Histological changes in the gonad, skin, intestine and olfactory epithelium of artificially‐matured male American eels, Anguilla rostrata (LeSueur)

Abstract

Migratory (silver) male American eels were injected weekly for 5 weeks with human chorionic gonadotropin (hCG), salmon pituitary extract, hydrocortisone 21 -hemisuccinate (cortisol), or saline to determine the effects of induced maturation on the histology of their gonads, skin, intestines and olfactory epithelia. Treatment with hCG induced full sexual maturity, salmon pituitary evoked only limited spermatogenesis, and neither hydrocortisone nor saline had any effect on the gonad. Eels injected with hCG and salmon pituitary experienced no changes in skin morphology, but the epidermal thickness of saline-and hydrocortisone-treated fish decreased. Intestinal morphology did not change in any of the treatment groups. Both the presumed sensory and non-sensory portions of the olfactory epithelium of hCG-and pituitary-treated males exhibited a decrease in thickness, structural degeneration, and non-significant reductions in mucous cell density. Some of these changes in maturing male eels are similar to those previously observed in maturing females but others are different; it appears likely that maturing Anguillu are sexually dimorphic and that these changes are adaptive and not artifacts of the hormone treatments.

Induced spawning and early ontogeny of New Zealand freshwater eels{Anguilla dieffenbachiiandA. australis)

“…The first successful results using exogenous hormone treatments in eels date from the 1930s, when male European eels (Anguilla anguilla) were injected with urine from pregnant women (e.g., Fontaine 1936). Similar experiments with female eels, treated repeatedly with human chorionic gonadotropin (hCG), did not result in significant ovarian development (Bruun et al 1949;Sorensen & Pankhurst 1988). Instead, repeated injections of teleost pituitary suspensions, first successfully applied by Fontaine et al (1964), are now routinely used for induction of vitellogenesis in female eels.…”

Thermal preferenda and behavior of Atlantic eels (genus Anguilla) in relation to their spawning migration

“…Artificial maturation of silver eels produces further metamorphosis that is related to adaptation to the oceanic environment, including increase in eye size, changes in skin pigmentation and structure, retinal organization, structure of skeletal muscle and degeneration of the intestine and olfactory epithelium (Boetius & Boetius 1967, Pankhurst 1982, Pankhurst & Lythgoe 1983, Sorensen & Pankhurst, 1988. Behavioral studies of artificially matured eels have provided insight on possible spawning mechanisms and behavior (Boetius & Boetius 1980, Sorensen & Winn 1984.…”

Deep sequencing of the olfactory epithelium reveals specific chemosensory receptors are expressed at sexual maturity in the European eel Anguilla anguilla

“…). Furthermore, morphological changes in the olfactory epithelium (OE) occur at sexual maturation (Pankhurst & Lythgoe ; Sorensen & Pankhurst ) suggesting that the functional demands on the olfactory system are life stage dependent. It is not yet known if eels use specific olfactory receptor genes or GPCR signal transduction genes at different points in their life cycle to allow them to adapt to differences in environment and to different life stage requirements.…”