Heavy metal contamination in a highly consumed Brazilian fish: immunohistochemical and histopathological assessments.

Due to industrial, rural, and domestic waste disposal, heavy metals such as cadmium (Cd), chromium (Cr), lead (Pb), zinc (Zn), copper (Cu), and iron (Fe) continually infiltrate aquatic environments. These pollutants do not degrade naturally and, thus, have a high capacity for bioaccumulation in tissues and organs. The present study uses histological and immunohistochemical analyses to evaluate the contamination status of Salminus franciscanus, a large and economically important fish. Levels of Cd, Cr, Pb, Zn, Cu, and Fe were evaluated by atomic absorption spectrometry in the liver and muscle of fish sampled from two tributaries of the upper São Francisco River Basin, Brazil: the Abaeté and Paraopeba Rivers. In addition, histopathological alterations and expressions of three environmental biomarkers were assessed: metallothionein (MT), heat shock protein-70 (HSP70), and cytochrome P450-1A (CYP1A). The results show that fish from the Paraopeba River are unsuitable for human consumption, with several metals being detected above the safe limits established by the World Health Organization. Histopathological alterations in the liver and spleen were also significantly more frequent in fish from the Paraopeba River than in those from the Abaeté River (P < 0.05). Significant differences in the expressions of environmental biomarkers were observed between the rivers. Fish from the Abaeté River presented significantly higher values of the gonadosomatic index (GSI) and lower levels of metal contamination in the liver and muscle.

Reproductive variables of Brycon nattereri Günther, 1864 (Pisces: Characidae), an endangered commercial species.

In Brazil, fishing in continental waters is prohibited from November to February, the rainy season, when most commercially important fish species are reproductively active. Brycon nattereri is a native species to the Paraná, Tocantins, and São Francisco River basins in Brazil and is on the national list of species threatened with extinction. The goal of this study was to analyse the main reproductive variables of B. nattereri from the Lourenço Velho River, located in the Paraná River basin, south-eastern Brazil. From 2013-2016, 326 specimens (156 females and 170 males) were caught bimonthly using gill nets. Biometric data, gonadosomatic index (GSI), and fecundity were determined for each specimen. The gonadal maturation stages and the breeding season were established. There were relatively greater GSI values for males and average values were similar to those of females, an uncommon feature in Neotropical freshwater fish. The greatest frequencies of mature fish occurred from April to July in the dry season, which is when there are least ambient temperatures. The fecundity for body weight varied from 16,300 to 62,800 oocytes per female and fully developed vitellogenic oocytes had a mean diameter of 1175 ± 278.87 µm. These results indicate that B. nattereri breeds in the dry season when the water temperature is colder and, therefore, protection from fishing of this species during this season needs to be established.

Heavy Metals and Histopathological Alterations in Salminus franciscanus (Lima & Britski, 2007) (Pisces: Characiformes) in the Paraopeba River, Minas Gerais, Brazil.

Cu, Pb, Cd, Zn, Cr, Hg, and Fe in the liver, spleen and muscle, of the fish Salminus franciscanus, from two sections of Paraopeba River, highly affected by anthropogenic influences, was detected in levels above those recommended for human consumption. Positive correlations between fish size and levels of metals were detected for Cd, Pb, Hg, and Zn. In the livers, areas with lipid accumulation and pigmented macrophages were also observed, as was fibrosis of the spleen in the parenchymal area through the presence of pigmented macrophages. The diameter of vitellogenic follicles was less and the frequency of atresia was higher in fish from section A. Thus, our study showed that beyond the risk to the population that eats S. franciscanus from the Paraopeba River, we should also consider the risk to the conservation of this species, since histopathological changes were detected in target organs and in some reproductive parameters.

Early larvae ontogeny of the Neotropical fishes: Prochilodus costatus and P. argenteus (Characiformes: Prochilodontidae).

Early development of fish larvae is a highly dynamic process and its study may provide important information about ontogenetic development, bioenergetic growth, behaviour, taxonomic characteristics for identification in natural environments, identification of spawning areas, and population monitoring. With the aim to provide knowledge about their growth and behaviour, to support larval rearing, and also taxonomic purposes, we studied the life history of the Prochilodus argenteus and P. costatus from hatching until the complete absorption of the yolk. Larvae were obtained through artificial reproduction at the Hydrobiology and Aquaculture Station of Três Marias, Minas Gerais, Brazil. Immediately after hatching, 100 larvae of each species were put in two plastic incubators for conditioning. On a daily basis, larvae behavior was recorded and 14 larvae of each species were collected to analyse body morphology. On the first day after hatching, larvae of P. costatus and P. argenteus showed an elongated and transparent body; the yolk sac was filled with individualized yolk globules. In both species, the embryonic fin rounded the caudal region of the body, the retina was non-pigmented and the gut was obliterated. At the second day post-hatching, larvae of both species dendritic chromatophores had emerged, the mouth was obliterated and the pectoral fin was observed. The larvae showed 38-43 myomeres in P. costatus and 42-43 in P. argenteus. For both species, the gas bladder was inflated and the lumen of the gut was already open. On the third day post-hatching, the mouth of P. costatus and P. argenteus was already open in a sub-terminal position; the retina was pigmented; the gill arches had lamellar protrusions and were partially covered by the operculum. On the fourth day post-hatching, the pigmentation pattern was maintained with greater intensity; the mouth occupied a terminal position, the yolk sac was almost completely reabsorbed, and the pectoral and caudal fins showed mesenchymal rays in both species. The gut showed a broad lumen with folded mucosa and epithelium with striated border. The larvae of both species showed similar swimming behaviour. Our study provided understanding about the morphophysiological aspects, species identification, larval development and growth, and the ontogenic characteristics of two Neotropical fishes with importance for commercial and sports fishing.

Induced spawning and reproductive variables of the catfish Lophiosilurus alexandri Steindachner, 1876 (siluriformes: pseudopimelodidae)

Lophiosilurus alexandri is an endemic fish from the São Francisco River basin, Brazil. The aim of this study was to induce L. alexandri to spawn and to obtain data on several reproductive variables for this species. For induced spawning, adults were submitted to Cyprinus carpio pituitary homogenate (CPH). Nine of the 12 females (75%) responded positively to the treatment. The stripping of oocytes was performed 8.4 h after the second dose of CPH with the water temperature maintained at 26ºC. The number of stripped oocytes per gram of ova was 74 ± 5 oocytes g-1, and the mean oocyte diameter was 3.1 ± 0.2 and 3.6 ± 0.2 mm, before and after hydration, respectively. The oocytes were opaque, yellowish, demersal, highly adhesive, and covered by a gelatinous coat. The total fecundity was 4,534 ± 671 oocytes, and the fertilization rate was 59%. The initial and final fertilities were 2,631 ± 740 and 1,542 ± 416 embryos, respectively. Larval hatching occurred up to 56 h after fertilization, and the larvae had a total length of 8.4 ± 0.1 mm. This work provides important biological information for L. alexandri that can be used for management and conservation of this species.

Lophiosilurus alexandri é um peixe endêmico da bacia do rio São Francisco, Brasil. O objetivo do trabalho foi induzir L. alexandri à desova e obter dados sobre várias variáveis reprodutivas para esta espécie. Para desova induzida, adultos foram submetidos ao homogeneizado de hipófise de Cyprinus carpio (HHC). Nove das 12 fêmeas (75%) responderam positivamente ao tratamento. A extrusão dos ovócitos aconteceu 8,4 h após a segunda dose de HHC com a temperatura da água mantida a 26ºC. O número de ovócitos liberados por grama de ova foi de 74 ± 5 ovócitos g-1 e a média do diâmetro ovocitário foi de 3,1 ± 0,2 e 3,6 ± 0,2 mm, antes e depois da hidratação, respectivamente. Os ovócitos foram opacos, amarelo-castanho, demersais, altamente adesivos e revestidos por capa gelatinosa. A fecundidade total apresentou 4.534 ± 671 ovócitos e a taxa de fertilização foi de 59%. As fertilidades inicial e final foram de 2.631 ± 740 e 1.542 ± 416 embriões, respectivamente. A eclosão das larvas aconteceu até 56 h após a fertilização e as larvas tiveram comprimento total de 8,4 ± 0,1 mm. Este trabalho fornece informações biológicas importantes para L. alexandri, que podem ser utilizadas para o manejo e conservação desta espécie.

Oocyte adhesiveness and embryonic development of Astyanax bimaculatus (Linnaeus, 1758) (Pisces: Characidae).

This study shows for the first time the presence of a jelly coat on oocytes of neotropical Characiformes fish. This structure could be responsible for the adhesiveness of Astyanax bimaculatus oocytes, a species widely distributed in South America including in the São Francisco River basin in Brazil. Adult specimens of A. bimaculatus were submitted to artificial reproduction in order to analyse the egg morphology and embryonic development. The eggs were fertilised and kept in incubators with a water temperature of 24°C so that embryogenesis could be monitored. Ovulated and unfertilised oocytes were also collected and submitted to routine histological techniques. Astyanax bimaculatus oocytes were found to be spherical, yellowish, and covered by a thin jelly coat with a slightly adhesive surface. The mean oocyte diameter was 1.03 ± 0.03 mm, the perivitelline space was 0.21 ± 0.02 mm and the jelly coat's thickness was 0.04 ± 0.01 mm. Positive periodic acid-Schiff (PAS) stain and Alcian blue stain pH 2.5 indicated the presence of neutral glycoproteins, and carboxylated acid glycoconjugates on the jelly coat that formed mucosubstances that may be associated with egg adhesiveness. At a water temperature of 24°C, blastopore closure and hatching occurred at 5 h and 17 h after fertilisation, respectively. The results of this study provide essential information for phylogenetic studies and for a better understanding of the reproductive strategy of A. bimaculatus, currently included in the incertae sedis group of the Characidae family due to the lack of monophyly among the families of the group.

Comparative morphology of the gonadal structure related to reproductive strategies in six species of neotropical catfishes (Teleostei: Siluriformes).

We studied the relationship between the morphology of the reproductive system and the reproductive strategies of six neotropical catfishes using macroscopic and microscopic analyses. The reproductive system of the examined Siluriformes showed diversified characteristics, but permitted their being grouped according to three reproductive strategies: pelagic spawning, demersal spawning, and internally fertilizing. The pelagic spawners Pseudoplatystoma corruscans and Conorhynchos conirostris have testes that are characterized by filiform lobes, absence of testicular secretion, full-grown oocytes of small diameter, thin zona radiata, and cuboidal follicular cells. Pimelodus maculatus is morphologically distinct from the other two pelagic spawners catfishes due to the presence of testicular secretion. The demersal spawners Lophiosilurus alexandri and Rhinelepis aspera possess homogeneous testicular secretion, large mature oocytes, and columnar follicular cells. The most specialized reproductive system was observed in the internally fertilizing Trachelyopterus galeatus, which possesses a seminal vesicle accessory to the testes, spermatozoa with elongated nuclei that form spermatozeugmata, and a secretory ovarian lamellar epithelium that is associated with sperm storage. The reproductive system observed in Neotropical catfishes showed a relationship associated with the type of fertilization and the reproductive strategies of the six species studied.