TEMPORAL VARIATION IN LARVAL ABUNDANCE OF THE MANGROVE OYSTER Crassostrea sp. IN AN ESTUARY OF SOUTHERN BRAZIL

An alternative for reducing the degree of exploitation of natural oyster banks is to use artificial seed collectors. The effectiveness of said seed collectors, however, depends on the knowledge of the cycles and abundance of larvae in the plankton. This work aimed to study the presence of larvae of the genus Crassostrea in the Guaratuba Bay, which is located on the southern coast of Brazil, using two complementary methods: 1) visual identification followed by larval counts and 2) identification of the larvae at the species level using molecular biology. Measurements of abiotic parameters related to water quality (concentration and saturation of dissolved oxygen, pH, temperature, salinity and transparency) were performed every two weeks at three sampling points (Cabaraquara, Ilha da Sepultura and Parati) from January 2010 to April 2011 (n=32), and plankton was collected in 65 µm nets for larval research. Environmental parameters, particularly pH and the concentration of dissolved oxygen, influenced the presence of mollusc larvae in the Guaratuba Bay. The highest concentrations of larvae in the plankton occurred between September 2010 and January 2011, and the variation in larval abundance was observed mainly during the warmer seasons of the year (spring and summer).

IMPROVING PRODUCTION OF SOFT-SHELLED SWIMMING CRABS: MACROSCOPIC SIGNS OF MOLTING AS A TOOL FOR SELECTION AND MANAGEMENT OF Callinectes danae AND Callinectes exasperatus (PORTUNIDAE, DECAPODA, CRUSTACEA)

In order to improve the efficiency of soft-shell crab production, we investigated whether it is technically viable to increase harvesting rates of soft-shelled crabs of the species Callinectes danae and C. exasperatus by selecting animals based on macroscopic molt signs and maintaining them in specific facilities. The study was conducted in three stages. In the first stage, macroscopic anatomic changes possibly related to the molting cycle identified under laboratory conditions. In the second stage we used the macroscopic clues observed in the first assay to select premolt animals harvested from their natural environments. Yet in this stage of the work, the relationship between the macroscopic changes and the microscopic signs of molting was evaluated. Lastly, an assay verified the technical feasibility of increasing the fraction of soft-shells in the total catch by selecting and maintaining premolt swimming crabs of species C. danae and C. exasperatus in specific facilities until the molt. Our results indicated that we can macroscopically identify, and therefore select, individuals in premolt phases II, III and IV that will soon molt, but further investigations are necessary to identify the requisite conditions for successful molting of individuals in premolt phase I

Diversidade ictiofaunística de três tributários do rio São Francisco, Brasil

We evaluated fish diversity in three tributaries of the São Francisco River, one of the largest watercourses in Brazil. The study site is in the sub-basin of the Carinhanha River [Carinhanha, Cocos (I and II) and Itaguari Rivers], located in the South region of the Bahia state. These rivers are crossed by bridges of the federal highway BR-135. After sampling, upstream and downstream from each bridge, during drought and rain seasons, 3,520 specimens of fish (57 species, 21 families) were captured. The species with highest occurrence were Astyanax cf. taeniatus, Serrapinnus heterodon, Astyanax bimaculatus and Astyanax cf. rivularis. During drought season, the number of specimens captured was higher, leading to an increase of species dominance. In the rainy season, species diversity was higher with a greater distribution of individuals among species. The data indicate the maintenance of the fish faunal structure despite anthropogenic activities on the studied areas.O presente estudo fornece informações sobre a diversidade de peixes em três tributários do rio São Francisco, um dos mais importantes cursos d'água do Brasil e da América do Sul. A área de estudo, localizada na sub-bacia do rio Carinhanha (rios Carinhanha, Cocos segmento I e II e Itaguari), no estado da Bahia, envolve rios que estão em processo de interceptação pela rodovia federal BR-135. Amostragens realizadas tanto a jusante quanto a montante da rodovia, em períodos de seca e de chuva, levaram à captura de 3.520 exemplares (57 espécies; 21 famílias). As espécies de maior ocorrência foram Astyanax cf. taeniatus, Serrapinnus heterodon, Astyanax bimaculatus e Astyanax cf. rivularis.  No período de seca houve maior número de capturas e dominância de espécies. No período chuvoso registrou-se maior diversidade de espécies e maior distribuição de indivíduos entre as espécies. Os dados indicam a manutenção da estrutura ictiofaunística, apesar das ações antrópicas sofridas pelos ambientes estudados

RESPOSTAS ADAPTATIVAS DE PEIXES A ALTERAÇÕES AMBIENTAIS DE TEMPERATURA E DE OXIGÊNIO DISSOLVIDO

Cada vez mais, os ambientes aquáticos têm sofrido pressões tanto de origem natural quanto antrópica. Por estes motivos os organismos que habitam estes ecossistemas são forçados a se adaptar às novas condições ou poderão ser extintos. O estudo para compreensão destas transformações ambientais pode ser feito por meio do uso de animais indicadores, dentre os quais os peixes se destacam. Isto porque os peixes refletem as modificações ocorridas no ambiente aquático por meio de respostas adaptativas tão variadas quanto: (1) ajustes fisiológicos e bioquímicos quando peixes são expostos a diferentes temperaturas e (2) por alterações identificadas em peixes submetidos a baixas concentrações de oxigênio dissolvido na água. Este estudo foi desenvolvido com o objetivo de avaliar de que maneira os peixes podem ser utilizados como organismos indicadores das alterações ambientais relacionadas à temperatura e à variação de oxigênio dissolvido e entender melhor a interação destes animais com o ambiente

Effects of salinity on the survival and histology of oysters Crassostrea gasar (Adanson, 1757)

Water salinity is among the most important factors influencing the distribution, abundance, growth, and survival of Crassostrea gasar, an important aquaculture resource grown in estuarine environments in diverse regions of the world. The goal of the present work was to evaluate the effects of different salinities on survival and the tissues of C. gasar under laboratory conditions. Two experiments were performed using adult oysters from five marine farms located in the bay of Guaratuba, Brazil. In Experiment 1, the daily survival rates were evaluated after the oysters were submitted to gradual acclimatization at salinities ranging from 0 to 65 gL-1 and maintained in the laboratory without feeding for up to 365 days. In Experiment 2, the oysters were exposed to salinity from 0 to 50 gL-1 for up to 30 days without feeding and possible histological alterations caused by salinity were assessed. Three tolerance ranges of C. gasar to salinity were identified: "Optimal" (between 4 and 40 gL-1), "Tolerable" (between 2.1 and 3.9 and between 41 and 50 gL-1) and "Intolerable" (less than 2 and greater than 50 gL-1). No evidence of histological alterations was observed in oysters exposed to the different salinities

From egg to slaughter: monitoring the welfare of Nile tilapia, Oreochromis niloticus, throughout their entire life cycle in aquaculture

The primary aim of this study was to comprehensively evaluate the welfare of Nile tilapia (Oreochromis niloticus) throughout their entire life cycle within aquaculture, spanning from reproduction to slaughter. The methodology was structured to identify welfare indicators closely aligned with the principles of animal freedoms defined by the Farm Animal Council, encompassing environmental, health, nutritional, behavioral, and psychological freedom. Notably, psychological freedom was inherently considered within the behavioral and physical analyses of the animals. To accomplish this, an integrative systematic literature review was conducted to define precise indicators and their corresponding reference values for each stage of tilapia cultivation. These reference values were subsequently categorized using a scoring system that assessed the deviation of each indicator from established ideal (score 1), tolerable (score 2), and critical (score 3) ranges for the welfare of the target species. Subsequently, a laboratory experiment was executed to validate the pre-selected health indicators, specifically tailored for the early life stages of tilapia. This test facilitated an assessment of the applicability of these indicators under operational conditions. Building on the insights gained from this experimentation, partial welfare indices (PWIs) were computed for each assessed freedom, culminating in the derivation of a general welfare index (GWI). Mathematical equations were employed to calculate these indices, offering a quantitative and standardized measure of welfare. This approach equips tilapia farmers and processors with the tools necessary for the continuous monitoring and enhancement of their production systems and stimulate the adoption of more sustainable and ethical practices within the tilapia farming

Comparação morfométrica entre megalopas do caranguejo do mangue produzidas em laboratório e capturadas na natureza

The objective of this work was to compare the morphometry of hatchery‑reared and wild‑caught mangrove crab (Ucides cordatus) megalopae. Ten U. cordatus megalopae of each group (hatchery‑reared and wild‑caught) were individually analyzed using a stereoscopic microscope equipped with an ocular micrometer. Length, width, and height of all megalopae were measured, and the size of body appendices was determined. The results indicate that the hatchery‑reared megalopae are more robust than the wild ones. Furthermore, some significant differences in the size of certain appendices can be cues of the kind of alterations that hatchery‑reared individuals experience.O objetivo deste trabalho foi comparar a morfometria de megalopas de caranguejo do mangue (Ucides cordatus) produzidas em laboratório e capturadas na natureza. Dez megalopas de U. cordatus de cada grupo (produzidas em laboratório e capturadas na natureza) foram analisadas individualmente utilizando microscópio estereoscópico equipado com ocular micrométrica. Comprimento, largura e altura de todas as megalopas foram medidos, e o tamanho dos apêndices corporais foi determinado. Os resultados são indicativos de que as megalopas produzidas em laboratório são mais robustas que as selvagens. Além disso, algumas diferenças significativas no tamanho de certos apêndices podem ser pistas do tipo de alterações que os indivíduos produzidos em laboratório experimentam

Monitoring fish communities through environmental DNA metabarcoding in the fish pass system of the second largest hydropower plant in the world

The Itaipu Hydroelectric Power Plant is the second largest in the world in power generation. The artificial barrier created by its dam imposes an obstacle for fish migration. Thus, in 2002, a fish pass system, named Piracema Channel, was built to allow fish to access areas upstream of the reservoir. We tested the potential of environmental DNA metabarcoding to monitor the impact of both the dam and associated fish pass system in the Paraná River fish communities and to compare it with traditional monitoring methods. Using a fragment of the 12S gene, we characterized richness and community composition based on amplicon sequence variants, operational taxonomic units, and zero-radius OTUs. We combined GenBank and in-house data for taxonomic assignment. We found that different bioinformatics approaches showed similar results. Also, we found a decrease in fish diversity from 2019 to 2020 probably due to the recent extreme drought experienced in southeastern Brazil. The highest alpha diversity was recorded in the mouth of the fish pass system, located in a protected valley with the highest environmental heterogeneity. Despite the clear indication that the reference databases need to be continuously improved, our results demonstrate the analytical efficiency of the metabarcoding to monitor fish species

Testing a molecular protocol to monitor the presence of golden mussel larvae (Limnoperna fortunei) in plankton samples

The golden mussel (Limnoperna fortunei, Mollusca: Mytilidae) is an emerging invasive species in freshwater environments in South America, causing extensive environmental and economic impacts. A molecular method to detect larvae of the golden mussel in plankton samples has been recently developed and holds promise for becoming an important way to monitor the expansion of golden mussel populations. In the present study, we conduct, for the first time, field tests of this method by comparing its performance with alternative sampling efforts (microscopy and manual search for adults). In addition, we test different modifications of the molecular method to deal with PCR inhibition in environmental samples. The results indicate that the molecular method is very efficient, being faster and more sensitive that microscopy methods. Therefore, the molecular method tested in the present study can represent an invaluable tool in large-scale monitoring efforts of the golden mussel throughout its introduced range.Facultad de Ciencias Naturales y Muse