Bioaccumulation of mercury, cadmium, zinc, chromium, and lead in muscle, liver, and spleen tissues of a large commercially valuable catfish species from Brazil.

The increasing amounts of heavy metals entering aquatic environments can result in high accumulation levels of these contaminants in fish and their consumers, which pose a serious risk to ecosystems and human health. We investigated the concentrations of mercury (Hg), cadmium (Cd), zinc (Zn), chromium (Cr), and lead (Pb) in muscle, liver, and spleen tissues of Pseudoplatystoma corruscans specimens collected from two sites on the Paraopeba River, Brazil. The level of heavy metals concentrations in the tissues was often higher in viscera (i.e. liver and spleen) than in muscle, and thus, the viscera should not be considered for human consumption. Correlations between metal concentrations and fish size were not significant. Although the levels of muscle bioaccumulation of Hg, Cd, Zn, Cr, and Pb, generally do not exceed the safe levels for human consumption, the constant presence of heavy metals in concentrations near those limits considered safe for human consumption, is a reason for concern, and populations who constantly consume fish from polluted rivers should be warned. Our findings also indicate that in a river network where certain areas are connected to other areas with high rates of environmental pollutants, people should be cautious about the regular consumption of fish, even when the fish consumed are caught in stretches of the basin where contamination levels are considered low, since many of the freshwater fish with high commercial value, such as the catfish surubim, are migratory.

Morphological characteristics of the digestive tract of Schizodon knerii (Steindachner, 1875), (Characiformes: Anostomidae): An anatomical, histological and histochemical study.

The digestive tracts of 44 specimens of Schizodon knerii were studied using anatomical, histological and histochemical techniques. The mouth has terminal position, the lip epithelium is squamous stratified with mucous, claviform cells and taste buds, teeth have an incisive form and the tongue has a stratified squamous epithelium with mucous cells and taste buds. The oropharynx cavity is formed by gill apparatus and pharyngeal teeth. The oesophagus presented pleated mucosa, a stratified squamous epithelium with mucous cells, oesophageal glands and taste buds. The stomach presented cardiac, fundic and pyloric regions, simple prismatic epithelium with tubular glands, with none in the pyloric region. The intestine contains 11-15 pyloric caeca, a simple prismatic epithelium with brush border, goblet cells and lymphocytes. Mucosal cells, oesophageal glands and goblet cells reacted positively to PAS, amylase + PAS, Ab pH 2.5 and Ab pH 0.5. Gastric prismatic cells reacted positively to PAS, amylase + PAS, but only those in the pyloric region reacted positively to Ab pH 2.5 and Ab pH 0.5. The results improve the understanding of the anatomy of S. knerii feeding habits and the presence of mucosubstances in the epithelium, highlights the importance of glycoproteins for passing food through the digestive tract.

Reproductive biology of the characid dourado Salminus franciscanus from the São Francisco River, Brasil.

The neotropical characid Salminus franciscanus is an economically valuable migratory fish whose populations have been drastically reduced in recent decades due to industrial and economic development in Brasil. To study its reproduction, a total of 283 adult specimens were captured in the Upper São Francisco River, downstream from the Três Marias dam, Minas Gerais, south-eastern Brasil, from August 2009 to July 2010. The gonadal maturity stages were determined from histological features of the gonads and gonadosomatic index (GSI). Gametogenesis was assessed by light and electron microscopy. For analysis of the oocyte's surface and fecundity, mature females were subjected to hormonal induction and oocyte stripping. Fish in resting (Stage 1) were common in all samplings, ripening/ripe and spawning (Stages 2 and 3) were predominant in October-November and December-January and post-spawning (Stage 4) occurred from December-January extending until April-May. The GSI followed the morphological changes of gonadal maturation, with a peak in October-November, when maximum GSI (7.08 in females and 3.46 in males) was achieved. From scanning electron microscopy, stripped oocytes showed a funnel-shaped micropyle and a simple oocyte surface arrangement, which is typical for non-adhesive eggs. Fecundity ranged from 160 to 440×10(3) oocytes per female and 129 to 175×10(3)oocytes/kg. The results of this study indicate that S. franciscanus reproduces in the Upper São Francisco River from October to January, exhibiting a total spawning pattern, non-adhesive eggs and high fecundity, providing support for aquaculture and conservation biology of this important neotropical characid fish.

Assessment of spermatogenesis and plasma sex steroids in a seasonal breeding teleost: a comparative study in an area of influence of a tributary, downstream from a hydroelectric power dam, Brazil.

River damming and building of hydroelectric power plants interrupt the reproductive migration routes and change the major physicochemical parameters of water quality, with drastic consequences for populations of migratory fishes. The goal of this study was to evaluate proliferation and cell death during spermatogenesis and serum profiles of sex steroids in Prochilodus argenteus, from the São Francisco River, downstream from the Três Marias Dam. A total of 257 adult males were caught quarterly during a reproductive cycle in two sites: the first 34 km of the river after the dam (site 1) and the second 34-54 km after the dam (site 2), after the confluence with a tributary, the Abaeté River. Seasonal changes in the testicular activity associated with morphometric analyses of germ cells as well as proliferation and testicular apoptosis support a more active spermatogenesis in fish from site 2, where higher levels of sex steroids and gonadosomatic index (GSI) were also found. In site 1, fish presented low serum levels of testosterone, 17ß-estradiol and 17α-hydroxyprogesterone and a low GSI during gonadal maturation. Spermatogonial proliferation (PCNA) and apoptosis (TUNEL) were more elevated in fish from site 1, but spermatocytes were mainly labelled in fish from site 2. Overall, these data demonstrate changes in testicular activity and plasma sex steroids in a neotropical teleost fish living downstream from a hydroelectric dam, supplying new data on fish reproduction in regulated rivers. Moreover, morphometric analyses associated with sex steroids profiles provide reliable tools to assess fish spermatogenesis under environmental stress conditions.

Influence of water temperature on induced reproduction by hypophysation, sex steroids concentrations and final oocyte maturation of the "curimatã-pacu" Prochilodus argenteus (Pisces: Prochilodontidae).

Most fishes with commercial importance from the São Francisco basin are migratory and do not complete the reproductive cycle in lentic environments, such as hydroelectric plant reservoirs, hence natural stocks are declining and there is an urgent need to reduce the pressure of fishing on those wild populations. Therefore, studies on reproductive biology and its relationship with endocrine and environmental factors are key to improving the cultivation techniques of Brazilian fish species. This study examined the influence of water temperature on sex steroid concentrations (testosterone, 17ß-estradiol and 17α-hydroxyprogesterone), spawning efficiency, fecundity, fertilisation rate, larval abnormality rates and involvement of the cytoskeleton during the final oocyte maturation of Prochilodus argenteus under experimental conditions. The results of our study showed that in captivity, sex steroid plasma concentrations and spawning performance of P. argenteus were clearly different for fish kept in water with different temperature regimes. In lower water temperature (23°C), it was observed that: 33% of females did not ovulate, fecundity was lower and vitellogenic oocytes after the spawning induction procedure exhibited a smaller diameter. Moreover, concentrations of 17ß-estradiol and 17α-hydroxyprogesterone were lower and there was a delay in the final oocyte maturation and, consequently, ovulation and spawning. Our experiments showed direct influence of water temperature in the process of induced spawning of P. argenteus. Changes in water temperature also suggest the tubulin involvement in the nuclear dislocation process and the possible action of actin filaments in the release of polar bodies during final oocyte maturation of P. argenteus.

Profiles of sex steroids, fecundity, and spawning of the curimatã-pacu Prochilodus argenteus in the São Francisco River, downstream from the Três Marias Dam, Southeastern Brazil.

The present study evaluated for the first time sex steroid profiles and fecundity in females of Prochilodus argenteus from two sections of the São Francisco River Brazil, downstream from the Três Marias Dam, which influences characteristics of their water habitat. The model species in the study, P. argenteus, is an important commercial and recreational species in Brazil. In the region closest to the dam (section 1), females did not reach final oocyte maturation, failed to spawn, and displayed lesser circulating concentrations of testosterone, 17(-hydroxyprogesterone (17(-P) and 17beta-estradiol (E2) than those farther downstream of the dam (section 2). The endocrine and fecundity deficiencies probably are attributed to lower water temperature and oxygen concentration in (section 1). The follicular atresia rate in the region closest to the dam (26%) was greater than those fish captured farther downstream of the dam (13%), after the Abaeté River (section 2). Variations in testosterone, E2 and 17(-P concentrations in section 2, followed gonadal maturation which are typical features of species which have seasonal reproduction, group-synchronous oocyte development, and are single batch spawners such as P. argenteus. Results document the first evidence of endocrine and reproductive dysfunctions caused by inadequate water conditions in a wild population of the migratory species P. argenteus in the São Francisco River, downstream from the Três Marias dam.

Dual roles for autophagy during follicular atresia in fish ovary.

Autophagy, a highly conserved catabolic program for degrading proteins and organelles, is essential for cell and tissue homeostasis. Primarily, this process has a cytoprotective role under nutrient deprivation, but several stress stimuli can induce autophagy and, thus, distinct programmed cell death (PCD) pathways can be actived when stress is not abolished. Fish ovaries are a suitable experimental model system for studying the mechanisms of PCD due to the presence of postovulatory and atretic (i.e., nonovulated) follicles, which follow different routes after spawning. Apoptosis of the follicular cells is the major mechanism responsible for the rapid resorption of the postovulatory follicles. Recently, we investigated the contribution of PCD during follicular atresia in two species of freshwater fish. In contrast to mammals, this study revealed that follicular apoptosis is not a major process for deletion of follicular cells in atretic follicles. Furthermore, we detected autophagic vacuoles containing degenerating organelles increasing through follicular atresia in both species. In this addendum, we propose a hypothesis for follicular cell removal during ovarian regression in oviparous fish. In this model, autophagy could have dual roles in follicular atresia. Thus, fish ovaries after breeding are suitable models for studying the interactions among the different cell death pathways.