RESUMO
Abstract: Leucism is an anomaly recorded in fish species as well as in many other groups of animals in natural environments. An individual with leucism is characterized by the loss of brown or black pigmentation over most of the body. Here, we recorded this condition for an individual of marbled swamp eel Synbranchus marmoratus (Synbranchiformes: Synbranchidae) captured in the Furnas megareservoir, Grande River basin, in Minas Gerais state, southeastern Brazil. The individual had a general color of the body with shades ranging from pale to intense yellowish, but the eyes were black. We also present a discussion on the influence of leucism on the survival of the individual in this study.
Resumo: Leucismo é uma anomalia registrada em espécies de peixes assim como em muitos outros grupos de animais em ambientes naturais. Um indivíduo com leucismo é caracterizado pela perda de pigmentação marrom ou preta na maior parte do corpo. Neste trabalho, nós registramos essa condição para um indivíduo de muçum Synbranchus marmoratus (Synbranchiformes: Synbranchidae) capturado no megareservatório de Furnas, bacia do Rio Grande, no estado de Minas Gerais, sudeste brasileiro. O indivíduo apresentava coloração geral do corpo com tonalidades que variavam do amarelado pálido ao intenso, mas os olhos eram pretos. Nós também apresentamos uma discussão sobre a influência do leucismo na sobrevivência do indivíduo deste estudo.
RESUMO
Sexual differentiation and primary and secondary sexual characteristics in male crustaceans are modulated by hormones produced in the androgenic gland (AG). The AG is also responsible for the determination of morphotypes in caridean shrimps, such as Macrobrachium amazonicum that shows four morphotypes: translucent claw (TC), cinnamon claw (CC), green claw 1 (GC1) and green claw 2 (GC2). Here, we verified the anatomical, histological and ultrastructural characteristics of the AG in different morphotypes of this species with both amphidromous and hololimnetic life cycles. In submissive morphotypes (TC and CC), the AGs are reduced and concentrated in the terminal expansion of the distal portion of vasa deferentia (DVD), the ejaculatory ducts (ED). In dominant morphotypes (GC1 and GC2) these glands lie along the DVD and ED. Two morphological stages (I and II) were recorded for AG cells. In submissive morphotypes stage I cells predominated in the AGs, while in dominant morphotypes stage II cells were more common. AG cells in both stages were positive for proteins, confirming the protein nature of the secreted hormone. Stage I cells have abundant rough endoplasmic reticulum (RER) with numerous parallel cisternae, whereas in stage II cells, the cisternae of RER are highly dilated. Stage II cells do not produce secretory granules, but they undergo hypertrophy and the hormone release to hemolymph probably occurs by holocrine secretion. The AGs in TC, GC1 and GC2 morphotypes increase as the animals grow and are larger in GC1 males. On the other hand, AGs decrease in the CC morphotype as the animal grows. These differences are related to the type of reproductive strategy adopted by each morphotype. In M. amazonicum, the AGs show the same morphological, histochemical and ultrastructural patterns between the different life history populations.