Nanoemulsions with oleoresin of Copaifera reticulata (Leguminosae) improve anthelmintic efficacy in the control of monogenean parasites when compared to oleoresin without nanoformulation

This study compared the in vitro anthelmintic activity of Copaifera reticulata oleoresin (200, 400, 600, 800 and 1,000 mg/L) and of nanoemulsions prepared with this oleoresin (50, 100, 150, 200 and 250 mg/L) against monogeneans on the gills of Colossoma macropomum. The major compounds present in the oleoresin of C. reticulata were γ-macrocarpene (14.2%), α-bergamotene (13.6%), β-selinene (13.4%) and β-caryophyllene (11.7%). All concentrations of the nanoemulsion and the oleoresin without nanoformulation showed anthelmintic efficacy against monogeneans, and higher concentrations led to more rapid parasite mortality. Structural damages to the tegument of the parasites exposed to C. reticulata oleoresin were observed with scanning electron microscopy. At two hours of exposure, fish showed 100% tolerance to all nanoemulsion concentrations used in the in vitro assays, whereas 100% mortality was shown in the fish exposed to the oleoresin without nanoformulation after one hour. The results of this study suggest that nanoemulsions with oleoresin of C. reticulata have advantages in the control and treatment of monogenean infections in C. macropomum when compared to the oleoresin without nanoformulation. In addition, since nanoemulsions with the C. reticulata oleoresin are safe to control monogeneans, the efficacy of these nanoformulations may be assayed in therapeutic baths to treat C. macropomum infected by monogeneans.     

Nanoemulsion from essential oil of Pterodon emarginatus (Fabaceae) shows in vitro efficacy against monogeneans of Colossoma macropomum (Pisces: Serrasalmidae)

Outbreaks of diseases pose a major threat to sustainable aquaculture development worldwide. Application of herbal products to combat parasitic diseases provides an alternative approach for sustainable aquaculture. This study investigated the in vitro antiparasitic effects of an oil‐in‐water nanoemulsion prepared using the essential oil from Pterodon emarginatus, against monogeneans infesting Colossoma macropomum. Gill arches from C. macropomum (47.6 ± 14.5 g and 13.5 ± 1.4 cm) that were naturally parasitized by Anacanthorus spathulatus, Notozothecium janauachensis and Mymarothecium boegeri were immersed in different dispersions of the P. emarginatus nanoemulsions (0, 50, 100, 200, 400 and 600 mg/L). The major compounds presented in the essential oil of P. emarginatus were β‐elemene, β‐caryophyllene and α‐humulene. Characterization of these nanoemulsions showed that they have a small mean droplet size and low polydispersity index, which is concordant with stable systems. In this in vitro trial, the P. emarginatus nanoemulsion concentrations of 100, 200, 400 and 600 mg/L presented 100% helminthic efficacy against monogeneans of the gills of C. macropomum. The highest two concentrations used (400 and 600 mg/L) were seen to immobilize the parasites after only 15 min. Therefore, it would be worthwhile testing these concentrations in therapeutic baths against monogeneans of C. macropomum.     

Essential oil of Lippia grata (Verbenaceae) is effective in the control of monogenean infections in Colossoma macropomum gills,a large Serrasalmidae fish from Amazon

This study investigated the efficacy of Lippia grata essential oil (EO) against monogeneans of Colossoma macropomum and effects on the haematology after immersion baths. In the in vitro assays, the efficacy of 100, 250, 350 and 700 mg/L of L. grata EO and two controls were tested, of which one control was with the cultivation tank water and the other was with the tank water and 70% ethyl alcohol. Composition of majority bioactive compounds in the EO was carvacrol (48.12%), p‐cymene (24.39%) and γ‐terpinene (2.49%). Anacanthorus spathulatus, Notozothecium janauachensis, Mymarothecium boegeri and Linguadactyloides brinkmanni obtained of fish gills showed 100% immobilization in the in vitro assays when exposed to 700 and 350 mg/L after 30 min and 2 hr respectively. Fish showed tolerance to 700 mg/L of the EO, which was used in therapeutic in three consecutive baths, which caused lamellar hyperplasia in C. macropomum gills. The 700 mg/L of the EO in the therapeutic baths showed an efficacy of 95.1% against the monogeneans and caused decrease in haemoglobin, whereas control fish showed a reduction in mean corpuscular haemoglobin concentration. Results indicated that 700 mg/L of L. grata EO is a safe and effective concentration to treat C. macropomum infected with monogeneans.     

Finishing plant diet supplemented with microalgae meal increases the docosahexaenoic acid content in Colossoma macropomum flesh

The need for a sustainable aquaculture is increasing the use of plant ingredients in replacement to fishmeal and fish oil in diets for tambaqui Colossoma macropomum, which is leading to not detectable levels of docosahexaenoic acid (DHA) in its flesh. We evaluated the effect of a finishing plant diet supplemented with 5% of microalgae meal from Schizochytrium sp. (MD) on tambaqui growth, on proximal composition and fatty acid content of its flesh, comparing it to a non‐supplemented diet. One hundred and sixty‐two fish (489.67 g) were distributed into six tanks (2,000 L) and fed the experimental diets for a 90‐day period. Three fish per tank were euthanized for analyses every 15 days. The MD did not affect the growth and proximal composition of fish flesh. The MD increased the DHA content (from 14.81 to 38.60 mg/g of lipids) and the n‐3:n‐6 ratio (from 0.16 to 0.51) in the flesh of fish, beginning on the 15th day and reaching the highest DHA content on the 71st day (39.81 mg/g of lipids). We recommend C. macropomum to be fed with a finishing diet supplemented with microalgae meal for 71 days before slaughter to improve the DHA content and n‐3:n‐6 ratio in the flesh.     

Effects of fisheries zoning and environmental characteristics on population parameters of the tambaqui (Colossoma macropomum) in managed floodplain lakes in the Central Amazon

Fisheries zoning and the influence of biotic and abiotic factors in the spatial distribution of Colossoma macropomum (Cuvier) in the Piagaçu‐Purus Sustainable Development Reserve, Central Amazon, during 2012–2013 were evaluated. The relative abundance and population parameters of the C. macropomum were compared between conservation (no‐take zone) and fishing (open to fishing zone) lakes. The fish were collected by experimental fishing in 2012 and 2013. A total of 296 individuals were captured, most of which were from the conservation lakes (62.8%). Higher proportions of larger adults and individuals were found in the conservation lakes, although no significant difference in the average C. macropomum catch‐per‐unit‐effort was found between the lake categories. Abundance was positively influenced by zooplankton density (r² = 0.53, P < 0.03). Therefore, it is hypothesised that conservation lakes may serve as refugia for juveniles due to the high availability of planktonic food available during the dry season. Although there were environmental differences between the two lake types, the relative success of management models that use no‐take zones in freshwater habitats was highlighted. Finally, the importance of zooplankton as a factor in the distribution of C. macropomum among floodplain lakes was emphasised.     

Acute lion's mane jellyfish,Cyanea capillata (Cnideria: Scyphozoa), exposure to Atlantic salmon (Salmo salar L.)

Jellyfish‐induced gill pathology relies upon occasional diagnostic observations yet the extent and impact of jellyfish blooms on aquaculture may be significant. Idiopathic gill lesions are often observed in apparently healthy fish. This study exposed Atlantic salmon (Salmo salar L.) smolts to macerated Cyanea capillata at 2.5 and 5 g/L for 2 hr under controlled laboratory conditions. Blood chemistry and gill histopathology were examined over a subsequent 4‐week period. Fish showed an acute response to the presence of jellyfish, including characteristic external “whiplash” discoloration of the skin and acute increases in blood electrolytes and CO₂ concentration; however, these were resolved within 4 days after exposure. Histopathologically, gills showed first an acute oedema with epithelial separation followed by focal haemorrhage and thrombus formation, and then progressive inflammatory epithelial hyperplasia that progressively resolved over the 4 weeks post‐exposure. Results were consistent with the envenomation of gills with cytotoxic neurotoxins and haemolysins known to be produced by C. capillata. This study suggests that many focal hyperplastic lesions on gills, especially those involving focal thrombi, may be the result of jellyfish stings. Thus, the presence of jellyfish and their impact may be severe and understated in terms of marine fish aquaculture and fish welfare.     

Albendazole,levamisole and ivermectin are effective against monogeneans of Colossoma macropomum (Pisces: Serrasalmidae)

This study evaluated the efficacy of albendazole, ivermectin, levamisole, mebendazole and praziquantel on monogeneans of Colossoma macropomum, based on in vitro and in vivo assays. In vitro assays indicated that albendazole (500, 100, 1,500 and 2,000 mg/L), ivermectin (200, 250, 300 and 350 mg/L) and levamisole (50, 75, 100 and 125 mg/L) were 100% effective against Anacanthorus spatulatus, Notozothecium janauachensis, Mymarothecium boegeri and Linguadactyloides brinkmanni, while mebendazole (125, 150, 175 and 200 mg/L) and praziquantel (5, 10, 15 and 20 mg/L) were ineffective. Fish mortality in 24 hr therapeutic baths with 500 mg/L of albendazole was 6.6%, but the behaviour of the animals remained unchanged, while 200 mg/L of ivermectin caused lethargy, signs of hypoxia and 100% mortality within 2 hr, and 125 mg/L of levamisole caused no mortality. The efficacy of 500 mg/L of albendazole was 48.6% in the 24 hr baths, while that of 125 mg/L levamisole was 88.2%. Although ivermectin showed in vitro efficacy, the lowest concentration used in baths was highly toxic to fish. Therefore, we recommend the use of 125 mg/L of levamisole to control and treat monogenean infestations on C. macropomum in fish farming.     

Geometric approach to evaluate the energy/protein balance in tambaqui (Colossoma macropomum): Can fish ensure nutritional intake targets by postingestion signals?

The aim of this study was to investigate the ability of tambaqui (Colossoma macropomum) to balance the energy (E) and protein (P) ratio by encapsulated diets (without sensory properties). Thirty fish (71.37 ± 2.58 g) were distributed in six 250‐litre tanks. Protein (P), carbohydrate (C) and fat (F) were encapsulated separately to ensure the same sensory properties of each macronutrient. Diets varied in terms of macronutrients to allow the maximal/minimal possibility of ingesting each nutrient following a geometric approach. P, C and F capsules were provided for 40 days (phase 1). After this procedure, fish were subjected to fixed low and poor protein challenges (200 g/kg), and freely to C + F, to evaluate whether they maintained a given intake target (phase 2). As a result, tambaqui showed an intake target at 300 g/kg of crude protein and 16.74 MJ per kg. Give the possibility of freely feeding protein, fish regulated their feed intake and showed a constant E/P ratio pattern (5.024‐5.861 MJ/kg). When protein was restricted and fixed at 200 g/kg, fish maintained similar feed consumption until the end of phase 1, probably to keep a minimal protein amount according to their nutritional requirements.     

Population dynamics and stock assessment of Colossoma macropomum caught in the Manacapuru Lake system (Amazon Basin,Brazil)

Colossoma macropomum is the second largest scaled fish in the Amazon basin. Reduced harvests in recent decades suggest that populations of this species are already overexploited in some areas. In this study, the population dynamics of C. macropomum was investigated using length and weight data for fish caught in the Manacapuru Lake system, a large ria lake located along the lower reach of the Solimões River. A total of 1270 individuals of C. macropomum with standard lengths varying from 17 to 62 cm and mean length of 31.0 ± 6.7 cm were sampled. Weights varied from 165 to 8195 g, and mean weight was 1148.3 ± 883.8 g. Maximum sustainable yield was estimated at 285.8 g recruit⁻¹, corresponding to a fishing mortality of 0.51 year⁻¹. A scenario analysis based on changes in fishing mortality and age at first capture, two parameters potentially addressed by fishing management strategies, suggested that any improvement in fishing yield depends on increases in age at first capture.     

Effect of low salinity on the expression profile of Na+/K+‐ATPase and the growth of juvenile chub mackerel (Scomber japonicus Houttuyn)

Chub mackerel (Scomber japonicus Houttuyn) is one of the most commercially important scombroid fish used as a food resource. Recently, there has been a demand for efficient rearing methods of this fish for a full‐life cycle aquaculture. In the present study, we evaluated the physiological responses in the juvenile S. japonicus to different ambient salinities. A significantly higher gain of the body mass was observed in the juveniles reared in 24 g/L and 13 g/L seawater than in those reared in natural seawater (34 g/L) within 40 days of the experimental period without affecting mortality. A principal enzyme for osmoregulation, Na⁺/K⁺‐ATPase, was expressed in the ionocytes located in the gill filaments of the juveniles. The number and the cell size of ionocytes and the enzymatic activity of Na⁺/K⁺‐ATPase in the gills decreased within 10 days after the low‐salinity challenge, which implies the reduction of the energy‐consuming active ion secretion under the low‐salinity environment. The physiological capacity for adaptation to low‐salinity seawater in chub mackerel could be basic knowledge to carry out culturing of these fish in coastal sea pens where ambient salinity fluctuates. The improvement of the growth performance by rearing in low‐salinity seawater will contribute to the efficient production of the seed juveniles for aquaculture.     

Winter kill in intensively stocked channel catfish (Ictalurus punctatus): Coinfection with Aeromonas veronii,Streptococcus parauberis and Shewanella putrefaciens

Unusual persistent natural mortality occurred in a floating in‐pond raceway system intensively stocked with channel and hybrid catfish beginning in early November 2016 up until March 2017. The temperature during the period of outbreak ranged from 7.2 to 23.7°C. Gross examination of freshly dead and moribund fish revealed pale gills, slight abdominal distension and swollen inflamed vents. Comprehensive necropsy of 20 fish demonstrated vast amounts of bloody ascitic fluid in the coelomic cavity, visceral congestion, splenomegaly and pale friable livers but macroscopically normal kidneys, suggesting systemic bacterial infection. Bacterial cultures were initiated from skin, gills and major internal organs. Following incubation, a mixture of three bacterial colony phenotypes was observed on agar plates. Presumptive biochemical characterization of the isolates followed by 16S‐rRNA sequence analysis resulted in the identification of Aeromonas veronii, Streptococcus parauberis and Shewanella putrefaciens. Channel catfish juveniles were experimentally infected with the recovered isolates to fulfil Koch's postulates. Moreover, an antibiogram was used to evaluate the susceptibility of the isolates to antimicrobial drugs approved for use in aquaculture. Aquaflor was used successfully for treatment. Here, we report bacterial coinfection lead by A. veronii and the first identification of S. parauberis and S. putrefaciens from cultured catfish in North America.     

Effects of iodized salt on the histopathology of the gills and liver in Rhamdia quelen and Metynnis maculatus

Table salt has been used as a reference substance in toxicological studies on fish and as an antiparasitic agent in aquaculture. The objectives of this work were to evaluate the sensitivity of Rhamdia quelen and Metynnis maculatus to iodized salt and to assess the possible changes in the gills and liver resulting from subchronic exposure of fish to this compound. The iodized salt toxicity levels after 96 h of exposure were 11.4 and 10.8 g L^?1 for R. quelen and M. maculatus. None of the observed changes in the livers of the studied fish could be unequivocally correlated with salt exposure. In turn, it could not be entirely ruled out that the changes found in the gills, including epithelial lifting, oedema formation and vascular congestion, were caused by exposure of fish to salt.     

Effect of 17β‐oestradiol on the sex ratio of tambaqui,Colossoma macropomum

The tambaqui Colossoma macropomum is the most important native fish in Brazilian aquaculture. Females are almost 20% heavier than males and therefore are more profitable. Based on this information, we tested four different concentrations (20, 40, 80, and 120 mg/kg diet) of oestradiol (E₂) offered during 6 weeks to tambaqui larvae and analysed their efficiency in producing female monosex batches of the species. The study was performed in two independent tests, using different genetic backgrounds (broodstocks). All treatments increased the percentage of females in the population, but only the highest E₂ dose was “free” of males in both tests. All treated groups contained intersex individuals (when sex inversion is not complete). Plasmatic E₂ concentration was similar between treated and non‐treated fish 60 days after the treatment in fish treated with 20, 40, and 80 mg E₂/kg diet. However, tambaqui treated with a 120 mg E₂/kg diet showed lower E₂ plasma concentration in comparison with the control group. Last, we chlorinated the water to ensure the environmental integrity of the study. Three days after chlorination, the water was completely free of any oestradiol residue (analysed by high‐performance liquid chromatography).     

Assessment of induction and recovery times of anaesthesia in Astyanax bimaculatus using 2‐phenoxyethanol and the essential oils of Melaleuca alternifolia and Ocimum gratissimum

This study aimed to determine the lowest effective concentration (LEC) of 2‐phenoxyethanol (2‐Phe) and essential oils (EOs) of Melaleuca alternifolia and Ocimum gratissimum able to induce anaesthesia in Astyanax bimaculatus. LEC was assumed to be the required concentration to carry out anaesthesia in less than 3 min with recovery in <5 min and sufficient to carry out routine aquaculture procedures. The following concentrations were tested: 2‐Phe (100, 200, 300, 400, 500 and 600 µl/L); M. alternifolia (200, 300, 400, 500 and 600 µl/L); and O. gratissimum (10, 20, 30, 40, 50, 60, 70, 100, 150, 250 and 300 µl/L). Results show that all three agents evaluated have effective anaesthetic properties for use in Astyanax bimaculatus with LEC for 2‐Phe, M. alternifolia and O. gratissimum of 200, 300 and 60 µl/L respectively.     

Efficacy of bath vaccination with a live attenuated Vibrio harveyi against vibriosis in Asian seabass fingerling,Lates calcarifer

Vibrio harveyi causes vibriosis in various marine aquaculture fish species, especially when they are young. The infection subsequently leads to significant economic losses for aquaculture farms. Vaccination is recommended to control this disease. This study describes the efficacy of a live attenuated V. harveyi strain MVh_vhs (LAVh) as a vaccine candidate in controlling infection by wild‐type V. harveyi (WTVh) in Lates calcarifer. A total of 240 fingerlings were divided into four groups. Group 1 was not vaccinated and was not challenged, Group 2 was vaccinated with a formalin‐killed V. harveyi (FKVh), Group 3 was vaccinated with the LAVh before challenge and Group 4 was not vaccinated and was challenged. Bath vaccination was employed for one hour before the LAVh distribution was determined in the fish mucus, gill, liver, gut, kidney and spleen. The gills, livers, kidneys and skins were also sampled for gene expression analysis. To challenge the fish, skin abrasion was conducted before the fish were challenged by immersion with WTVh. The results revealed an extensive distribution of the LAVh in the liver and kidneys of the fish in Group 3 for the first 12 hr, resulting in mild lesions compared with Group 1. Similarly, there were significantly (p < .05) higher expressions of the Chemokine ligand 4 and major histocompatibility complex I genes in the skin and liver of the fish in Group 3 in comparison with other groups. Vaccination with LAVh resulted in a significantly high rate of survival (68%) of the fingerlings after being challenged with WTVh.     

Effects of astaxanthin on Brachionus manjavacas (Rotifera) population growth

Astaxanthin is a red secondary carotenoid and powerful antioxidant that is used in aquaculture to enhance colour and improve fish health. Brachionid rotifers are often used as a live feed for larval fish, but do not contain endogenous carotenoids. However, they can be enriched with astaxanthin through their diet and transfer it to larval predators. When supplemented with 2 μg/ml astaxanthin oleoresin extracted from the green alga Haematococcus pluvialis, Brachionus manjavacas rotifer cultures reached significantly higher population densities and maintained them for longer. Furthermore, data are presented that exposure to oleoresin or pure astaxanthin enhances rotifer resistance to oxidative stress, a common cause for the collapse of rotifer mass cultures. Astaxanthin can be visualized in the gut of the rotifers, allowing the time course of uptake to be estimated by image analysis. Using this method, it was found that accumulation of astaxanthin in the rotifer gut saturates after 1.5 hr of exposure. The bioactive dose of astaxanthin oleoresin for rotifers was found to be 1–20 μg/ml. Astaxanthin concentration in rotifer tissues was measured using absorbance spectrophotometry. It was found that treating rotifers with 20 μg/ml for 24 hr; the concentration of astaxanthin absorbed into rotifer tissues was 2.6 mg/g. Overall, these experiments indicate that astaxanthin extracted from H. pluvialis can be used to improve the productivity and stability of rotifer mass cultures by increasing oxidative stress resistance and enhance the nutritional content of rotifers for larval fish.     

Fish meal replacement by soy protein from soymilk in the diets of red sea bream (Pagrus major)

Six isoenergetic diets were formulated as follows: fish meal (FM) 700 g kg^–1 (control, C), FM 300 g kg^–1 + soy protein concentrate 300 g kg^–1 (SPC), FM 300 g kg^–1 + enzyme‐treated SPC 300 g kg^–1 (ESC), FM 170 g kg^–1 + soy protein isolate 300 g kg^–1 (SPI), FM 160 g kg^–1 + enzyme‐treated SPI 300 g kg^–1 (ESI) and FM 150 g kg^–1 + conglycinin 300 g kg^–1(CG). Forty fish (3.9 g) were randomly distributed into each of eighteen 300‐L tanks, fed twice daily until satiation for 8 weeks. The final body weight, specific growth rate and condition factor did not show significant differences among the fish fed with diets C, SPC, ESC and ESI (p > .05). The survival was significantly lower in fish fed with diets SPI and CG. Feed efficiency was significantly higher in fish fed with diets SPC and C than in fish fed with other diets (p < .05). There were no significant differences in nutrients retention efficiencies in fish fed with diets C, SPC, ESC and ESI. A significantly higher phosphorus retention efficiency in fish fed with soymilk protein diets resulted in lower phosphorus discharge to the environment (p < .05). These results suggest that the soymilk proteins can comfortably replace 570–770 g FM kg^–1 diet of red sea bream juvenile, which will ensure significant ecological benefits through reducing phosphorus load to the environment.     

First record of infection by Trypanosoma sp. of Colossoma macropomum (Serrasalmidae), a neotropical fish cultivated in the Brazilian Amazon

Fish farming has grown rapidly in Brazil over the last two decades, due in part to the availability of water and species with potential for cultivation, such as Colossoma macropomum. This farmed fish, however, can be affected by parasitic infections with high mortality rates (>35%). The main objective of the present study was to describe the first occurrence of the Trypanosoma species in Colossoma macropomum, which occurred in fish cultured in the Brazilian Amazon region, as well as to morphologically characterize the trypomastigotes and the impact of these hemoparasites on the body condition of the hosts. The trypanosomes found in the blood of Colossoma macropomum were morphologically characterized by the size of the trypomastigote form, indicating the presence of only one morphotype. Of the 39 hosts examined from one fish farming, 41.0% were infected by Trypanosoma sp., with low levels of infection (mean blood density of 3.7/μL). The condition factor of the asymptomatic hosts was not affected by hemoparasitism. There was no correlation between the abundance of Trypanosoma sp. and the condition factor and size of the hosts. Finally, our understanding of host-parasite interactions and the detection of emerging diseases are fundamental for aquaculture.     

Dietary supplementation with autochthonous Bacillus cereus improves growth performance and survival in tambaqui Colossoma macropomum

The aim of this study was to evaluate the effect of dietary supplementation with the autochthonous probiotic bacteria Bacillus cereus on growth performance, haematological parameters and survival of tambaqui (Colossoma macropomum). Tambaqui fingerlings (0.94 ± 0.02 g) were fed for 120 days the following diets: basal (without probiotic) and three supplemented diets (4.2 × 10⁴, 3.9 × 10⁶ and 3.3 × 10⁸ CFU/g). Growth performance and haematological parameters were evaluated every 30 days. Thereafter, fish were challenged against Aeromonas hydrophila and survival was evaluated. Probiotic B. cereus improved weight and length gains (p < 0.05), and increased neutrophils and thrombocyte counts (p < 0.05) in tambaqui supplemented with 3.9 × 10⁶ CFU/g diet. Challenged fish fed unsupplemented diet presented the lowest survival rate (33.4%) while fish fed diets supplemented at 4.2 × 10⁴, 3.9 × 10⁶ and 3.3 × 10⁸ CFU/g B. cereus had 88.8%, 80.5% and 80.5% relative per cent survival respectively. These results demonstrated that B. cereus supplemented as probiotics to C. macropomum for 120 days improved physiological and haematological responses, leading to enhanced survival in this fish species.