Long-term starvation in the European eel: general effects and responses of pituitary growth hormone-(GH) and somatolactin-(SL) secreting cells

European eels reaching the silver stage stop feeding in freshwater and during their spawning migration to the Sargasso sea (6000 km at least in the Ocean). The total duration of this exceptional fast is not well known. Few data are available on the general condition and the endocrine responses to starvation of migrating eels. In this study male (silver) and female (yellow and silver) eels were kept in freshwater without food for various lengths of time. Animals were killed after 7 months to 3 or 4 years. After a gradual decrease, the final body weight was reduced by 84% in males (52 months) and 67–69% in females (up to 4 years). The condition factor (K) followed a parallel curve. In the pituitary gland, GH cells were hypertrophied and highly stimulated. Their cross-sectional area was negatively correlated to K. Large GH cells remained well immunostained with an anti-eel GH serum after 7 to 12 months of starvation. In the leanest eels, the immunostaining was often reduced and many GH cells appeared degranulated, suggesting a low hormonal storage. In contrast, SL cells were reduced in size and number in the anterior half of the neurointermediate lobe (NIL), but showed a more heterogeneous picture in the caudal portion. GH and SL cell activities seemed to be negatively correlated in starved fish and controlled by different mechanisms. GH appears to play a major role in the long-term survival of fasted eels; SL does not seem to be involved.