Outbreaks of fish trypanosomiasis are regularly reported in cultured groupers (Epinephelus spp.), largemouth bass (Micropterus salmoides), and many other species of Cyprinidae, but only rarely reported in ornamental fish. This study reports a trypanosomiasis outbreak in farmed blood parrot cichlids (Vieja melanura♀ × Amphilophus citrinellus♂) in the Nansha district, Guangzhou, Guangdong province. From May 2021 to January 2022, up to 100 fish died daily with an estimated overall mortality of 20%. Blood samples were collected from 21 sick fish, characterized by reduced feeding, slow movement and swimming close to the surface of the water, and 5 asymptomatic fish for parasite examination. Wet blood mounts and Giemsa-stained smears showed that trypanosomes were found in 20 of 21 sick fish (95.2%) and 4 of 5 (80%) asymptomatic fish. Parasitemias were recorded at levels of up to approximately 108 trypanosomes /ml of blood. Morphological and genetic analysis showed that the trypanosome infecting blood parrot cichlids was Trypanosoma carassii danilewskyi. In addition, histopathological analysis showed a severe steatosis in liver and an aggregation of pigments in the spleen and kidneys, which are likely to be melanomacrophages. To our knowledge, this is the first report of an outbreak of trypanosomiasis found in farmed blood parrot cichlids.

The research examined the impact of adding potassium diformate (KDF) and sodium diformate (NDF) to the diet of Siberian sturgeon (Acipenser baerii) and how it influenced their antioxidant levels and immune responses. The fish (n = 315; 17.85 ± 0.2 g initial weight) were fed with seven diets for 56 days, including a control group (unsupplemented diet) and groups with varying levels of KDF (0.15, 0.3, and 0.5%) and NDF (0.15, 0.3, and 0.5%). After the feeding trial, the groups that consumed KDF or NDF demonstrated a dose-responsive elevation in serum superoxide dismutase, catalase, and glutathione peroxidase levels, along with an overall increase in total antioxidant capacity compared to the control group (P < 0.05). These groups also had lower malondialdehyde levels (P < 0.05) and improved immune functions, including higher levels of immunoglobulin M, total protein, albumin, globulin, the activities of lysozyme, respiratory burst, and alternative complement (P < 0.05). Also, the serum bactericidal activity experienced a significant increase (maximum in 0.5% NDF treatment) in the groups subjected to experimental feeding compared to the control group (P < 0.05). The transcription levels of interleukin-1 beta (IL-1β), interleukin 8 (IL-8), tumor necrosis factor-alpha (TNF-α), high mobility group box 1 (AbHMGB1), and high mobility group box 2 (AbHMGB2) genes in the head kidney were significantly upregulated in fish fed with different doses of KDF or NDF compared to the control group (P < 0.05). The most significant upregulation was observed in the group that received 0.5% NDF. Moreover, the experimental groups demonstrated a lower cumulative mortality rate of the fish following exposure to Aeromonas hydrophila AB005 infection compared to the control group (P < 0.05), with the lowest mortality rate observed in the 0.5% NDF or KDF group. Overall, the results suggest that dietary KDF or NDF, especially 0.5% NDF, are promising as environmentally friendly options and sustainable immunostimulants in Siberian sturgeon aquaculture.

Heterobothriosis resistance and high growth performance are major concerns in the tiger pufferfish (Takifugu rubripes) farming. Our previous small-scale study suggested the feasibility of genomic selection (GS) for these traits but also identified an undesired genetic correlation between them, which could hamper simultaneous genetic improvement. Here, we sought to validate these initial findings through larger samples and crosses and also explore the potential of GS for the individuals fed a normal fishmeal diet and a low fishmeal (LFM) diet. We produced three populations: one was fed a normal diet (PopFM: 1100 individuals) and two were fed an LFM diet (PopLFM1: 993 individuals; PopLFM2: 1017 individuals); all three populations were artificially infected with Heterobothrium okamotoi, a monogenean parasite causing heterobothriosis. We recorded standard lengths of the fish after artificial infection (SLEAI) and the number of parasites on the gill cavity wall (HC) and genotyped genome-wide single nucleotide polymorphisms (SNPs) using genotyping by random amplicon sequencing, direct (GRAS-Di) technology for each sample: PopFM, 12 K SNPs; PopLFM1, 19 K SNPs; PopLFM2, 21 K SNPs. Heritability and prediction ability for each trait were estimated for each population using genomic best linear unbiased prediction (GBLUP), Bayes C, and Bayesian ridge regression methods. SNP effects on each trait were estimated by Bayes C, Bayesian ridge regression, and genome-wide association analyses (GWAS) using the same data sets. We observed moderate to high levels of heritability for HC (0.16–0.57) and SLEAI (0.50–0.77), with predictive ability of 0.25–0.55 for HC and of 0.51–0.73 for SLEAI. These values were slightly larger in LFM diet groups. As reported previously, a weak undesired genetic correlation was observed between the traits, and the correlation was more pronounced in the LFM groups. In conclusion, our results indicate that genetic gain in growth and parasite resistance traits can be expected for the tiger pufferfish through GS, especially for individuals reared on an LFM diet. However, close attention should be paid to the extent of the undesirable genetic correlation between the two traits that may be amplified in the populations fed an LFM diet.

This study evaluated effects of nano‑selenium (nano-Se) on growth, feed utilization and antioxidant status of Catla catla fed isonitrogenous (26.25% protein) and isolipidic (13.12% lipid) diets formulated to contain nano-Se at 0, 0.75, 1.5 and 2.25 mg/kg (analysed Se 0.32, 1.08, 1.81 and 2.61 mg/kg). There were three tanks (89 × 58 × 61 cm) for each of the four feed treatments, and each tank of 25 fish (initial weight of 6.41 ± 0.02 g) was fed to satiation twice each day for 90 days. After 90 days, growth performance and survival rate were noted and then 9 fish from each replicate were harvested and analysed for body proximate composition, serum biochemistry and antioxidant enzyme activities. The remaining 16 fish from each replicate were subjected to temperature and hypoxia stress (8 fish against each stressor). Orthogonal polynomial contrast analysis revealed dietary nano-Se supplementation significantly improved the growth performance and feed utilization in linear, quadratic trends. Fish fed diet containing 1.08 mg/kg nano-Se showed highest weight gain (28.00 ± 0.84 g) and specific growth rate (1.87 ± 0.01%/day) and lowest FCR (1.07 ± 0.03). However, no significant effect was observed on the feed intake or survival rates of the fish. Furthermore, whole body moisture, crude protein (CP) and ash contents showed significant linear and quadratic trends in response to dietary nano-Se. Before and after stress challenges, significant increase in liver superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase activities (GPx) and decrease in thiobarbituric acid reactive substances (TBARS) were observed in fish fed 1.08 mg/kg nano-Se diets compared with the control group. Before stress, nano-Se supplementation had no effect on the levels of serum glucose (GLU), serum cortisol (CORT) or the survival rate (SR), however, significant elevations in these parameters were observed after stress challenges. Fish fed 1.08 mg/kg nano-Se diet showed significantly lower values of GLU, CORT and SR as compared to the control group after each stress challenge. In conclusion, nano-Se supplementation improved the growth performance, health status and response to stressor in Catla catla. The optimum nano-Se concentration in the diets of C. catla was estimated to be 1.54, 1.60, 1.58 and 1.64 mg/kg on the basis of weight gain percent, FCR, TBARS and GLU, respectively.

In this study, we produced a population of gynogenetic mrigal carp (Cirrhinus mrigala, GMCJ) through artificial gynogenesis using UV-inactivated white crucian carp spermatozoa. The GMCJ exhibited a faster growth rate and strong resistance to low temperatures, surviving natural winter conditions with temperatures below 10 °C. To gain a deeper insight into GMCJ's molecular response to acute cold stress (a decrease in water temperature from 26 °C to 14 °C within 1 h at a rate of 0.2 °C/min), we conducted a comparative analysis of the histology and transcriptomics of the brain-liver axis. Transmission electron microscopy of the heart tissues revealed that acute cold stress result in widened myofilament spacing, along with enlarged, deformed mitochondria that developed vacuoles and ruptured. We identified differentially expressed genes (DEGs) in the brain (2463 upregulated and 3288 downregulated genes) and liver (1210 upregulated and 1224 downregulated genes). Analysis of the DEGs' correlations indicated that major pathways involved in immunity, disease, metabolism, and growth were active and interconnected. KEGG functional analysis showed that the most enriched pathways in the brain-liver axis involved the regulation of the glucagon pathway, PI3K-Akt signaling pathway, and herpes simplex infection. Numerous genes associated with the nervous-endocrine system were activated, suggesting a coordinated response of the brain-liver axis to acute stress. These findings enhance our understanding of how farmed, particularly gynogenetic fish respond to acute cold stress.

Salinity tolerance is a complex trait of ecological and economic importance in tilapia aquaculture. To further dissect the genetic architecture underlying this trait, we performed a genome-wide association study (GWAS) using ddRAD-seq in an F1 tilapia population of GIFT tilapia, which is derived from selective breeding. Unlike previous studies localized to ∼23 Mb on chrLG18, we identified 11 novel genome-wide significant SNPs spanning a 4.6 Mb region (24,593,966 to 29,240,173 bp) on chrLG18 associated with salinity tolerance. GO enrichment analysis of the genes within this QTL region on chrLG18 showed significant enrichment of genes involved in fatty acid metabolism. The significant associations with salinity tolerance for the two missense mutations, LG18_25,305,119 (c.C388T) and LG18_25,305,122 (c.A391G), in the slc25a24l gene have been confirmed by Sanger sequencing. Individuals homozygotes for the T allele of LG18_25,305,119 and G allele of LG18_25,305,122 demonstrated over 2-fold longer average survival times under high salinity challenge compared to the individuals with disadvantageous genotypes. The mutated 131th amino acid (I/V) in SLC25A24L corresponding to the location of the nonsynonymous SNP LG18_25,305,122 showed a strong association with habitat salinity differences when comparing orthologs between freshwater and marine fish species. Our findings provide novel insights into QTLs, candidate genes and mutations conferring enhanced osmoregulatory capacity in tilapia.

Nile tilapia is a widely produced species due to its rusticity and technological culture package. However, there is a knowledge gap in youth production using new technologies. Therefore, this work aimed to evaluate the production of juvenile Oreochromis niloticus in different culture technologies: autotrophic, synbiotic, and bioflocs, through of water quality parameters, plankton groups, bacterial counts and zootechnical performance. The experiment lasted 40 days, time needed to reach a commercial weight of juveniles, and used tilápia fry weighing 3.60 ± 0.32 g stocking density of 500 fish m−3 and fed with commercial feed (46% crude protein and 9% lipids). Before stocking the fish, the experimental units were prepared for 30 days with inorganic (potassium nitrate and superphosphate - autotrophic - AUT) and organic (sugar - bioflocs - BFT; rice bran fermented with probiotic - synbiotic - SYNB) addition and control group (CTL). Regarding water quality parameters, temperature, salinity, dissolved oxygen (DO) and pH were within those recommended for the culture of the species. The nitrogen compounds (TAN and N-NO2) and water footprint were lower in BFT and SYNB as compared than AUT and CTL. The phytoplankton community had significantly higher Bacillariophyta count in BFT and SYNB as compared than AUT and CLT, however Chlorophyta in AUT and Cyanophyta in BFT, SYNB and CTL, prevailed. Zooplankton showed dominance of Rotifera in all treatments, with higher values in SYNB and BFT (p < 0.05). BFT had the higher standard bacterial count, SYNB had the higher Bacillus sp. count, and AUT and CTL showed the lower microbial counts (p < 0.05). The zootechnical performance: final weight, yield, SGR, FCR, feed efficiency and Fulton condition factor were better (p < 0.05) in the BFT and SYNB treatments as compared than to the AUT and CTL. The FI (feed intake) did not show statistical differences between treatments (p > 0.05). Regarding survival, the lower (p < 0.05) was observed in the control treatment. Therefore, we can conclude that the BFT and SYNB systems are promising for improving the results of nitrogen compounds (TAN and N-NO2) control, water footprint, plankton community, bacterial and zootechnical production of juvenile Nile tilapia.

CC chemokine ligand 17 (CCL17) is a CC chemokine present in various species, including fish and mammals. CCL17 plays an important role in various organs, including innate immune defense in mammals, but its role and histological expression in fish have not been elucidated yet. Black rockfish (Sebastes schlegelii) is an economically important aquatic organism in East Asia that has recently been damaged by diverse biological and environmental factors, resulting in enormous financial losses. Although the functions of various immunomodulatory genes in black rockfish have been studied, the histological expression and function of CCL17 from S. schlegelii (SsCCL17) have not been investigated. We conducted homology analysis of the SsCCL17 amino acid sequence in black rockfish by comparing it with those of mammalian, avian, and fish species. Additionally, we proved that SsCCL17 was considerably activated in the ovary and brain of black rockfish using histological analyses via staining with hematoxylin and eosin and in situ hybridization. Moreover, in primary cells collected from the ovarian tissues of black rockfish, cell cycle progression and the expressions of ovarian development-related genes in response to female reproductive hormones were confirmed by quantitative PCR. Finally, the modulatory role of SsCCL17 in ovarian development was assessed using siRNA transfection in primary cells isolated from ovarian tissues of black rockfish, Collectively, we determined the tissue-specific localization of SsCCL17 and its function in the ovary of S. schlegelii, for the first time.

Filamentous fungi have potential as an alternative protein source for use in aquafeeds due to their high protein content and bioactive components. Paecilomyces variotii (PEKILO® mycoprotein) is a β-glucan- and nucleotide-rich filamentous fungi with a crude protein (CP) content of 60–70%. A 9-week feeding trial was conducted to evaluate the effects of P. variotii in diets for Atlantic salmon (initial average body weight of 24 g fish−1) reared in freshwater. Four experimental diets were formulated. Diet 1 was a control diet based on fish meal, soy protein concentrate, and wheat gluten meal. Diets 2, 3, and 4 were formulated so that P. variotii replaced 5, 10, and 20% of the CP content of the diets, respectively. Results showed that dietary inclusion of P. variotii was associated with changes in physical pellet quality, including significant linear (p < 0.0001) and/or quadratic (p < 0.01) decreases in pellet length, width, expansion, and durability. Conversely, significant linear (p < 0.0001) and quadratic (p < 0.025) increases in water activity, bulk density, and water stability index were associated with increasing replacement of the CP content of the diets with P. variotii. There were no significant differences in weight gain, growth rate or feed intake among fish fed the experimental diets (p > 0.05), but a significant linear improvement (p < 0.025) in feed conversion ratio (FCR) with increasing dietary inclusion of P. variotii was observed. The apparent digestibility coefficients for CP and gross energy of the experimental diets decreased linearly (p < 0.01) with increasing dietary levels of P. variotii. Similar results were observed for the essential and non-essential amino acids. Despite reduced digestibility, linear increases in nitrogen (p < 0.01), energy (p < 0.025), and mineral (p < 0.001) retention efficiencies were associated with increasing dietary levels of P. variotii. In the distal intestine, dietary inclusion of P. variotii resulted in significant (p < 0.05) upregulation of several cytokines (ifng, il10, and tgfb), effector molecules (inos, arg1, sod), and transcription factors (irf4), suggesting both activation and control of the inflammatory response in this key mucosa-associated lymphoid tissue. Overall, replacement of 20% of the CP content of the diet with P. variotii reduced digestibility of the experimental diets, but did not affect growth performance and improved FCR and nutrient utilization efficiency of salmon. Thus, P. variotii is a promising ingredient with potential for use in salmonid aquafeeds to improve fish performance and health.