First Observation of a Spontaneously Matured Female European Eel (Anguilla anguilla).

This study reports on the first observation of a spontaneously matured female European eel. The 43-year-old eel, together with eleven other females, resided at an aquarium house since their capture in 2002 and stocking as glass eels in 1978. In June 2019, the girth of the belly of the female increased as a sign of oocyte maturation. The specimen had an estimated gonadosomatic index (GSI) of 47, only half of the oocytes were hydrated and matured, indicating that European eels are polycyclic batch spawners. The live eels of the cohort were still in the previtellogenic phase but their eye sizes were close to that of the matured eel. We hypothesize that substances released by other maturing and spawning fishes may have triggered puberty of the eel. This first observation, and the possibility of more eels maturing in the near future, provides a natural reference for the sexual maturation of the European eel.

Signaling between the pituitary gland and the testes: inverse relationship between serum FSH and inhibin B concentrations in boys in early puberty.

OBJECTIVES: To study the relationship between serum inhibin B and sex steroid concentrations and pituitary FSH responsiveness to GnRH in boys in early puberty, and to examine serum inhibin B levels in prepubertal boys with different timing of the onset of gonadotropin deficiency (GD). DESIGN: Twenty-five boys with constitutional delay of puberty (CDP; 20 in Tanner stage G2 and 5 in G3; age range, 13. 5-16.8 years) and eight prepubertal boys (G1P1) with GD (age range, 10.0-13.2 years) were clinically examined, and serum inhibin B, testosterone and estradiol concentrations were measured from sera obtained immediately before the administration of GnRH (Relefact; 3.5 microgram/kg, maximum 100 microgram i.v.). Thereafter, FSH levels were measured at 30min intervals up to 90min. RESULTS: In the boys with CDP, basal inhibin B and FSH levels did not correlate. However, inhibin B and GnRH-stimulated FSH concentrations (r(S)= -0.43 to -0.45, n=25, P<0.05) and the difference between basal and peak serum FSH levels were inversely related (r(S)= -0.63, n=25, P<0.005). This relationship remained significant in boys at stage G2 (r(S)= -0.66, n=20, P<0.005). Basal testosterone concentrations and GnRH-induced FSH levels did not correlate. Estradiol levels were too low (64% of the boys had estradiol levels below the assay sensitivity) to allow correlation analysis. The boys with GD had low inhibin B concentrations (range, <15.6-53pg/ml); the lowest levels were observed in boys with presumably congenital onset of the disease. Serum inhibin B levels and testis volumes correlated positively (r(S)=0.70, n=8, P=0.07). CONCLUSIONS: These results suggest that, in boys, the reciprocal regulation between inhibin B and FSH is in operation before mid-puberty. Moreover, autonomous inhibin B secretion by the prepubertal human testis is likely to reflect the number of Sertoli cells.