Hybrid Surubim Research Articles

Corn and cassava flours can replace wheat flour in gluten-free fish fingers

The aim of this work was to develop and to characterize fish fingers prepared with mechanically separated meat of hybrid surubim, with and without gluten. Four treatments were evaluated by varying the three steps of pre-dusting, battering, and breading. They have included wheat flour (T1), fishmeal (T2), corn flour (T3) or a blend of corn flour and cassava flour (T4). Characterization was carried out in terms of chemical, physical, microbiological, and sensory analyzes. Moisture content of the samples varied from 59.73% (T3) to 61.14% (T1), protein from 10.60% (T3) to 14.25% (T2), crude fiber from 11.00 to 11.42%, lipid from 4.42 (T1) to 10.91% (T2), and ash from 1.96% (T3) to 2.60% (T2). The highest breading yield (27.15%) coincided with the lowest shear strength (5.75 N) for T1. A darker color was observed for T2, which was prepared with fish meal. The average scores of the sensory attributes ranged from 6.12 to 7.50. All treatments presented acceptance indexes above 70%, except for the color attribute of T2. The purchase intentions for “certainly would purchase” and “possibly would purchase” were 82, 64, 72, and 72% for T1, T2, T3, and T4, respectively, with a rejection index ranging from 6 to 14%. It was concluded that treatments with corn flour (T3) and the mixture 1:1 of corn flour and cassava flour (T4) are good alternatives to replace wheat flour (T1), favoring celiac consumers.

Histopathology and molecular identification of Henneguya pseudoplatystoma

The present study proposes to characterize the parasites isolated during the initial phase of production in fish farms located in Mato Grosso do Sul in the central-western region of Brazil, using histopathology analysis and molecular techniques. A total of 340 hybrid surubim fish (Pseudoplatystoma reticulatum × P. corruscans) from four farms were examined during the co-feeding phase. Histopathology analysis showed that 10.9% (n = 37) of the fish were infected with parasites. Branchitis, lifting epithelium, hypertrophy of epithelial cells, lamellar fusion, aneurisms and infection in the bone tissue of the gill filament was observed. The parasite species was determined by amplification of the 18S rRNA gene followed by sequencing. The phylogenetic analysis of nucleotide sequences indicates a close relationship (99.6%) with Henneguya pseudoplatystoma reported to be infecting the hybrid Pseudoplatystoma. This study demonstrates the occurrence of H. pseudoplatystoma in hybrid surubim (P. reticulatum × P. corruscans) during the co-feeding phase in fish farms in Mato Grosso do Sul. Also, molecular techniques provide a faster and sensitive method to identify fish parasites, and may assist in the development of new management techniques aimed at improving the sanitary conditions contributing to the reduction of mortality rates in these animals.

Short communication: Bacillus subtilis C-3102 improves biomass gain, innate defense, and intestinal absorption surface of native Brazilian hybrid Surubim (Pseudoplatystoma corruscans x P. reticulatum)

The aim was to evaluate the effect of a diet supplemented with B. subtilis for a period of 10 days and to verify its effects on the zootechnical performance, hematological parameters, and intestinal histomorphometry of fish. The present study was designed to verify the effects of a commercial product containing Bacillus subtilis C-3102 for short administration period in the diet of Brazilian catfish Pseudoplatystoma sp. The experimental design was completely randomized with five treatments (0, 10, 20, 30, and 40 g of CALSPORIN® kg feed−1) and six replicates. Supplementation with B. subtilis did not influence (p > 0.05) on erythrogram and plasma glucose of fish. However, probiotic supplementation for 10 days was effective and caused beneficial changes in productive performance of the 30 g kg feed−1 group compared to the other groups. In addition, improvements in the immune system, such as an increase in the number of neutrophils, lymphocytes, thrombocytes, and total blood leukocytes were observed in the treated groups, besides increased height and width of the intestinal villi was possibly related with an improvement in nutrient absorption. This study shows the feasibility in to use short time of feeding in the Pseudoplatystoma sp. diet that improved the fish health.

NON-STARCH POLYSACCHARIDE IN DIETS FOR HYBRID SURUBIM: EFFECTS ON METABOLISM PLASTICITY

This study aimed to analyze the effect of mango meal, a non-starch polysaccharide, as a carbohydrate source on the metabolism plasticity and performance indicators for hybrid surubim (Pseudoplatystoma fasciatum x P. corruscans), a tropical carnivorous fish. Juveniles (±14.5g initial weight) were fed 3% of total biomass for 60 days in four experimental diets replacing 0, 33, 66 and 100% of the cornmeal. Growth by final weight was evaluated, but statistical differences (p<0.05) were not observed among the treatments. The activity of total alkaline protease was statistically lower in the fish group fed 100% cornmeal substitution. However, trypsin levels also decreased when 100% of the cornmeal was replaced by mango meal, but without statistical significance. Zymograms showed bands of protease and amylase activities for all treatments. Cholesterol (0%- 141.83±46.10; 100%- 71.36±14.40 mg.dL-1) and total protein (0%- 3.98±0.94; 100%- 1.70±1.03 mg.dL-1) in the plasma decreased as mango meal levels increased in the feed. On the other hand, glucose (0%- 105.08±31.24; 100%- 128.11±24.51 mg.dL-1) and free amino acids (0%- 24.51±2.62; 100%- 38.13±8.94 nmoles.ml-1) in the plasma increased. Although growth was not affected, the carbohydrate source affected fish metabolism, which showed metabolic adaptation by the species. The result suggests that mango meal can replace up to 33% of the cornmeal in diets for Pseudoplatystoma sp.

Production of exotic fish and Brazilian hybrids in similar conditions: Are there considerable differences of environmental performance?

In developing countries and tropical regions, earthen ponds have become an alternative for farming fish inland. Farmers usually restrict diet to compound feed, which is a relevant source of environmental impact. In the conditions described above, the motivation of this study was to evaluate the environmental impact of fish farming developed with different species. We evaluated systems producing the exotic Nile Tilapia (Oreochromis niloticus), the local hybrid Patinga (Piaractus mesopotamicus x Piaractus brachypomus) and local hybrid Surubim (Pseudoplatystoma sp. x Leiarius marmoratus). Species were bred separately, in the same farm and in similar conditions. The study was also inspired by the opportunity to properly pinpointing the most relevant reasons to explain variability of environmental performance among fish species. For this goal, we used the Life Cycle Assessment (LCA) technique, preparing our inventory by collecting realistic data, on farm, and restricting the evaluation from cradle-to-farmgate. Distinctive to many simulations in literature, we properly determined the nitrogen (N) and phosphorus (P) content of fish and feed in a bromatology Lab. To produce 1 ton of live weight, the exotic Tilapia performed considerably better than the Surubim in all impact categories evaluated. Compared to Patinga, Tilapia performed considerably better in two impact categories: water dependence and land occupation. No considerable differences were observed between the two local hybrids. For the global warming potential, the acidification potential and the eutrophication potential, feed production and fish farming were the stages that contributed the most. In general, the source of protein in feed was the predominant source of environmental impact. Indeed, terrestrial animal co-products have more embodied resources in their tissue, due to diversifying and reasonably low feed conversion rates among fish species. However, the discussion spans towards trade-offs and the puzzling situation for decision making. This includes tunneling waste for aquaculture feed instead of dumping it on the landfill, or increasing the demand for terrestrial or marine ingredients by overbalancing in some direction. At the same time, the pathway towards sustainability of fish farming systems relies on finding alternative ingredients and managing genetic resource in order to improve feed conversion rates, empower and speed up production. For sure, these tasks demand efforts to meet the nutrient requirements of fish and offer feed with suitable composition. Overall, the methodology presented in this study can be used to compare and demystify environmental performances among local and exotic genetic resources.

Dietary protein:lipid ratio changes growth, digestive enzyme activity, metabolic profile and haematological parameters in hybrid surubim (Pseudoplatystoma fasciatum × Leiarius marmoratus)

Studies investigating improved protein:lipid ratios based on their effects on growth, nutrient utilization, digestive enzyme activities, blood metabolites and erythogram in tropical carnivorous fish are very scarce. This study evaluated the effect of different protein:lipid ratios on these parameters in the hybrid surubim Pseudoplatystoma corruscans × Leiarius marmoratus. Juvenile fish (8.90 ± 0.94 g initial weight) were fed 3% of total biomass for 60 days using four isoenergetic experimental diets with different protein:lipid ratios (9.00, 4.60, 3.54 and 1.78). Higher growth performance parameters were observed at higher protein:lipid ratios. The activities of intestine total alkaline protease, trypsin and lipase (U/mg protein) were not affected by dietary treatments. Chymotrypsin (U/mg protein) was higher in the 4.60 protein:lipid ratio group. Amylase (U/mg protein) was higher in intermediate groups. Blood glucose, total plasma protein, triglycerides, cholesterol and free amino acids decreased as the protein:lipid ratio decreased. Haematocrit was higher at the 9.00 and 4.60 protein:lipid ratios. Hybrid surubim showed metabolic adaptation to the different protein:lipid ratios tested. These results suggest that the 4.60 protein:lipid ratio showed the best protein-sparing effect of lipids.

Genetic variability of pure Pseudoplatystoma corruscans and Pseudoplatystoma reticulatum individuals in the Paraná and Paraguay River basins

The presence of interspecific hybrid surubim (Pseudoplatystoma corruscans × Pseudoplatystoma reticulatum) in natural environments can put at risk the existence of the pure parental lineages. The aim of this study was to characterize the genetic variability of pure Pseudoplatystoma corruscans and Pseudoplatystoma reticulatum individuals from rivers in the Parana and Paraguay basins in Brazil. Seventy-six pure individuals of P. corruscans and 16 of P. reticulatum were evaluated with six microsatellite loci for both species, along with one species-specific locus each for P. corruscans and P. reticulatum. Loss of heterozygosity was confirmed, and preservation measures for P. corruscans and P. reticulatum are needed in order not to lose further genetic variation. In addition, we confirmed that these markers are useful for the management of pure stocks in natural environments, for fish breeding, and in genetic conservation and improvement programs for these species.

Parasitological assessment in the hybrid surubim (Pseudoplatystoma reticulatum x P. corruscans), with uncommon occurrence of Monogenea parasites.

This study evaluated the parasite fauna of farmed hybrid surubim (Pseudoplatystoma reticulatum x P. corruscans) and the host-parasite-environment relationship in two fish farms located in Mato Grosso do Sul, Central Brazil, South America. A total of 120 hybrids from two different farms, 60 in each season (30 in the hot and 30 in cold season) were examined during a year. Water quality was weekly measured to evaluate the interaction among environmental conditions and parasitism. Histopathology was used to observe the effects of the parasites and environment on the fish gills. The ciliate protozoan Ichthyophthirius multifiliis and the monogeneans (Ameloblastella sp., Amphocleithrium paraguayensis, Vancleaveus ciccinus, V. fungulus and V. janacauensis) were the most prevalent parasites detected in both seasons in both farms, with prevalence above 80%. It was stated that parasites did not cause important damage in the health status of the hybrid surubim. These results might be related to general good management practices and environmental quality implemented by the fish farmers. The presence of uncommon monogenean parasites to this hybrid compared to their parents causing an environmental and ecological concern is here discussed.

Host-parasite relationship during Epistylis sp. (Ciliophora: Epistylididae) infestation in farmed cichlid and pimelodid fish

Abstract: The objective of this work was to describe the host-Epistylis sp. relationship during infestation on farmed fish. Five Nile tilapia (Oreochromis niloticus) and ten hybrid surubim catfish (Pseudoplatystoma reticulatum x P. corruscans), all diseased, were used for in vivo morphological analysis of sessile peritrichs by contrast microscopy. Fragments of infected tissues were subjected to histological processing and scanning electron microscopy. Epistylis sp. caused hemorrhagic ulcer disease, and cichlids were more prone to develop infestations throughout the body surface due to the attachment of the colonies to the scales, which did not occur with pimelodids. Multifocal granulomatous dermatitis was observed, associated with the hydropic degeneration of the epithelium and to ulcerative areas of necrosis. Microscopic examination showed the presence of bacterial microflora associated to Epistylis sp. peduncles. Therefore, this species can be considered a portal of entry for opportunistic bacteria.

Isolation of probiotic bacteria from the hybrid South American catfish Pseudoplatystoma reticulatum × Pseudoplatystoma corruscans (Siluriformes: Pimelodidae): A haematological approach

This study investigated bacterial strains with probiotic potential isolated from the middle portion of healthy hybrid surubim catfish foregut (Pseudoplatystoma reticulatum female×P. corruscans male). Twenty surubims weighing 1.5±0.3kg were used for bacterial isolation. In total, 41 strains of bacteria were selected in vitro. Ten strains had inhibition zones >10mm against Aeromonas hydrophila. Five of those strains presented inhibition zones >9mm against other pathogenic bacteria and reached concentrations greater than 105CFUmL−1 in tubes containing de Man, Rogosa and Sharpe (MRS) medium. In particular, Weissella cibaria (P36) reached 106CFUmL−1 in MRS and was able to reduce the pH of the medium to 3.85. In the in vivo intestinal colonization studies, 72 healthy hybrid surubims were fed with a commercial diet supplemented with probiotic W. cibaria for 15 days. Changes in gut community composition were then analyzed, and probiotic profile of W. cibaria was determined molecularly by amplification of rRNA 16S gene was performed using PCR. Compared to control fish, W. cibaria-supplemented fish showed an increase in RBC. These results show the efficacy of our haematological approach to probiotic screening in hybrid sorubim.

Symbiotic supplementation on the hemato-immunological parameters and survival of the hybrid surubim after challenge withAeromonas hydrophila

This study evaluated the effects of dietary supplementation with two symbiotics in the hybrid surubim (Pseudoplatystoma corruscans × P. reticulatum) prior to and after challenge with Aeromonas hydrophila. The fish were divided into unsupplemented fish, supplemented fish with Weissella cibaria and inulin, and supplemented fish with Lactobacillus plantarum and inulin. Twenty days after being fed symbiotics, the fish were sampled for immunological, haematological, and microbiological analysis pre-challenge. After this period, they were challenged with Aeromonas hydrophila, and after 96 h the fish were sampled for blood collection and survival. Fish fed W. cibaria and inulin from the pre-challenge showed the highest values of lysozyme activity. Fish fed L. plantarum and inulin presented a higher number of thrombocytes and granular leukocyte PAS+ than the other fish. After challenge, fish fed both symbiotics presented an increased red blood cells number. Fish fed L. plantarum and inulin showed an increased total leucocyte count (WBC), neutrophils, and monocytes number as well as total immunoglobulin. The W. cibaria- and inulin-supplemented fish showed improved haematological and immunological parameters and reduced cumulative mortality after the challenge.

Haematological Parameters of the Hybrid Surubim (Pseudoplatystoma reticulatum x P. corruscans) farmed in Brazil

This study evaluated the haematological parameters of the hybrid surubim (Pseudoplatystoma corruscans x P. reticulatum) farmed in intensive and semi intensive system. A total of 240 fish were examined, 120 from fish farm and 120 from a semi-intensive for comparison between the hot and cold season. The water quality was weekly measured to evaluate the influence of environmental conditions on the haematology. Fish from intensive system showed hematocrit and white blood cell count (WBC) higher in hot season while the total plasmatic protein, hemoglobin concentration, mean corpuscular hemoglobin concentration (MCHC) and mean corpuscular volume (MCV) were higher in cold season. In fish from semi intensive system, the red blood cells count (RBC) and total thrombocyte number was higher in hot season while the MCHC and MCV were higher in cold season. There was no alterations in the numbers of lymphocytes, neutrophils, basophils, eosinophils and PAS - positive granular leukocyte (PAS-LG). The results showed the influence of seasonality on the hematological parameters of the hybrid surubim kept under normal farming conditions. Regarding water quality, hot season was directly related to increased water temperature and decreased dissolved oxygen while the opposite was found in cold season.

Effects of the acute exposition to glyphosate-based herbicide on oxidative stress parameters and antioxidant responses in a hybrid Amazon fish surubim (Pseudoplatystoma sp)

The aim of this study was to investigate the effects of acute glyphosate (active ingredient) exposure on the oxidative stress biomarkers and antioxidant defenses of a hybrid surubim (Pseudoplatystoma sp). The fish were exposed to different herbicide concentrations for 96h. The thiobarbituric acid-reactive substances (TBARS), protein carbonyls and antioxidant responses were verified. The 15mg a.pL−1 of herbicide resulted in the death of 50% of the fish after 96h. An increase in liver and muscle TBARS levels was observed when fish were exposed to the herbicide. The protein carbonyl content was also increased in the liver (4.5mg a.pL−1 concentration) and brain (2.25mg a.pL−1 concentration). The antioxidant activities decreased in the liver and brain after exposure to herbicide. Levels of ascorbic acid in the liver (2.25mg a.pL−1 and 4.5mg a.pL−1 concentrations) and brain (2.25mg a.pL−1 concentration) were increased post-treatment. Levels of total thiols were increased in the liver and brain (2.25mg L−1 and 7.5mg a.pL−1, respectively). Glyphosate exposure, at the tested concentrations affects surubim health by promoting changes that can affect their survival in natural environment. Some parameters as TBARS and protein carbonyl could be early biomarkers for Roundup exposure in this fish species.

Evaluation of the Effects of Different Stunning Methods on the Stress Responses and Meat Quality of the Amazon hybrid surubim, Pseudoplatystoma fasciatum female × Leiarius marmoratus male

AbstractDifferent stunning methods (carbon dioxide [CO2] and hypothermia) used in industrial fish processing were compared with asphyxia in air, which is used in traditional fishing, to evaluate the effects of these methods on the stress responses and the meat quality of the Amazon hybrid surubim, Pseudoplatystoma fasciatum female × Leiarius marmoratus male. After the application, blood and behavioral indicators were evaluated. Following death by gill cutting, the fish were gutted, and analyses of muscle pH, rigor mortis, the exudation of the meat, and coloration were performed. Significantly higher levels of cortisol and glucose were exhibited by the fish subjected to asphyxia than by the fish stunned by either CO2 or hypothermia. The fish subjected to asphyxia displayed decreasing muscle pH during the first 2 h after death and showed higher rates of rigor mortis after 3 h than the fish that were stunned by the other two methods. The asphyxia is a practice that exposes fish to suffering by causing an increase in stress responses, which affects meat quality. The immersion of fish in water and ice (hypothermia) for 5 min was more effective stunning method than the use of CO2, resulting in higher loss of sensibility and greater welfare.

Vaccination strategies with oral booster for surubim hybrid (Pseudoplatystoma corruscans × P. reticulatum) against haemorrhagic septicaemia

Summary This study evaluated the efficiency of differently prepared vaccines against Aeromonas hydrophila in the hybrid surubim (Pseudoplatystoma corruscans × P. reticulatum). Survival and haemato-immunological parameters were compared between the treatments: non-vaccinated fish (C); bacterin-vaccinated fish (B); bacterin plus oral booster vaccinated fish (B+O); bacterin and toxoid-vaccinated fish (B+T) and bacterin, toxoid and oral booster-vaccinated fish (B+T+O). Fourteen-days vaccinated fish from B+O and B+T+O were fed with an oral booster for 4 days. After 1 week, the fish were intraperitoneally challenged with 2 × 108 CFU mL−1 of A. hydrophila. Fish from the treatment B+T+O showed the lowest cumulative mortality (11.36%) 96 h after challenge, compared with other treatments (22.72–44.04%), and a relative survival of 74%. Serum immunoglobulin in B+T+O fish was higher than in other treatments. All vaccinated fish showed an increased agglutination titre when compared with non-vaccinated fish, both before and after challenge. Fish fed with oral booster showed an increase in phagocytic percentage before and after challenge. It can be inferred that the oral booster vaccination was efficient in reducing mortality in hybrid surubim by enhancing the response against haemorrhagic septicaemia due to A. hydrophila infection.

Blood chemistry profile of Surubim hybrid fish (Pseudoplatystoma reticulatum X P. corruscans) raised in different stocking densities

Massive production, such as fish growing in water recirculation system, imposes challenges to animals capable of altering their homeostatic balance, and is able to affect their physiological performance. Therefore, the levels of ions and serum enzymes can be used as indicators of fish health. This study aimed to analyze the blood biochemistry profile of hybrid surubim (P. reticulatum X P. corruscans) submitted to different stocking densities in water recirculation system, in two distinct stages of production, from 150 to 400 g (first trial), and 400 to 1000 g (second trial). In the first trial, the five stocking rates were: 27.5, 47.5, 67.5, 87.5 and 107.5 fish/m³ of water. To obtain these densities, it was used 11, 19, 27, 35 and 43 fish per tank, respectively. In the second trial, five stocking rates were: 10, 20, 30, 40 and 50 fish/m³ of water. To obtain these densities we used 4, 8, 12, 16 and 20 fish per tank, respectively. The concentrations of glucose, cholesterol, triglycerides, urea, creatinine, alkaline phosphatase (ALP), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), calcium, phosphorus, potassium and magnesium were obtained. Only urea concentrations in first trial and ALP and AST concentrations in second trial were influenced by stocking density, presenting a significant difference between groups. Thus, in both trials the hybrid fish studied maintained homeostasis when reared in different stocking densities.

Feeding of larvae of the hybrid surubim Pseudoplatystoma sp. under two conditions of food management

We evaluated the growth and diet composition of hybrid surubim larvae (Pseudoplatystoma corruscans x P. reticulatum) produced in two fish farming by using different systems of feeding with natural plankton: M I, larvae are transferred to fertilized fish pond for being freely fed with natural plankton; M II, larvae are remained inside laboratory in glass fiber boxes and plankton are gathered with a plankton net and offered in a controlled way. It was collected 10 individuals daily during the feeding period with live plankton for 20 days. After the biometry, stomachs were opened and the food items identified and quantified by the volumetric method. The items were represented by algae, protozoa, microcrustacean, insect larvae and surubim fragments (cannibalism). The items with higher volumetric percentage were Chironomidae larvae (29.25%) followed by surubim fragments (19.68%) in M I, and surubim fragments (21.85%) and Moina micrura (19.97%) in MII. The items Chydorus sp., Diaphanosoma sp., sp. Macrothrix and Ephemeroptera larvae were found only in fish of M I, while algae Ulothrix sp., Oscillatoria sp. and the protozoa Difflugia sp were only found in stomachs of surubim from M II. Regarding the growth, the surubim had grown faster in M I.

Immunization of hybrid surubim (Pseudoplatystoma corruscans x P. fasciatum) against Motile Aeromonas hydrophila septicemia

The aim of this study was to evaluate the immune response of hybrid surubim vaccinated by intraperitoneal injection and by immersion against Aeromonas hydrophila. Vaccine was prepared with formalin-inactivated A. hydrophila. Forty eight fishes (47±9g) were distributed in 12 tanks (4 fish / tank) in the following treatments (4 tanks / treatment): unvaccinated fish, vaccinated intraperitoneally and vaccinated by immersion. After 21 days, intraperitoneally vaccinated fishes showed the highest values of total protein and immunoglobulins, agglutination titer and serum antimicrobial activity. Lysozyme concentration in the serum was higher in the fishes vaccinated by immersion than unvaccinated fishes. Intraperitoneal vaccination induced the highest immune response and could be used to improve the fish resistance against motile Aeromonas.

Brazilian catfish parasitized by Epistylis sp. (Ciliophora, Epistylididae), with description of parasite intensity score

The determination of mean intensity of parasitism for colony-forming sessile protozoan such as Epistylis has been a great problem in parasitological studies. Some alternatives have been proposed by researchers for laboratory and field conditions. This study describes the criteria to establish the parasitic intensity score for epistylidid infestation in fish. Parasite distribution and the host-parasite relationship in four species of Brazilian cultured catfish and their hybrids are discussed. The highest prevalence rates were found in the hybrid jundiara, Leiarius marmoratus male × Pseudoplatystoma reticulatum female (96.4%), followed by jurupoca, Hemisorubim platyrhynchos (60%), and the hybrid surubim, Pseudoplatystoma corruscans male × P. reticulatum female (52.7%). Positive correlation between parasitic intensity score and the fish size, weight, and relative condition factor were also observed. These findings indicate that Epistylis infestation in Brazilian catfish is an emerging disease in cultured fish.

Haemorrhagic septicaemia in the hybrid surubim (Pseudoplatystoma corruscans×Pseudoplatystoma fasciatum) caused by Aeromonas hydrophila

Intensive culture of the hybrid surubim (Pseudoplatystoma corruscans × Pseudoplatystoma fasciatum) in Brazil is responsible for the occurrence of diseases and consequent economic losses. However, the causative agents are not well known. The objective of this study was to isolate and to characterize the pathogenic agent responsible for mortalities in cultured surubim and to demonstrate its virulence. Ten fish from a fish farm located in the Mato Grosso do Sul State (Brazil) were collected and 14 haemolytic bacteria characterized as Aeromonas hydrophila were isolated from the kidneys (eight) and brain (six). As an experimental challenge, fish weighing 98.1±23.6 g were injected with 1 mL of saline solution and 2 × 102, 2 × 104, 2 × 106 and 2 × 108 CFU A. hydrophila mL−1. Fish infected with 2 × 108 CFU showed increased external and internal symptoms and mortality of 50±12.5% after 96 h. Increased A. hydrophila concentration was responsible for a decrease in haematocrit percentage and erythrocyte number, lymphocytes and eosinophils, as well as an increase in monocytes, neutrophils, serum agglutination titre and serum antimicrobial activity. It was concluded that A. hydrophila was responsible for characteristic symptoms of bacterial haemorrhagic septicaemia as well as important haematological and immunological alterations, which led to surubim mortality.