Puberty in an early-maturing flatfish, the yellowtail flounder, Limanda ferruginea Storer

Manning, Anthony J. (2003) Puberty in an early-maturing flatfish, the yellowtail flounder, Limanda ferruginea Storer. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (21MB)

Abstract

A description of puberty at the gonadal level, and investigations into its regulation and manipulation were undertaken in order to examine the maturation processes of the yellowtail flounder under culture conditions. Puberty in males occurred after one year of age. Male puberty was noted by the detection of plasma androgens during a novel testicular growth phase in which mitosis and meiosis were concurrent. Female pubertal age was plastic; maturation occurred in 1 +, 2+ and rarely 3+ animals. Culture conditions promoting 0+ growth encouraged puberty in 1 + females. Immature ovaries in primary growth stages were steroidogenic and responsive to in vitro gonadotropic stimulation. The onset of puberty was detected by a plasma 17β-estradiol peak in cortical alveolar stage females prior to vitellogenin incorporation. Mature gametes were produced within a year of the initiation of puberty in both sexes. Females became superior in body size when males underwent testicular maturation; an effect of elevated androgens on male growth was suggested. -- Hormones with reputed dual roles in growth and reproduction were administered long-term in immature females and mature males. Treatment with a gonadotropin-releasing hormone analogue (GnRH-a) failed to advance puberty in females but synchronized the onset of puberty among treated subjects relative to controls. GnRH-a did not accelerate testicular recrudescence and had no effect on growth. High levels of testosterone, whether alone or in combination with GnRH-a, suppressed growth and early gametogenesis in both sexes. A recombinant bovine growth hormone (rbGH) formulation (Posilac®) stimulated growth in males and females, reducing sex differences in body size. A positive rbGH effect on testicular mass was attributed to enhanced body size. Growth stimulation by rbGH delayed the onset of puberty in some females, presumably due to an increased utilization of energy reserves. -- Inducing triploidy was examined as a maturation deterrent. A ten minute hydrostatic pressure treatment of 7 000 psi, initiated five minutes post-sperm activation (7-12°C), is recommended to induce high percentages (92-100%) of triploid larvae. Premetamorphic growth of triploid larvae was inferior to that of diploid larvae. Later, 2+ triploid females exceeded growth rates of maturing 1+ diploid females. Triploidy minimized gonadal development but did not prevent the production of gametes in either sex. -- Yellowtail flounder demonstrated a propensity for early sexual maturation under culture conditions. Management of dietary fat levels, the therapeutic use of rbGH, and the production of triploids are proposed as measures which, alone or in combination, may help to suppress puberty in this pleuronectid flatfish.

Actions (login required)

View Item