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The current study investigates the preparation, purification, and identification of novel antioxidant peptides from Piaractus brachypomus fish (RBPF) meat. Antioxidant peptides from RBPF meat protein hydrolysate (RPMPH) were fractionated by ultrafiltration (3 kDa MWCO membrane). RPMPH-IF (MW < 3 kDa) fraction displayed significantly higher antioxidant activities ( P  < 0.05) (DPPH, ABTS, FRAP, and Fe 2+ chelating activity). RPMPH-IF was purified by Sephadex G-25 gel filtration chromatography, and the RPMPH-1 fraction exhibited significantly higher antioxidant activities ( P  < 0.05). Subsequently, the RPMPH-1 fraction was purified by reversed-phase high-performance liquid chromatography. RPH-8 showed the highest antioxidant activities. The sequence of peptides of the RPH-8 fraction was later identified by LC-MS/MS and MASCOT software. RPH-8 fraction showed the two peptides with MW of 1105.52 Da and 748.25 Da, and the sequence of peptides was identified as His–Asn–Leu–Gly–Leu–Leu–His–Gly–Asp–Met and Asp–Ala–Pro–Ser–Met–Asn–Asp, respectively. Thus, RPMPH or purified antioxidant peptides produced by probiotic Bacillus strain could be a bio-functional ingredient in food and nutraceutical applications.

The transfer of live fish from production facilities to processing plants imposes significant stress on the animals, with negative impacts on fillet quality. Considering the numerous species of fish that exist, research into pre-slaughter handling and processing strategies that can have a beneficial impact on fillet quality can generate profitability for the production sector and a higher quality product for the consumer. This study aimed to investigate the influence of varying post-transport rest times on muscle glycogen, blood glucose and meat quality characteristics in the pre- and post-rigor mortis stages of patinga. An experiment was conducted in a 4 × 2 factorial design, with four transport recovery times (0, 2, 4 and 6 hours) and two processing phases (pre- and post-rigor mortis). Muscle glycogen levels showed an increase, accompanied by a decline in blood glucose, as rest times extended, with homeostasis being restored after 6 hours of rest. Fish processed in pre-rigor mortis after 6 hours of rest had fillets with greater luminosity, lower red intensity and greater firmness. Six hours of rest resulted in fillets with lower weight loss due to cooking and higher water holding capacity (WHC). Filleting post-rigor mortis resulted in fillets with lower cooking loss, lower luminosity, lower yellow intensity and higher WHC. Therefore, resting post-transport for 6 hours is effective for recovering from stress and has a positive impact on fillet quality. Processing patingas post-rigor mortis provides fillets with lower weight loss and better coloring.

Frugivory and seed dispersal by fish is an important mutualistic interaction in complex and species-rich tropical rivers. The local ecological knowledge (LEK) held by fishers can provide new information on relationships between fishes and plants in less studied rivers. This study aims to investigate the feeding interactions between frugivorous fish and plants through interaction networks based on the fishers' LEK in three rivers in the Brazilian Amazon (Negro, Tapajós and Tocantins). A total of 418 fishers were interviewed in 24 communities (eight in each river). The studied fishes were tambaqui (Colossoma macropomum), matrinxã (Brycon spp.), pacu (Myloplus spp.), pacu manteiga (Mylossoma duriventre), pirapitinga (Piaractus brachypomus), and jaraqui (Semaprochilodus spp.). The interviewed fishers cited a total of 92 plants consumed by the six frugivorous fishes in the three rivers. The interaction networks showed a higher nestedness in the Tocantins, greater connectance and modularity in the Tapajós and more specialization in the Negro, where the protected areas may have contributed to a more complex and specialized interaction network. The more nested network in the Tocantins River indicated the loss of specialized interactions in disturbed communities. The Tapajós River network showed the highest number of interactions between fish and plants, but this river has been threatened by environmental changes. Fishers' LEK associated to network analyses can advance our understanding on ecological interactions. This approach can be also useful to evaluate and mitigate ecological effects from anthropic changes in the Amazon and other high diverse tropical rivers.

Chronic exposure to high biofloc total suspended solids (TSS) could affect growth, red blood cells, and generate gill alterations in fish. Red pacu, Piaractus brachypomus, fry (2.7 ± 0.5 g weight) were exposed to different biofloc TSS concentrations with low (T1: 200–300), and medium (T2: 400–600 mg/L) levels and compared to a treatment control (TC) without solids during a 45‐day period in 50 L experimental units (in quadruplicate). Water quality, productive parameters, red blood cell values, and gill histopathological alteration index (HAI) were assessed. Red pacu reached higher final biomass (11.34 ± 0.73 kg/m3), better growth (DWG = 0.30 ± 0.03 g/day) and food conversion rate (1.05 ± 0.02) in TC than in biofloc treatments (p < .05). T2 had higher RBC count, and lower hemoglobin, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration (p < .05) than T1 and TC. The histological sections of TC gills showed monogenean parasites in low quantity; thus, the HAI value was similar among treatments and corresponded to low to medium gill damage. Growth, red blood cell values, and gill morphology of red pacu fingerlings were affected by moderate (400–600 mg/L) chronic exposure to TSS concentration in biofloc.

Mercury is a xenobiotic contaminant often found in natural ecosystems. It is relevant for public and environmental health because of the existing correlation between its content in water sources and mercury bioaccumulation in living organisms. This work assessed the immune and histopathological effects of exposure to sublethal concentrations of mercury chloride (HgCl^sub 2^) in Pacu. Pacu fingerlings weighing 10 g ± 2.1 g were distributed in constantly aerated tanks with no filter. A negative control group and four Hg levels were used based on the tenth of LC^sub 50^ for Pacu. Hepatosomatic index values showed no significant differences. Animals exposed to HgCl^sub 2^ showed low bactericidal activity of plasma. Histopathological changes such as hyperplasia, aneurysms and synechiae were found in gills, while hyaline inclusions were observed in liver and melanomacrophage centers in kidney. Pacu fingerlings exposed to sublethal doses of HgCl^sub 2^ had a significant increase in oxidative stress and changes in plasma bactericidal activity in addition to pathological changes in the gills, hepatic and renal tissues.

The practice of hybridization is carried out globally in fish farms. Here, we present the first record of the parasitic fauna of hybrids among genus Colossoma and Piaractus in natural environments. We identified a total of 48 hybrids, nine F1 hybrids (nuclear DNA from both species present in the cross) and 38 advanced hybrids (nuclear DNA from one species), both from crosses between Piaractus brachypomus and Piaractus mesopotamicus , and one F1 “tambacu” corresponding to cross between Colossoma macropomum and Piaractus mesopotamicus . This is the first record of Anacanthorus penilabiatus , Anacanthorus toledoensis , Mymarothecium viatorum , Mymarothecium ianwhittington , Haementeria sp., Dadaytrema oxycephala , Rondonia rondoni , and Echinorhynchus gomesi parasitizing hybrids collected in a natural environment. With this, we expand knowledge about the diversity of fish and parasites in the upper Paraná River and warn about the risk that fish escapes can cause in the basin.

Neurogranin (NRGN) is a small brain protein expressed in various telencephalic areas and plays an essential role in synaptic plasticity by regulating the availability of calmodulin (CaM). The study aims to characterize the neurogranin gene in Colombian native fish, red-bellied pacu, Piaractus brachypomus , its basal tissue expression and differential expression in brain injury and sublethal toxicity by organophosphates. NRGN gene contains an open reading frame of 183 nucleotides encoding for 60 amino acids. Bioinformatics analysis showed an IQ motif necessary in the interaction with CaM. NRGN mRNA was detected in tissues with higher expression in brain, gills, and head kidney. In brain regions, NRGN showed high expression in the telencephalon (TE) and olfactory bulb (OB). In the sublethal toxicity experiment, NRGN mRNA was upregulated in individuals under organophosphate exposure in the OB and optic chiasm (OC). In brain injury experiment, NRGN showed upregulation at 14 days in OC and at 24 h and 7 days in TE. These findings demonstrate the differential expression of NRGN under different experimental conditions which make it a candidate for a biomarker in the brain of P. brachypomus .

The improper disposal of mercury-containing substances may cause toxicity and accumulate in fish tissues. In this study, the median lethal concentration (LC50) of mercury exposure at 96 hours in cachama blanca [Piaractus brachypomus (Cuvier, 1818)] was estimated through a semi-static acute toxicity test by using mercury chloride (HgCl2) as a metal source. The experiment was carried out in the toxicology laboratory of the University of Tolima (Colombia), under controlled conditions (28.09 plus or minus 1.86 degree C) and a 12:12 (light:darkness) photoperiod. The cachama blanca fingerlings (6.55 plus or minus 1.3 g) were housed in glass aquaria with constant aeration without filter and feeding was suppressed 24 hours before beginning the experiment. Four cencnetrations of mercury (Hg) were used with replicas including controls. The concentrations were: 0.45, 0.55, 0.65, and 0.75 mg Hg/l. The value of LC50-96 h was estimated by using the TSK software (Trimmed-Spearman-Karber) and produced a value of 0.56 mg Hg/l. This value is close to those reported for other fish species and represents the first report of acute toxicity to the mercury in cachama blanca.

The effects of thermal shock on hematological, biochemical and antioxidant responses were evaluated in liver tissue of juvenile tambaqui (Colossoma macropomum) and tambatinga (♀ C. macropomum × ♂ Piaractus brachypomus). Forty juveniles of tambaqui and 40 juveniles of tambatinga, of the same age and with an initial weight of 23.3 ± 6.7 g, were randomly distributed in eight 28L circular tanks. A tank (n = 10 fish) of tambaqui and a tank (n = 10 fish) of tambatinga were then used to obtain basal data. The other animals were subjected to thermal shock with sudden temperature reduction from 28 to 18 ºC. Blood and tissue were then collected after 1, 6 and 24 h from the onset of thermal shock. No mortality was observed during the experimental period. Thermal shock increased triglyceride levels after 24 h of stress for tambaqui and reduced values for tambatinga. There was an effect on plasma glucose only for fish group (P < 0.0001) and collection time (P < 0.0001) with a peak observed for the hybrid after 6 h. The interaction of factors for SOD indicated greater activity for tambatinga at the 6 h collection and lower at basal and 1 h collections. There was an interaction for CAT (P = 0.0020) with less activity for tambatinga at 1 h. However, thermal shock and hybridization did not influence GST and TBARS levels in liver tissue. Therefore, the results suggest that the hybrid, tambatinga, is more efficient at promoting adjustments of biochemical responses and antioxidant enzymes during thermal shock.

Branchiura are a crustacean parasite widely known around the world as fish lice. In South America, they have been most studied in Brazil as with high levels of infestation, the parasites can be harmful to the health of fish and cause economic losses in fish farms. The objective of the present study is to provide, for the first time, significant information about the parasitic indices, infestation sites, and morphology of Dolops carvalhoi , and to report the appearance of a new host in the Amazon region of Peru. A total of 24 specimens of Colossoma macropomum , Piaractus brachypomus , and Calophysus macropterus from fish farms were individually analyzed to identify the presence of the ectoparasites. The Branchiura collected from the body surfaces of the fish were separated according to sex, the parasitic indices were calculated, and the parasites were clarified in 90% lactic acid for taxonomic identification. They were also preserved in 2.5% glutaraldehyde, and dehydration and critical point procedures were applied by scanning electron microscopy to visualize the detailed structures. The taxa identified was D. carvalhoi , which had a prevalence of 64.7%, a mean intensity of 1.6, and a mean abundance of 1 parasite/fish in C. macropterus ; a prevalence of 100%, a mean intensity, and mean abundance of 2.8 parasites/fish in P. brachypomus ; and a prevalence of 100%, but a mean intensity and mean abundance of 15 parasites/fish in C. macropomum . The pectoral and dorsal fins and the urogenital opening had the highest occurrence of D. carvalhoi in the host. Dolops carvalhoi has sexual dimorphism, and we reported for the first time the infestation of this parasite in leather fish C. macropterus .