Structure of the phytoplankton community in the Cachoeira Dourada reservoir (GO/MG), Brazil

The limnological features and the phytoplankton community of the Cachoeira Dourada reservoir were analyzed in December 2006, May 2007 and November 2007. Temporal changes in the taxonomic composition, density, diversity and dominance of species were analyzed in relation to climatic factors and the physical and chemical characteristics of the water. A positive correlation was found between some of the physical and chemical variables and the phytoplankton community. According to the CCA, variables such as the extent of the euphotic zone, temperature, pH, nitrogen and phosphorus concentrations directly affected the phytoplankton dynamics. Organisms belonging to the class Cyanophyceae were the most representative in all the sampling periods, comprising the functional groups K, S1, M and H. Hydrodynamics and seasonal fluctuations of environmental factors were the driving forces determining the composition and abundance of the algal assemblages. Despite the prevalence of Cyanobacteria, the reservoir is still oligotrophic. The absence of blooms and the relatively low population abundances indicated that the quality of the reservoir's water still lies within the limits required for its multiples uses

Growth and reproduction aspects of Pimelodus maculatus Lacépède, 1803 (Siluriformes, Pimelodidae) of the Cachoeira Dourada reservoir, state of Goiás and Minas Gerais, Brazil

Growth and reproduction parameters of the yellow-mandi, Pimelodus maculatus Lacépède, 1803 (Siluriformes, Pimelodidae), were determined for the Cachoeira Dourada reservoir (GO/MG). The field work occurred throughout February 2007 to January 2008 (with the exception of December 2007). Gill nets with mesh sizes from 1.5 to 10 centimeters were placed in three different areas in the reservoir and were collected 24 hours later. A total of 538 specimens were captured, amongst which 242 were females, 219 were males and 77 could not have their sex determined. Sex ratio differed from 1:1 only during July 2007 and January 2008, with males and females predominating in each of those months. Males occupied the medium length classes (18.9 to 24.3 cm) while females were most abundant in the superior classes (from 27 to 37.8 cm).The growth constant K was statistically equal for males (K=0.1851) and females (K=0.1708), however, females P. maculatus may have a greater investment in reproductive tissue, a fact indicated by the elevated values of Kn and GSI during the summer. Bearing in mind that P. maculatus reproduces in the rainy season, a greater gain in weight is expected during the months before the reproduction season, and that after it occurs the fish loses fat and weight as a consequence of metabolic effort. Still, the absence of juveniles may be an indication that the species did not find in the reservoir the proper conditions for reproduction and growth of its fry

Feeding habits of the congeneric species Stellifer rastrifer and Stellifer brasiliensis (Acanthopterygii: Sciaenidae) co-occurring in the coast of the state of Santa Catarina, Brazil

The objective of the present study was to investigate the feeding habits allowing the occurrence of the congeneric species Stellifer rastrifer and Stellifer brasiensis, collected on a seasonal basis, in the operating area of the artisanal seabob-shrimp trawl fishery in Porto Belo, an important fishing area on the southern Brazilian coast. Fish were collected seasonally from November 2009 to August 2010, in isobaths of 10, 20 and 30m. Of the 450 stomachs analyzed, 194 belongd to Stellifer rastrifer and 242 to Stellifer brasiliensis. From the totality of analyzed stomachs 33.49% were empty and 66.52% had some content. Crustacea were the predominant food category in the diet of S. rastrifer and S. brasiliensis, and the shrimp Acetes americanus was the most frequent crustacean in stomachs of both studied species. The overlapping in the diet of the species was high, however when analyzing the overlap in each season it was found that it occurred only during spring and winter. Although the most important items in the diet of these species are the same, the intake of each alternates in time, suggesting a difference in predation pressure, which leads to less direct competition in a given time

The influence of population structure and reproductive aspects of the genus Stellifer (Oken, 1817) on the abundance of species on the southern Brazilian coast

The differences between abundance and the relationship with aspects of population and reproductive Stellifer rastrifer, Stellifer stellifer and Stellifer brasiliensis were analysed. Data were collected monthly trawl directed for capture of seabob shrimp in Armação do Itapocoroy, an important fishing area on the southern Brazilian coast. The chi-square test showed that the population of S. rastrifer presented values of capture significantly higher than others in all evaluated periods. The frequency distribution of total length curves combined with records of the size at first maturity (L50) showed that S. rastrifer is a species with a majority of the adults effectively participating in the reproductive period. The frequency of occurrence of individuals in reproduction monthly examined together with changes in the gonadosomatic index (GSI) and the reproductive activity index indicated that spring was the main breeding season for the three species. However, it was observed that the reproductive period of S. rastrifer was more pronounced and more extensive than that of its congeners, apparently providing it with ecological advantages and enabling a more effective population balance given the pressure exerted by fishing in the study area

Feeding habits of the congeneric species Stellifer rastrifer and Stellifer brasiliensis (Acanthopterygii: Sciaenidae) co-occurring in the coast of the state of Santa Catarina, Brazil

The objective of the present study was to investigate the feeding habits allowing the occurrence of the congeneric species Stellifer rastrifer and Stellifer brasiensis, collected on a seasonal basis, in the operating area of the artisanal seabob-shrimp trawl fishery in Porto Belo, an important fishing area on the southern Brazilian coast. Fish were collected seasonally from November 2009 to August 2010, in isobaths of 10, 20 and 30m. Of the 450 stomachs analyzed, 194 belongd to Stellifer rastrifer and 242 to Stellifer brasiliensis. From the totality of analyzed stomachs 33.49% were empty and 66.52% had some content. Crustacea were the predominant food category in the diet of S. rastrifer and S. brasiliensis, and the shrimp Acetes americanus was the most frequent crustacean in stomachs of both studied species. The overlapping in the diet of the species was high, however when analyzing the overlap in each season it was found that it occurred only during spring and winter. Although the most important items in the diet of these species are the same, the intake of each alternates in time, suggesting a difference in predation pressure, which leads to less direct competition in a given time

The influence of population structure and reproductive aspects of the genus Stellifer (Oken, 1817) on the abundance of species on the southern Brazilian coast

The differences between abundance and the relationship with aspects of population and reproductive Stellifer rastrifer, Stellifer stellifer and Stellifer brasiliensis were analysed. Data were collected monthly trawl directed for capture of seabob shrimp in Armação do Itapocoroy, an important fishing area on the southern Brazilian coast. The chi-square test showed that the population of S. rastrifer presented values of capture significantly higher than others in all evaluated periods. The frequency distribution of total length curves combined with records of the size at first maturity (L50) showed that S. rastrifer is a species with a majority of the adults effectively participating in the reproductive period. The frequency of occurrence of individuals in reproduction monthly examined together with changes in the gonadosomatic index (GSI) and the reproductive activity index indicated that spring was the main breeding season for the three species. However, it was observed that the reproductive period of S. rastrifer was more pronounced and more extensive than that of its congeners, apparently providing it with ecological advantages and enabling a more effective population balance given the pressure exerted by fishing in the study area