Hoplosternum Littorale Research Articles

Defining the reproductive period of freshwater fish species using the Gonadosomatic Index: a proposed protocol applied to ten species of the Patos Lagoon basin

ABSTRACT This contribution records the reproductive periods of ten dominant freshwater fish species from the Patos Lagoon and Guaíba Lake (Astyanax fasciatus, Cyphocharax voga, Hoplias malabaricus, Oligosarcus jenynsii, Oligosarcus robustus, Hoplosternum littorale, Loricariichthys anus, Parapimelodus nigribarbis, Trachelyopterus lucenai, Pachyurus bonariensis). Data were derived from monthly samples in Casamento Lake (northern Patos Lagoon; Nov. 2002 to Apr. 2004) and Guaíba Lake (Jun. 2005 to May 2006). The reproductive period was determined according to the monthly variation of the gonadosomatic index (GSI). Fish reproduction was identified during all months of the year. Oligosarcus jenynsii started reproduction in winter, but extended spawning to spring (early warming-water reproduction). Three species also presented reproduction during warming water months, but beginning in spring and finishing in summer (late warm-water reproduction): P. nigribarbis, T. lucenai and P. bonariensis. Three species presented relatively short reproduction periods on summer (spotted warm-water reproduction): H. malabaricus, H. littorale and L. anus, and only one species reproduces almost continuously during warmer waters (long-season warm-water reproduction): A. fasciatus. Finally, two other species presented a very distinct reproductive pattern, starting reproduction on late summer but increasing GSI values along autumn and winter (long-season cooling-water reproducers): C. voga and O. robustus.

High waterborne Mg does not attenuate the toxic effects of Fe, Mn, and Ba on Na+ regulation of Amazonian armored catfish tamoatá (Hoplosternum litoralle).

Formation water (FoW) is a by-product from oil and gas production and usually has high concentrations of soluble salts and metals. Calcium (Ca) and magnesium (Mg) have been shown to reduce the toxicity of metals to aquatic animals, and previous study showed that high waterborne Ca exerts mild effect against disturbances on Na+ regulation in Amazonian armored catfish tamoatá (Hoplosternum littorale) acutely exposed to high Fe, Mn, and Ba levels. Here, we hypothesized that high Mg levels might also reduce the toxic effects of these metals on Na+ regulation of tamoatá. The exposure to 5% FoW promoted an increase in Na+ uptake and a rapid accumulation of Na+ in all tissues analyzed (kidney<plasma<gills<carcass<liver), besides increasing the branchial activity of both NKA and v-type H+-ATPase in fish. High waterborne Mg lowered Na+ efflux rates and markedly inhibited Na+ uptake, and also reduced both NKA activity and newly Na+ accumulation in gills of fish. High Fe levels increased Na+ net losses and inhibited Na+ uptake in tamoatá. The diffusive Na+ losses and the newly accumulated Na+ in gills were reduced in fish exposed to high Mn and Ba. High waterborne Ba also inhibited NKA in gills, while both high Mn and Ba inhibited v-type H+-ATPase in kidney of tamoatá. High Mg did not lessen the toxic effect of Fe on Na+ net fluxes, and reduced even more Na+ uptake and the newly Na+ accumulation in gills and plasma, and did not prevent the inhibition of both NKA and v-type H+-ATPases in kidney. Furthermore, Mg did not attenuate the effect of Mn on inhibition Na+ uptake, keeping the activity of v-type H+-ATPase in kidney significantly lowered. High Mg levels mildly attenuated the effects of Ba in Na+ balance by increasing the new accumulation of Na+ in liver, and restore the activity of both NKA and v-type H+-ATPase in gills of tamoatá. Overall, high waterborne Mg does not have a strong contribution to, or have only minor effects, in protecting tamoatá against disruptions in Na+ regulation mediated by high Fe, Mn, and Ba levels.

Patterns of the parasite communities in a fish assemblage of a river in the Brazilian Amazon region.

This paper characterizes the pattern of ectoparasite and endoparasite communities in an assemblage of 35 sympatric fish from different trophic levels in a tributary from the Amazon River system, northern Brazil. In detritivorous, carnivorous, omnivorous and piscivorous hosts, the species richness consisted of 82 ectoparasites and endoparasites, but protozoan ectoparasites such as Ichthyophthirius multifiliis, Piscinoodinium pillulare and Tripartiella sp. were dominant species predominated, such that they were present in 80% of the hosts. The taxon richness was in the following order: Monogenea > Nematoda > Digenea > Crustacea > Protozoa > Acanthocephala = Cestoda > Hirudinea. Among the hosts, the highest number of parasitic associations occurred in Satanoperca jurupari, Aequidens tetramerus, Hoplerythrinus unitaeniatus, Hoplosternum littorale, Cichlasoma amazonarum, Chaetobranchus flavescens, Squaliforma emarginata, Chaetobranchopsis orbicularis and Hoplias malabaricus. A weak positive correlation between ectoparasite abundance and length of the hosts was observed. Ectoparasite communities of detritivorous, carnivorous and omnivorous hosts were similar, but these differed from the communities of piscivorous hosts. Larval endoparasite species with low host specificity were the main determinants of the parasite infracommunity structure of the fish assemblage. Fish assemblage had few species of helminth that were specialist endoparasites, while many were parasites at the larval stage, infecting intermediate and paratenic hosts. Finally, carnivorous and omnivorous hosts harbored endoparasite communities that were more heterogeneous than those of detritivorous and piscivorous hosts. This result lends supports to the notion that the feeding habits of the host species are a significant factor in determining the endoparasites fauna.

Parasitic communities of Hoplosternum littorale (Hancock, 1828) as indicators of environmental impact.

The parasites are indicative of several biological aspects of their hosts, including their diet, migration, recruitment and phylogeny, but they can also be direct indicators of the environmental quality. Hoplosternum littorale is a fish that has a high commercial value in some South American countries. The fishes were collected from January to July 2012, in two locations of the Peixe River in the municipality of Anhembi, State of São Paulo, Brazil, which had different environmental and limnological characteristics (river mouth and Lagoa Cabeça de Boi). An amount of 30 fish specimens were captured in each location for the analysis of their parasitic fauna. Nine species of metazoan parasites were collected. Both Brillouin`s diversity index and Margalef`s richness index were greater in the Lagoa Cabeça de Boi. The ratio of heteroxenous and monoxenous parasite species richness (SH/SM) was higher in the Lagoa Cabeça de Boi. The results of the physicochemical analysis of the water showed that the mouth of the Peixe River can be considered an area that suffers more from anthropogenic actions than the Lagoa da Cabeça de Boi. Proteocephalus sp., Gyrodactylus sp., Scleroductus sp. and Capillaria (Neocapillaria) pterophylli are being registered for the first time in this host.

Remarkable genetic homogeneity supports a single widespread species of Hoplosternum littorale (Siluriformes, Callichthyidae) in South America

Hoplosternum littorale is a widespread, non-migratory, air-breathing armored catfish (Callichthyidae, Siluriformes) present in most river drainages of tropical South America. This species has invaded aquatic habitats out of its native range. The distribution and unity of this species is supported by strong morphological evidences, but only few molecular data are available. As for February 2017, 45 partial mitochondrial gene sequences for H. littorale were deposited at the U.S. National Center for Biotechnology Information (NCBI) GenBank. The nearly complete mitochondrial genomes from two individuals of H. littorale sampled in geographically isolated populations were sequenced and compared to the intraspecific divergence encountered in a related species, Corydoras nattereri. Tamura-Nei corrected distances between the mitochondrial genomes from the two H. littorale was 0.004, equivalent to the distance found among individuals from the same population of C. nattereri (0.002) and considerably smaller than the distance between C. nattereri and C. schwartzi (0.123). An insertion of 30 nucleotides between the ATPase 6 and the COIII genes was identified in H. littorale. This insertion is homologous to the one previously noted in two species of Corydoras. This work supports H. littorale as a single and widespread species of Callichthyidae catfish. The new genetic resources for H. littorale are now available to support further studies with larger sampling sizes.

Effect of thermal stress on metabolic and oxidative stress biomarkers of Hoplosternum littorale (Teleostei, Callichthyidae)

The present study aimed to investigate in Hoplosternum littorale (Hancock, 1828) the effects of different water temperatures (10°C, 25°C-control group- and 33°C) on physiologic and metabolic traits following acute (1day) and chronic (21days) exposures. We analyzed several biomarker responses in order to achieve a comprehensive survey of fish physiology and metabolism under the effect of this natural stressor. We measured morphological indices, biochemical and hematological parameters as well as oxidative stress markers. To evaluate energy consumption, muscle and hepatic total lipid, protein and glycogen concentrations were also quantified. Extreme temperatures exposures clearly resulted in metabolic adjustments, being liver energy reserves and plasma metabolites the most sensitive parameters detecting those changes. We observed reduced hepatosomatic index after acute and chronic exposure to 33°C while glycogen levels decreased at both temperatures and time of exposure tested. Additionally, acute and chronic exposures to 10°C increased liver lipid content and plasma triglycerides. Total protein concentration was higher in liver and lower in plasma after chronic exposures to 10°C and 33°C. Acute exposition at both temperatures caused significant changes in antioxidant enzymes tested in the different tissues without oxidative damage to lipids. Antioxidant defenses in fish failed to protect them when they were exposed for 21days to 10°C, promoting higher lipid peroxidation in liver, kidney and gills. According to multivariate analysis, oxidative stress and metabolic biomarkers clearly differentiated fish exposed chronically to 10°C. Taken together, these results demonstrated that cold exposure was more stressful for H. littorale than heat stress. However, this species could cope with variations in temperature, allowing physiological processes and biochemical reactions to proceed efficiently at different temperatures and times of exposure. Our study showed the ability of H. littorale to resist a wide range of environmental temperatures and contributes for the understanding of how this species is adapted to environments with highly variable physicochemical conditions.

Microplastics ingestion by a common tropical freshwater fishing resource

Microplastics pollution is widespread in marine ecosystems and a major threat to biodiversity. Nevertheless, our knowledge of the impacts of microplastics in freshwater environments and biota is still very limited. The interaction of microplastics with freshwater organisms and the risks associated with the human consumption of organisms that ingested microplastics remain major knowledge gaps. In this study, we assessed the ingestion of microplastics by Hoplosternum littorale, a common freshwater fish heavily consumed by humans in semi-arid regions of South America. We assessed the abundance and diversity of both plastic debris and other food items found in the gut of fishes caught by local fishermen. We observed that 83% of the fish had plastic debris inside the gut, the highest frequency reported for a fish species so far. Most of the plastic debris (88.6%) recovered from the guts of fish were microplastics (<5 mm), fibres being the most frequent type (46.6%). We observed that fish consumed more microplastics at the urbanized sections of the river, and that the ingestion of microplastics was negatively correlated with the diversity of other food items in the gut of individual fish. Nevertheless, microplastics ingestion appears to have a limited impact on H. littorale, and the consequences of human consumption of this fish were not assessed. Our results suggest freshwater biota are vulnerable to microplastics pollution and that urbanization is a major factor contributing to the pollution of freshwater environments with microplastics. We suggest the gut content of fish could be used as a tool for the qualitative assessment of microplastics pollution in freshwater ecosystems. Further research is needed to determine the processes responsible for the high incidence of microplastics ingestion by H. littorale, and to evaluate the risk posed to humans by the consumption of freshwater fish that ingested microplastics.

Exposure to waterborne copper and high temperature induces the formation of reactive oxygen species and causes mortality in the Amazonian fish Hoplosternum littorale

Hoplosternum littorale is an Amazon fish that lives in urban areas surrounded by polluted igarapes, where elevated copper concentrations eventually occur. The central goal of this study was to evaluate the associated effects of high temperature and copper contamination on survival time and biochemical responses of the Amazonian fish species H. littorale. We exposed fish to two nominal dissolved copper concentrations (50 and 500 µg l−1) and combined temperatures of 28 and 34°C. Our findings showed that the combination of these variables affects the survival time of this species. The activity of the biotransformation enzymes ethoxyresorufin-O-deethylase and glutathione-S-transferase showed no alterations in fish within all treatments. The increase of reactive oxygen species and the decrease in potential total antioxidant capacity promoted the imbalance in the antioxidant system. An induction in superoxide dismutase activity occurred in fish exposed to copper concentrations of 50 and 500 µg l−1 at both temperatures, suggesting liver impairments. Thus, we suggest that H. littorale is sensitive to copper, and this sensitivity is increased further with exposure to high temperatures, particularly in the survival time and reactive oxygen species formation of this fish species.

HEAVY METAL DISTRIBUTION IN THE SEDIMENT AND HOPLOSTERNUM LITTORALE FROM MANAUS INDUSTRIAL

We collected sediment samples in Igarape do Quarenta ( IQ40 ) to extraction of heavy metal into five fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter, and residual according to Tessier et al. (1979) . To the sequential extraction procedure in a 50 mL tube added 1 g of sediment sample. To analyze from heavy metal present into muscle and liver from Hoplosternum littorale, we collected twenty species and analyzed h eavy metals in Hoplosternum littorale and sediment sequential fractions by Flame Absorption Atomic Spectrometry ( FAAS ). As a tool alternative statistical analysis, we suggest the use of beanplot in the results obtained by sequential fraction. The results show high heavy concentrations in the exchangeable, bound to carbonates, bound to iron and manganese oxides, bound to organic matter fractions. The beanplot shows being an important tool to understand the behavior of the heavy metal in sequential fractions present in contaminated sediment. High Zn and Cu concentration found exchangeable fraction explain the high concentration in muscle and live from Hoplosternum littorale . doi: https://doi.org/10.18540/2446941602022016070

Facilitation underpinning the success of the non-native catfish Hoplosternum littorale (Callichthyidae) in lakes of the Middle Doce River Basin, southeastern Brazil

Facilitation is defined as an interaction between two or more species, which benefits at least one of them and causes harm to neither. The establishment of non-native species in new areas is a global phenomenon that raises the question of how facilitation may help in successful biological invasions. We describe a possible facilitation process between the catfish Hoplosternum littorale (Tamboatá) and its predators: Pygocentrus nattereri (piranha) and Cichla cf kelberi (tucunaré), all non-native fish that live in the lakes of the Middle Doce River Basin, southeastern Brazil. We found evidence of indirect facilitation, where non-native predators probably release H. littorale from competition, as they prefer to prey on native fish. Our main evidence in favor of this interpretation was a difference in the abundance of H. littorale between lakes where these species co-occur and lakes where H. littorale is the only non-native fish species. This difference was not associated with environmental differences between lakes or spatial segregation of age classes of H. littorale. Differences in peak activity among H. littorale and non-native predators are probably the main driver of co-occurrence.

Philocorydoras longus sp. n. (Monogenea, Dactylogyridae) from the gills of Hoplosternum littorale (Siluriformes, Callichthyidae) in Southeastern Brazil and the reassignment of two species from the genus Urocleidoides to Philocorydoras

Summary Philocorydoras longus sp. n. (Dactylogryridae) is described from the gills of the freshwater fish Hoplosternum littorale (Hancock, 1828) (Callichthyidae) from Jurumirim reservoir, Upper Paranapanema River, São Paulo State, Brazil. This new species belongs to the genus Philocorydoras mainly by possessing a curved cirrus accompanied by an accessory piece attached by a conspicuous filament. Philocorydoras longus sp. n. most resembles P. platensis, but differs by having delicate and smaller hooks, grooves in ventral and dorsal anchors, larger cirrus and accessory piece, and ventral bar with a long postero-medial process. Two species of the genus Urocleidoides (U. corydori Molnar, Hanek et Fernando, 1974 and U. margolisi Molnar, Hanek et Fernando, 1974) originally described from the gills of Corydoras aeneus (Gill, 1858) from Talparo River, Trinidad (near Brazil), were transferred to the genus Philocorydoras mostly by the absence of a sinistral vaginal sclerite (i. e., the primary characters of Urocleidoides) and counterclockwise cirral rings (i.e., curved tube, and tapered anteriorly in Philocorydoras). The new species is the fourth species assigned to the genus and the first recorded for Brazil.

Selected population characteristics of the non-native catfish Hoplosternum littorale (Hancock, 1828) in central Florida, USA

This study reports the length-weight relationship (LWR), Fulton's condition factor ( K ), and sex ratio of the non-native catfish Hoplosternum littorale (Hancock, 1828) in Florida for the first time. Sampling was conducted from November 2013 to April 2014 in Tosohatchee Wildlife Management Area in Christmas, Florida. A total of 477 specimens were caught (6.4-13.5 cm TL). The allometric coefficient b of the LWR was greater than the isometric value ( b =3.11), suggesting positive allometric growth. The average value for Fulton's condition factor ( K ) was 1.396, with no significant differences between juvenile and adult size classes. The results present certain disparities from data recorded from the fishes' native range, suggesting that this freshwater invasive may be flourishing in Florida. In addition, a new maximum total length of the species is reported.

Physiological and metabolic adjustments of Hoplosternum littorale (Teleostei, Callichthyidae) during starvation

All animals face the possibility of limitations in food resources that could ultimately lead to mortality caused by starvation. The primary goal of this study was to characterize the various physiological strategies that allow fish to survive starvation. A multiparametric approach, including morphological biomarkers, blood plasma metabolites, oxidative stress and energy reserves, was used to assess starvation effects on the fish Hoplosternum littorale. Adult specimens were maintained at four experimental groups: control (fed ad libitum), and starved (not fed) fish for 7 and 28 days. Significant changes were observed not only after 28 days, but also after 7 days of starvation. In the shorter period, the hepatosomatic index as well as plasma triglycerides and glucose were significantly lower in starved fish than in the control ones. These results were accompanied by reduced lipid, glycogen and protein reserves in liver and diminished glycogen content in muscle, suggesting the need of these macromolecules as fuel sources. In addition, increased antioxidant enzyme activities were observed in gills, without evidence of oxidative stress in any of the evaluated tissues. Most significant differences were found in 28-days starved fish: total body weight together with the hepatosomatic index was lower when compared to control fish. The plasmatic metabolites tested (glucose, triglyceride, cholesterol and protein), all energy reserves in liver and glycogen content in muscle decreased in 28-days starved fish. Lipid oxidative damage was reported in liver, kidney and brain, and antioxidant enzymes (GST, GR, GPx and CAT) were activated in gills. According to the multivariate analysis, oxidative stress markers and metabolic parameters were key biomarkers that contributed in separating starved from fed fish. Our study allowed an integrated assessment of the fish response to this particular condition.

Microbiological Quality of Three Freshwater Fish Species from Two Local Markets in Region 6, (Corentyne, East Berbice) Guyana

Present case study was carried out during 2013, to assess the microbiological quality of three freshwater fishes (Hoplosternum littorale, Cichlasoma bimaculatum and Hoplias malabaricus) offered for sale at two local markets in region 6. Fishes were examined for microbial quality and compared to the recommended levels of U.S Food and Drug Association (FDA) and Environmental Protection Agency (EPA) for fish and fisheries product. The results revealed based on the statistical test CHI-SQAURE that the microbial levels for the three freshwater fishes deviated significantly from U.S FDA and EPA expected standard. ANOVA done on the results further showed that there was no significant difference in coliform level among fish species and markets and for E. coli level, there was also no significant difference except at p&lt;0.01. In conclusion, the three freshwater fishes offered for sale at local markets were not of acceptable standard based on U.S FDA and EPA Acceptable level and thus implores risk to human health.

Fast-starting after a breath: air-breathing motions are kinematically similar to escape responses in the catfish Hoplosternum littorale.

ABSTRACTFast-starts are brief accelerations commonly observed in fish within the context of predator–prey interactions. In typical C-start escape responses, fish react to a threatening stimulus by bending their body into a C-shape during the first muscle contraction (i.e. stage 1) which provides a sudden acceleration away from the stimulus. Recently, similar C-starts have been recorded in fish aiming at a prey. Little is known about C-starts outside the context of predator–prey interactions, though recent work has shown that escape response can also be induced by high temperature. Here, we test the hypothesis that air-breathing fish may use C-starts in the context of gulping air at the surface. Hoplosternum littorale is an air-breathing freshwater catfish found in South America. Field video observations reveal that their air-breathing behaviour consists of air-gulping at the surface, followed by a fast turn which re-directs the fish towards the bottom. Using high-speed video in the laboratory, we compared the kinematics of the turn immediately following air-gulping performed by H. littorale in normoxia with those of mechanically-triggered C-start escape responses and with routine (i.e. spontaneous) turns. Our results show that air-breathing events overlap considerably with escape responses with a large stage 1 angle in terms of turning rates, distance covered and the relationship between these rates. Therefore, these two behaviours can be considered kinematically comparable, suggesting that air-breathing in this species is followed by escape-like C-start motions, presumably to minimise time at the surface and exposure to avian predators. These findings show that C-starts can occur in a variety of contexts in which fish may need to get away from areas of potential danger.

Karyotypic diversity and chromosome evolution in the armored catfishes Callichthyinae (Siluriformes, Callichthyidae)

The Callichthyinae subfamily is composed of five genera with a small number of described species. Molecular cytogenetics studies show the scarcity of records for this subfamily. The aim of the present study was to employ cytogenetic parameters in the analysis of three species belonging to the subfamily Callichthyinae sampled from the Parana River (Brazil). Callichthys callichthys had 2n = 56 chromosomes (26 m-sm + 30 st-a); Lepthoplosternum pectorale had 2n = 64 chromosomes (8 m-sm + 56 st-a); and Hoplosternum littorale had 2n = 60 chromosomes (8 m-sm + 52 st-a). Regarding the location of the nucleolar organizer regions (NORs) (Ag-staining and 18S rDNA-FISH), different situations were found: single NORs in H. littorale and C. callichthys; multiple NORs in L. pectorale, with intra-individual and inter-individual variation. Heterochromatin was observed in the centromeric region in the chromosomes of the three species. Equilocal, interstitial bands were also found in H. littorale. Physical mapping of 5S ribo...

New host records and a checklist of fishes infected with Austrodiplostomum compactum (Digenea: Diplostomidae) in Brazil

This study reports the infection of fishes by Austrodiplostomum compactum metacercariae in the Chavantes reservoir, medium Paranapanema River, municipality of Ipaussu, São Paulo State, Brazil. Twenty-three fish species were analysed, and 13 were infected with A. compactum metacercariae (56.5%) in their eyes. The following six fish species are new hosts for this metacercaria: Crenicichla haroldoi (1/1), Eigenmannia trilineata (11/6), Hoplosternum littorale (11/1), Iheringichthys labrosus (17/2), Leporinus amblyrhynchus (11/1), and Piaractus mesopotamicus (3/1). These new species increase the number of Brazilian fish species infected with this parasite to 36. Based on these findings, we hypothesise that the metacercariae larval stage of the parasite has a low specificity for the second intermediate host (fish). The majority of fish species infected in Brazil belong to the Loricariidae and Cichlidae families. For the fish species with higher mean abundances in Brazil, six are non-native species, and currently, Plagioscion squamosissimus has the highest mean abundance. The majority of fish species infected with A. compactum in Brazil are concentrated in the Paraná basin, although this may be related to the distribution of researchers.

Assessing fish assemblages similarity above and below a dam in a neotropical reservoir with partial blockage.

Damming rivers disrupts the water flow and changes the ichthyofauna organisation. We investigated an impoundment with permanent connection and homogeneous environmental conditions between the zones above and below the dam. Temperature was comparatively higher during wet season irrespective of zone, and both zones had higher dissolved oxygen, conductivity and transparency in the dry season. A total of 1687 individuals comprising 27 species were collected in the downriver zone, while the reservoir had 879 individuals and 23 species. Each zone had different fish assemblage composition and structure, but assemblages were not explained by the examined environmental variables (r2 = 0.08; p = 0.307). Migratory species such as Pimelodus maculatus, Pimelodus fur, Leporinus copelandii and Prochilodus lineatus were the most affected, and probably are prevented to perform upriver migrations. On the other hand, lentic adapted species such as G. brasiliensis, Hoplias malabaricus and Hoplosternum littorale successfully colonised the reservoir. Therefore we conclude that the presence of the lateral hydrological connectivity alone does not guarantee the ecological connectivity since fish assemblage similarity differed between the two zones. Fish passage facilities should be monitored and managed to evaluate and improve their functionality.

Population features of Hoplosternum littorale (Hancock, 1828) (Siluriformes, Callichthyidae) at Santo Anastacio Reservoir, Brazil

ABSTRACTObjective. The length-weight relationship and condition factor of fish are indicators of physiological well-being and may be related to reproduction and feeding periods. These attributes were evaluated for a population of Hoplosternum littorale sampled in the Santo Anastácio Reservoir (Fortaleza, Northeastern Brazil). Materials and methods. One hundred and fifty-five specimens were collected with gillnets between October 2009 and March 2010, and standard length (cm), total weight (g), sex and gonadal maturation stage were registered. Results. The observed length-weight relationship indicated negative allometric adjustment (2.72). Only seventy individuals were evaluated for the condition factor analysis, sexual determination and gonadal state classification. Condition factor values peaked in November and plummeted in February, no statistical differences in sex ratio (χ²=13.683; p=0.057) were observed. Mature females were collected throughout the study period. Conclusions. The results indicate that the population of H. littorale in the Santo Anastácio reservoir presents growth deficiency and changes in reproductive strategy in this hypereutrophic environment.

Dieta e Ritmo Circadiano da Atividade Alimentar do Tamoatá Hoplosternum Littorale (Hancock, 1828) (Siluriformes, Callichthydae) Capturados no Rio Vacacaí, Rio Grande do Sul, Brasil

O presente trabalho tem como objetivo contribuir com os conhecimentos biológicos e ecológicos de Hoplosternum littorale através do estudo de sua dieta no Rio Vacacaí, RS. Para tal, foram realizadas coletas em todas as estações do ano em quatro pontos escolhidos ao longo do Rio Vacacaí, utilizando-se redes de espera com malhas 1,5; 2,0; 2,5; 3,0; 4,0; 5,0; 6,0 e 8,0 cm entre nós adjacentes. As redes permaneceram na água por 24 horas, sendo revisadas a cada seis horas. Os peixes capturados foram fixados em formol 10% e posteriormente conservados em álcool 70%. Os exemplares foram pesados, medidos e tiveram o trato digestório retirado para a análise da dieta. Os itens encontrados no conteúdo estomacal foram separados em seis categorias: Insetos, Moluscos, Detrito/Sedimento, Vegetais, Escamas e Nematoides, sendo cada categoria analisada pelos métodos de frequência de ocorrência e volumétrico, sendo estes combinados posteriormente para se obter o Índice Alimentar (IAi). O Grau de Repleção estomacal (GR) e o Índice de Repleção (IR) também foram estimados para avaliar a atividade alimentar de acordo com o ritmo circadiano. Os itens mais importantes na dieta dessa espécie de acordo com o IAi foram insetos, detrito/sedimento e vegetais. H. littorale apresentou maior atividade alimentar no inicio da manhã, coincidindo com uma maior captura também na revisão deste horário, o que sugere uma atividade noturna.