Joaquim N. S. Santos

Efeito do grau de exposição às ondas sobre a comunidade de peixes juvenis em praias arenosas do Município do Rio de Janeiro, Brasil

Vasconcellos, R.M., Santos, J.N.S., Silva, M.A. & Araujo, G. Effect of the wave exposure gradient on juvenile fish community in sandy beaches of the Rio de Janeiro City, Brazil. Biota Neotrop. Jan/Apr 2007 vol. 7, no. 1 http://www.biotaneotropica.org.br/v7n1/pt/abstract?article+bn01907012007 ISSN 1676-0603. Distribution and abundance of the ichthyofauna of surf zone in sandy beaches of the Rio de Janeiro Municipality, Brazil, were studied aiming to detect seasonal and wave exposure gradient influences on the fish community structure. Quarterly samplings were performed at 10 sites according to the exposure degree (sheltered, exposed and very exposed) between January and November 2004, by using beach seines with hauls carried out perpendicular to the coastline. A total of 6,464 fishes in 38 species and 22 families were identified, mainly juveniles or small sized individuals. The families Clupeidae, Carangidae and Sciaenidae amounted to 79% of the total fish number and 61% of the total biomass. The following species amounted to 81% of the total weight were: Harengula clupeola (36%), Orthopristis ruber (14%), Mugil liza (10%), Trachinotus goodei (8%), Trachinotus carolinus (7%) and Umbrina coroides (6%). Three species showed the highest relative abundance, contributing each one more than 10% of the total number (Harengula clupeola, Umbrina coroides, e Trachinotus carolinus); but only T. carolinus showed a clear pattern, being more abundant in the sheltered beaches. The highest CPUEs (number of individuals and biomass) and number of species values occurred in the sheltered beaches (p 0.05), although some trends were detected. The wave exposure degree was confirmed as a primary factor influencing the fish community structure, with sheltered sites probably associated to higher plankton availability, lesser turbulence and more substrate stability.

Length correction for early-juvenile Brazilian herring Sardinella janeiro (Eigenmann, 1894) after preservation in formalin, ethanol and freezing

This work aims to quantify the variation in total length and body mass for the early-juvenile Brazilian herring Sardinella janeiro and to determine total length and body mass correction equation to allow fresh measures to be calculated from preserved ones. Fishes were randomly assigned to one of five preservation methods (freezing at - 20o C, 2.5% and 5% formalin, 70% and 95% ethanol), and measured for total length (TL) and body mass (W) before preservation, and on days 5, 15, 30, and 60 after storage. Significant reductions in total length and body mass occurred during the first 5 days after preservation and continued to contract significantly at a lesser rate through 30 days in most methods. Exceptions were shown for body mass in freezing and 5% formalin, where the greatest losses occurred after 30 days of preservation. The degree of shrinkage for total length and body mass was very much dependent on fish size, with smaller specimens shrinking more than larger ones. The fresh total length and body mass can be back-calculated using equations that describe the relationship between fresh and preserved individuals after 60 days storage for all methods except for body mass in freezing.

Diel seasonality in fish biodiversity in a sandy beach in south-eastern Brazil

Diel fluctuations in nearshore fish communities were studied at a sandy beach in south-eastern Brazil. A total of 192 samples were performed by beach seines, during 3-hour intervals throughout 48-hour periods, between spring 2005 and winter 2006. Mean biomass and number of species were significantly higher at night, while number of individuals did not differ between day and night. Major disruptions in the fish community occurred during the winter when the assemblages underwent restructuring. Harengula clupeola, Sardinella janeiro, Anchoa lyoleps and Umbrina coroides were the predominant species at night, while Atherinella brasiliensis, Pomatomus saltatrix and Trachinotus carolinus peaked during the day, although significant diel changes in community structure were recorded only in the summer. Biological interactions, behavioural variations and local constraints might explain diel differences in the fish distribution. This study confirms that changes in diel activity in juvenile fish species can differ in similar areas, even for a given species, and the causes of these changes needs to be investigated.

Correction of the weight and length for juveniles Atherinella brasiliensis (Actinopterygii: Atherinopsidae) after fixation in formalin and preservation in ethanol

The present study compared losses of weight and length in specimens of Atherinella brasiliensis (Quoy & Gaimard, 1825) after fixation in formalin 10% during ten days, and posterior preservation in ethanol 70% for 45 days, in two solvents: freshwater and marine water. Additionally, correction factors were proposed to calculate the correction for weight and length from preserved specimens. The specimens were weighted and measured after collection (fresh), and with 10, 20, 27, 34, 41 and 55 days of fixation plus preservation. The largest losses in weight occurred during the first 20 days (10.35 ± 0.31% - freshwater; 11.29 ± 0.44% - marine water), continuing with lesser intensity up to the 27th day in freshwater dilution, and up to the 34th day in marine water dilution. Weight losses stabilized by the 34th day for both freshwater (11.77 ± 0.33%) and marine water (13.62 ± 0.41%). The largest losses in the total length for the two methods were also observed in the first 20 days (7.42 ± 0.27% - freshwater; 9.76 ± 0.26 - marine water), stabilizing after the 27th day in freshwater (8.60 ± 0.26%) and 20th day in marine water (9.76 ± 0.26%). The losses of weight and total length were significantly dependent on fish size, with smaller individuals suffering the most significant losses. Complete regression equations were proposed for the retro-calculation of fresh weight and total length from the preserved specimens for freshwater (Wfresh = 1.0536WP + 0.0416; TLfresh = 0.9588TLP + 5.8437) and marine water (Wfresh = 1.0868WP + 0.0451; TLfresh = 0.8621TLP + 10.425).

Habitat selection by anchovies (Clupeiformes: Engraulidae) in a tropical bay at Southeastern Brazil

Distribution of anchovies (Clupeiformes, Engraulidae) was described in the Sepetiba Bay, a coastal area of Southeastern Brazil, to assess eventual mechanisms of habitat selection. Two fish sampling programmes were accomplished; one using beach seine (1998/2000) to catch juveniles in sandy beaches, and the other, using seines (1999/2000) to catch adults in deeper bay areas. Six species representing 4 genera were recorded: Anchoa tricolor, Anchoa januaria, Anchoa lyolepis, Cetengraulis edentulus, Engraulis anchoita and Lycengraulis grossidens. Anchoa tricolor and A. januaria were the most abundant species, with the former peaking in the outer bay, while the latter peaking in the inner bay. Adults A. tricolor are target of heavy commercial fisheries in the bay during Spring-Summer, while E. anchoita, an abundant species in the continental shelf, was occasionally caught in large numbers during the Autumn. The habitat selection, by using two different bay areas, was developed by the two most abundant species, a probable mechanism to enable their coexistence.

Spawning season, recruitment and early life distribution of Anchoa tricolor (Spix and Agassiz, 1829) in a tropical bay in southeastern Brazil

The pattern of the use of the Sepetiba Bay, a semi-closed 450 km(2) area in southeastern Brazil, by Anchoa tricolor was investigated to assess spawning period, recruitment and to detect spatial-temporal patterns of this major fishery resource. Fishes were sampled by seine nets, from spring, 1998 to winter, 1999 and by beach seine, from spring, 1998 to winter, 2000. Reproductive season, measured in terms of GSI, gonad development and appearance of recruits, indicate that reproduction occurs from August to March, when they reach the best condition. Recruitment peaks in winter/spring at sandy beaches where they stay until late summer, moving toward deeper bay areas during autumn. After that, they join adults and perform movements between the bay and the adjacent continental shelf to reproduce.

Distribution of benthic fauna in sediment grains and prop roots of a mangrove channel in south-eastern Brazil

We examined the benthic fauna in four areas along a mangrove tidal channel in south-eastern Brazil, between October 2008 and August 2009. The tested hypothesis is that the most abundant groups avoid competition as they occupy different types of substrata and that the longitudinal distance from the sea also affects the occurrence of benthic fauna along the channel. We also examined the prop root epibiont fauna to describe this different community. Polychaeta was the dominant group in the sediment whereas Isopoda and Tanaidacea were the dominant groups on the prop roots. We found a tendency for higher infauna species richness and diversity in the innermost channel area during the summer. Higher abundance of epibiont fauna was also found in summer with tidal movements allowing the colonization of the prop roots of the mangrove forest by some taxa. The polychaetes Ceratocephale sp. and Laeonereis acuta had indication of habitat partitioning, with the first occurring mainly in very fine sand sediment whereas the latter preferred medium sand sediment. The microcrustaceans Chelorchestia darwini and Tanaidacea sp. 1 occurred in high abundance colonizing the prop roots. Exosphaeroma sp. was found in high abundance in infauna and epibiont fauna. The tested hypothesis of spatial partitioning of the mangrove channel by the benthic fauna was confirmed with the most abundant species occupying the substrata with different grain fractions and prop roots in different stations.

Ecomorphological relationships among four Characiformes fish species in a tropical reservoir in South-eastern Brazil

The aim of this study was to assess the ecomorphological patterns and diet of four Characiformes fish species in a poorly physically structured tropical reservoir. We tested the hypothesis that body shape and diet are associated, because environmental pressure acts on the phenotype, selecting traits according to the available resources. Ten ecomorphological attributes of 45 individuals of each species - Astyanax cf. bimaculatus (Linnaeus, 1758), Astyanax parahybae Eigenmann, 1908, Oligosarcus hepsetus (Cuvier, 1829), and Metynnis maculatus (Kner, 1858) - , collected between February and November 2003, were analyzed, and the patterns were assessed using Principal Components Analysis (PCA). Diet similarity among fish species was assessed using cluster analysis on feeding index. The first two axes from PCA explained 61.73% of the total variance, with the first axis being positively correlated with the compression index and relative height, whereas the second axis was positively correlated with the pectoral fin aspect. Two well-defined trophic groups, one herbivorous/specialist (M. maculatus) and the other formed by two omnivorous/generalist (A. cf. bimaculatus, A. parahybae) and one insectivorous-piscivorous (O. hepsetus) were revealed by the cluster analysis. Astyanax. cf. bimaculatus and A. parahybae differed. The first has comparatively greater relative height, relative length of the caudal peduncle and lower caudal peduncle compression index. However, we did not detect a close correspondence between diet and body shape in the reservoir, and inferred that the ecomorphological hypothesis of a close relationship between body shape and diet in altered systems could be not effective.