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Coastal rivers provide habitat for fishes that have developed life-history strategies to take advantage of low salinity and high structural complexity. The coastal rivers of southeastern Florida have been ranked high for restoration at a national scale by conservationists because of the great potential for projects to benefit both human assets and aquatic communities. To help prioritize projects, a fisheries-independent monitoring dataset was analyzed to identify fish habitat using hotspot analysis and habitat suitability. An initial examination testing for broad seasonal changes (high vs. low freshwater inflow) in species distributions showed little change; thus, we concluded that static habitat (e.g., geomorphological features, shore types) was important for supporting fishes in this system. A river section, North Fork St. Lucie River, located 23–45 km from the river mouth and comprised of braided river channels and mangrove backwaters was a hotspot for economically important species such as common snook and red drum. The same river stretch supported a suite of regionally unique tropical species including opossum pipefish, smallscale fat snook, and bigmouth sleeper that had affinities for low salinity. Species were partitioned within this river stretch by salinity, depth, and shore type (e.g., smallscale fat snook compared to common snook used shorelines that were fresher, deeper, and had fewer mangroves). Restoration efforts can be prioritized by (1) maintaining low salinity (< 15) and reconnecting floodplains and riverine backwaters in the North Fork St. Lucie River, an area comprised of fish hotspots, and (2) exploring strategies to improve fish habitat in other areas currently less used.

Centropomus undecimalis (common snook) and Centropomus parallelus (fat snook) have a wide distribution from southern Florida to southern Brazil. Due to their value as a food source, these species have been heavily exploited through predatory fishing, posing a conservation challenge. To assess their genetic diversity and population structure, we used microsatellite markers. Our findings revealed genetic differences among populations of the same species, highlighting the need for targeted conservation efforts. The microsatellite markers proved effective in assessing genetic variability, providing valuable insights for management and conservation. The parameters Ho (observed heterozygosity) and He (expected heterozygosity) were reliable indicators of genetic diversity, and specific loci showed varying allele numbers across populations. Our study contributes to understanding population genetics in these snook species and supports their conservation. Despite not being classified as endangered, genetic differences among populations emphasize the importance of considering population-level characteristics in conservation strategies. This research lays the foundation for future studies and actions aimed at preserving these valuable fish species. In summary, our study demonstrates the significance of microsatellite markers in assessing genetic variability and population structure in common snook and fat snook, informing conservation efforts for these species.

The presence of relatively rare species in estuarine fish communities can influence niche differentiation among species, functional redundancy, and ecosystem stability when faced with environmental disturbance. In southeastern Florida, at least four species of snook (Centropomidae) occur in coastal river systems, but only one species occurs elsewhere in the state. To better understand how these species can co-occur, we analyzed data from electrofishing and diet studies conducted during 2007–2010 to investigate niche partitioning between two species: Common Snook Centropomus undecimalis and Smallscale Fat Snook Centropomus parallelus (common and fat snook hereafter). Although the diets of the two species collected from coastal rivers were barely distinguishable, there was separation of habitat use. Adult fat snook had affinities for low salinity portions of rivers, while common snook were distributed more widely. Use of nursery habitat by fat snook occurred during early spring, confirming winter spawning, which contrasts with the protracted spawning of common snook that occurs spring through fall. While in riverine nurseries, juvenile fat snook occupied shallow to moderate depths with cover (e.g., woody debris, docks); common snook had greater affinity for shallow natural shorelines (e.g., mangroves, aquatic macrophytes). Overall, fat snook appeared to occupy niches left open by the generalist common snook. Considering that centropomids are likely to expand their range northward in Florida with climate change, understanding habitat use and niche partitioning among the species may help predict which species is likely to expand first and what habitat types will be occupied.

Fishers’ ecological knowledge (FEK) has contributed to a better understanding about the reproduction of fishery resources, especially where biological data are scarce or unavailable. We analyzed FEK on the reproduction of five fishery resources in the Paranaguá estuarine complex and adjacent coastal area, Brazil, including fishes (Genidens barbus, Centropomus parallelus, Chaetodipterus faber, Pseudobatos sp.) and shrimp (Litopenaeus schmitti). We also sought to compare FEK with biological data and investigate which characteristics (age, fish evisceration and fishers’ location) influence fishers' knowledge. We interviewed 132 artisanal fishers. FEK indicated reproductive peaks in the spring and summer for the fish species and in late winter and early spring for the shrimp. The maturation sizes according to FEK did not differ from sizes at first maturity (L50) as reported by biological studies for G. barbus and L. schmitti. Fishers’ residence sites and fish evisceration influenced more their knowledge related to species reproduction than age. Fishers showed a detailed ecological knowledge about some reproductive aspects, including size at first maturity of females, site of occurrence and reproductive peaks. Furthermore, fishers were able to identify sexual dimorphism, parental care and ovoviviparity. These results can be applied to improve fisheries management in the context of data poor fisheries.

Metal contamination is a threat to estuarine environments. They can accumulate in the food chain and cause toxic effects on aquatic organisms and human health. This study evaluated the concentrations of metals (Cd, Cr, Cu, Fe, Ni, Pb, and Zn) in aquatic organisms of Antonina Bay (southern Brazil) to analyze whether the metal concentrations were in accordance with Brazilian food legislation and estimate the human risk of local seafood consumption. All analyzed organisms ( Centropomus parallelus , Mugil curema , Genidens genidens , Crassostrea brasiliana , and Xiphopenaeus kroyeri ) showed traces of metals in their tissues with different metal concentrations among species. Metal concentrations were generally higher in oyster C. brasiliana , and biomagnification was not observed. Cr and Zn concentrations were above the limits established by legislation for all species in at least one sample. The concentrations of the other metals were within permitted levels. However, concentrations of Cd, Cr, Fe, and Zn posed a human consumption risk. In general, the C. brasiliana oyster presented the highest risk for human consumption, probably due to its filtering habit. Thus, the results indicated that metal concentrations in the tissues of the Antonina Bay seafood can pose a risk to human health, and this chronic exposure to metals also can cause toxic effects on local aquatic biota.

Abstract Aim The objective was to describe the LWR of fish species of the Guaraguaçu River, as well as to compare the LWR parameters of the non-native species with the parameters obtained in their native ranges, available in the literature. Methods In this study, the LWR of 10 fish species of the Guaraguaçu River, southern Brazil, were analyzed. Fish were sampled semiannually between 2004 and 2007, using different sampling techniques in the Guaraguaçu River. Results A total of 673 specimens of 10 species were captured. The LWR demonstrated a prevalence of species (six out of 10) with positive allometric growth (b > 3). The remaining species presented isometric (b = 3, two species) or negative growth (b < 3, two species). Native species exhibited the same LWR from previous studies, except Centropomus parallelus, which presented an isometric growth in this study. The non-native species Clarias gariepinus and Ictalurus punctatus showed significant differences between the LWR parameters in the Guaraguaçu River and in their native distribution, but the same growth pattern. Oreochromis niloticus did not present significant differences in the allometric coefficient from its native range. Conclusions These results indicate that different environmental conditions may not influence the growth pattern of non-native species, which explains their invasion success due to high adaptability to new environments. Resumo Objetivo O objetivo foi descrever os parâmetros LWR das espécies nativas e não nativas do rio Guaraguaçu e comparar esses parâmetros das espécies não nativas obtidos no rio Guaraguaçu com os parâmetros de LWR dos seus locais de distribuição nativa disponível na literatura. Métodos Os exemplares foram coletados semestralmente entre 2004 e 2007, usando diferentes técnicas de amostragens. Resultados No total, foram analisados 673 exemplares de 10 espécies. Seis espécies apresentaram alometria positiva (b>3) e três alometria negativa (b<3) e isometria (b=3). Espécies nativas possuem parâmetros de LWR idênticos a estudos prévios, exceto Centropomus parallelus, a qual apresentou isometria neste estudo. As espécies não nativas Clarias gariepinus e Ictalurus punctatus demonstraram diferenças significativas entre os parâmetros de LWR do Guaraguaçu e das suas áreas de distribuição nativa. Oreochromis niloticus não apresentou diferença significativa entre os parâmetros de LWR entre o Guaraguaçu e sua área nativa de distribuição. Conclusões O resultado indica que as condições ambientais talvez não influenciem o crescimento das espécies não nativas, o que explicaria o sucesso de invasão destas espécies.

The effectiveness of menthol as anesthetic and sedative for fat snook (Centropomus parallelus) was tested at different salinities. In the first experiment, the fish were exposed to different concentrations of menthol (25, 37 and 50 mg L^sup -1^) in water at different salinities (0, 17 and 36 ppt). In the second experiment, the fish were transported for 10 hours in water with menthol at concentrations of 0, 3.7 and 7.4 mg L^sup -1^ under different salinities. Na^sup +^ and K^sup +^ ions from fish body and water were analyzed after transport. The optimal concentrations of menthol for a short handling period and surgical induction was 37 and 50 mg L^sup -1^, respectively, and these values were independent of salinity. After transport, neither mortality nor significant changes in ammonia or dissolved oxygen were observed between treatments at the different salinities. The nitrite levels were lower in freshwater than in brackish and saltwater, but did not change with mentol. The total body levels of Na^sup +^ increased with the salinity increase. Menthol is an effective anesthetic for handling of juvenile fat snook at different salinities. Menthol did not influence the measured water parameters and body ions, and it is not necessary for the transport of fat snook.

Development of the digestive tract and accessory glands of larvae of the fat snook Centropomus parallelus was examined under light microscopy, from hatching to 60 day post-hatching (dph). At hatching, the digestive tract is straight and composed by a cubic cell layer. The exogenous feeding starts at 3 dph, concomitantly with the mouth opening and subdivision of the rudimentary stomach and esophagus. At 4 dph, the intestine has three sectins, and vacuoles are observed in the posterior section, indicating the beginning of protein digestion and absorption. The pharyngeal teeth appear at 9 dph, and goblet cells appear at 13 dph in the esophagus. Gastric glands appear at 30 dph, marking the beginning of weaning. The disappearance of supranuclear vacuoles in the posterior intestine occurs at 35 dph, suggesting efficiency of extracellular digestion. This study shows that C. parallelus larvae is able to start weaning 15 days earlier than reported in earlier studies, increasing the success of larviculture.

Summary The objective of this study was to isolate and select autochthonous strains of Bacillus subtilis from the fat snook, Centropomus parallelus, and examine the viability of the Bacillus bacteria to determine their beneficial effect on gut colonization in reared fish. Twenty strains of Bacillus were isolated and further confirmed as B. subtilis using PCR. Among the 20 strains, two strains (B02 and B03) exhibited an inhibitory performance against five tested pathogens. The Bacillus strains B02 and B03 were added to the fish ration, and after 30 days the number of viable colonies were maintained or increased under the conditions of refrigeration (5°C), freezing (−18°C), or room temperature (30°C). These strains showed a growth rate of 0.18–0.21 h and a doubling time of 3.34–3.9 h. Both strains were tolerant to variations in NaCl, and B03 was also tolerant to bile exposure. The ability to colonize the gastrointestinal tract was also examined in healthy fat snook juveniles fed diets enriched for 30 days with strains B02 and B03. The amount of B. subtilis in the gastrointestinal juvenile tract was significantly higher in fish fed the enriched ration compared to controls. Based on these results, strains B02 and B03 were considered as candidate probiotics for fat snook.

The aim of this study was to determine the level of dietary crude protein (CP) (480, 400, 440, 520 and 560g kg-1) in rations for juvenile II fat snook (Centropomus parallelus) that best promotes protein absorption and lower excretion of nitrogenous products. Three experiments were conducted: the first assessed the protein retention rate; the second evaluated ammonia excretion; and the third determined the best digestibility coefficient. The estimated protein retention rate showed a positive quadratic response to dietary CP with maximum retention at the 510.20g kg-1 protein level, and increasing levels of protein resulted in a greater total ammonia excretion rate in water. The mean apparent protein digestibility coefficient values increased with increasing levels of dietary protein up to 520g kg-1, where they stabilized. As determined by regression, the level of dietary CP that promotes the best digestibility was 495.62g kg-1. RESUMO: O objetivo da pesquisa foi determinar o nível de proteína bruta na dieta (400, 440, 480, 520 e 560g kg-1), nas rações de juvenis II de robalo-peva (Centropomus parallelus), que promove melhor absorção de proteína e menor excreção de produtos nitrogenados. Foram realizados três experimentos. O primeiro avaliou a taxa de retenção de proteína, o segundo a excreção de amônia, e o terceiro determinou o melhor coeficiente de digestibilidade. Os dados foram analisados por meio de regressão exponencial. A taxa de retenção proteica, calculada pela equação, apresentou efeito quadrático positivo e o máximo de retenção com 510,20g kg-1 de proteína na dieta. O aumento dos níveis de proteína resultou em maiores taxas de excreção de amônia total na água. Os valores médios dos coeficientes de digestibilidade aparente da proteína foram aumentando com o aumento da proteína dietética até o nível de 520g kg-1 onde se estabilizou. O nível de proteína bruta na dieta, determinado pela equação de regressão, que promove a melhor digestibilidade é de 495,62g kg-1.