of egg production in the rainbow trout (Oncorhynchus mykiss)

Abstract The full potential of rainbow trout hatcheries can be attained only if the hatcheries can provide producers with regular supplies of high quality eggs and fry every week of the year. This review assesses aspects of brookstock management central to determining total number of eggs produced, quality of eggs, and timing of maturation and spawning. The effectiveness of hatchery programmes in supporting an expanding rainbow trout market is profoundly affected by the conditions under which the broodfish are maintained, their husbandry, and the stock selected for production. The paper examines factors that can critically affect fecundity, egg production, egg quality, spawning time, and maintenance of egg supplies. The discussion also outlines methods of manipulating spawning and areas requiring further advancement of knowledge if progress is to continue in optimising egg and fry production.

Molecular Characterization of Putative Yolk Processing Enzymes and Their Expression During Oogenesis and Embryogenesis in Rainbow Trout (Oncorhynchus mykiss)

Abstract Vitellogenin is the major yolk protein precursor in fish, but little is known about its processing pathway in the oocyte, nor about mobilization of yolk proteins during embryogenesis. In this study we cloned three putative yolk processing enzymes; specifically, cathepsin B and L, and lipoprotein lipase (LPL), from the rainbow trout ovary and determined their patterns of gene expression, together with cathepsin D, during oogenesis and embryogenesis using reverse transcription-polymerase chain reaction. The approximate sizes of both cathepsin B and cathepsin L transcripts were estimated as 1.7–1.8 kilobases by Northern blot analysis. Cathepsin D mRNA and cathepsin L mRNA were expressed constitutively throughout vitellogenesis and embryogenesis, showing the highest levels of expression at around fertilization. Cathepsin B and LPL were expressed exclusively during oogenesis. Quantitatively, expression of cathepsin D mRNA was higher than cathepsin B, cathepsin L, and LPL mRNA throughout the period studied. The different patterns of expression for these genes during oogenesis and embryogenesis signify specific temporal roles in yolk protein processing.

Central melatonin receptors in the rainbow trout: Comparative distribution of ligand binding and gene expression †

To better define the role of melatonin in fish, we have compared in detail the distribution of 2‐[125I]iodomelatonin binding sites with gene expression for melatonin receptor subtypes in a widely studied seasonal species, the rainbow trout. Three distinct partial sequences of the melatonin receptor gene were cloned from trout genomic DNA. Two of the sequences corresponded to the Mel1a receptor subtype, and one corresponded to the Mel1b receptor subtype. Analysis of numerous clones failed to find a sequence equivalent to the Mel1c receptor subtype. Comparison of receptor gene expression with 2‐[125I]iodomelatonin binding distribution indicated dendritic transport of the receptor. Melatonin receptors were associated predominantly with visually related areas of the trout brain, such as the thalamic region, the pretectal area, and the optic tectum. The pituitary was devoid of 2‐[125I]iodomelatonin binding, and melatonin receptor gene expression was not detectable. It would appear from the results of the present study that melatonin in this species is involved primarily in the processing of visual signals. How melatonin interacts with circannual rhythms of growth and reproduction is unclear, although a direct interaction between melatonin and the hypothalamopituitary axis is not clearly indicated. J. Comp. Neurol. 409:313–324, 1999.

Comparative performance of growth, biochemical composition and endocrine profiles in diploid and triploid tilapia Oreochromis niloticus L.

Abstract Growth, biochemical composition and endocrine profiles of normal diploid and pressure, heat and cold shock induced triploids of Oreochromis niloticus were investigated. Triploid females were not significantly different from diploid females in growth rate or proximate composition but they were found to be functionally and endocrinologically sterile. Triploid and diploid males showed no significant differences in growth, proximate composition, endocrine profiles or secondary sexual characteristics but the triploids were gametically sterile. The potential value of triploid tilapia being used to avoid precocious sexual maturation and concomitant culture problems are discussed.

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.

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.