Induction of gonadal maturation at different temperatures in burbot Lota lota.

A rearing experiment was conducted to test whether temperature protocols that differed from a simulation of natural conditions might induce maturation after isothermal grow-out in burbot Lota lota. Lota lota were acclimated to two different temperature regimes: low temperature (LT), close to natural temperature at 4·0° C and elevated, high temperature (HT) at 8·5° C over 40 and 27 days respectively, with all fish then wintered for 47 days. Every second fish was treated with a gonadotropin-releasing hormone analogue. Maturational competence of oocytes was assessed with a germinal vesicle breakdown assay using a novel staining strategy. In both treatments, puberty and maturational progress occurred, characterised by an elevated gonado-somatic index and advanced gonadal stages (histological analysis). Progress of gonadal maturation was reflected by elevated plasma concentrations of testosterone and 11-ketosterone in males and 17ß-oestradiol in females. Ovulation was not observed. Sperm could be activated equally across treatments. In general, LT was more effective than HT treatment, indicated by advanced gonadal stages, higher numbers of oocytes undergoing germinal vesicle breakdown in vitro and elevated sex steroid levels. Hormone treatment could improve effectiveness at HT. In conclusion, less drastic temperature regimes as previously reported in combination with hormone treatments seem sufficient to induce maturation in L. lota after isothermal grow-out.

Influence of temperature on puberty and maturation of pikeperch, Sander lucioperca.

Among external factors, temperature is known to exhibit a prominent role in reproduction of temperate fish species. Here, temperature related induction of puberty in pikeperch Sander lucioperca was investigated. For the first time the key factors of the pikeperch brain-pituitary-gonad axis, targeting the mRNA expression of the luteinising hormone (LH) and the follicle stimulating hormone (FSH), as well as the plasma sex steroids estradiol (E2), testosterone (T), 11-ketotestosteron (11-KT) and 17α,20ß-dihydroxy-4-pregnen-3-one (17,20ß-P) were addressed in the experiment. Concomitant the maturational stages were described histologically. After 3 months, female pikeperch kept at 12°C revealed significant increases in the GSI and plasma E2 concentration and 90% of the females were mid-vitellogenic. After 5 months, females kept between 9 and 15°C exhibited significant up-regulation of E2 and GSI as well as comparable histological outcome. At 6 and 23°C in nearly all females stagnation of oogenesis was recorded. Congruently, T was increased at 12 and 15°C. Expression analysis revealed a significant up-regulation of LHß and FSHß mRNA in females from early-vitellogenesis, and from mid-spermatogenesis in males, correlated to elevated plasma concentrations of steroids (except for E2 in males). In conclusion, moderate temperatures (12-15°C for) for at least 3 months were required to proceed with first maturation in juvenile pikeperch. The most efficient effect was observed at 12°C, while high (23°C) or low (6°C) temperatures prevented gonadal maturation. So temperature was identified as a prime factor in the induction of puberty in pikeperch, as revealed by histological as well as endocrine parameters.