Insect meal in aquafeeds: A sustainable path to enhanced mucosal immunity in fish.

The mucosal surfaces of fish, including their intestines, gills, and skin, are constantly exposed to various environmental threats, such as water quality fluctuations, pollutants, and pathogens. However, various cells and microbiota closely associated with these surfaces work in tandem to create a functional protective barrier against these conditions. Recent research has shown that incorporating specific feed ingredients into fish diets can significantly boost their mucosal and general immune response. Among the various ingredients being investigated, insect meal has emerged as one of the most promising options, owing to its high protein content and immunomodulatory properties. By positively influencing the structure and function of mucosal surfaces, insect meal (IM) has the potential to enhance the overall immune status of fish. This review provides a comprehensive overview of the potential benefits of incorporating IM into aquafeed as a feed ingredient for augmenting the mucosal immune response of fish.

Higher acclimation temperature affects growth of rohu (Labeorohita) through suppression of GH and IGFs genes expression actuating stress response.

Water temperature alone can affect the growth, metabolic rates and physiological responses of aquatic organisms. Our earlier study reported that higher temperature affects cellular and hemato-biochemical responses in rohu, Labeo rohita. In this backdrop, the present study assessed the effect of higher acclimation temperature on the regulatory mechanisms of growth and stress responses of juvenile L. rohita acclimatized in three temperature conditions (30 °C, 33 °C, and 36 °C) for a period of 30 days. The relative expression of genes for growth hormone (GH), insulin-like growth factors (IGF-1 and IGF-2) and heat shock proteins (hsp70 and hsp90) were measured by real-time quantitative PCR. The results revealed that the highest acclimation temperature (36 °C) significantly decreased the weight gain (WG) and specific growth rate (SGR), and increased the feed conversion ratio (FCR) compared to 30 °C (control), while increased WG, SGR and lowered FCR were observed in fish reared at the intermediate temperature (33 °C) compared to 30 °C. Similarly, the GH gene expression in the pituitary was significantly decreased and increased at 36 °C and 33 °C, respectively as compared to 30 °C. A significantly lower expression of IGF-1 and IGF-2, and higher expression of hsp70 and hsp90 were observed in the liver of fish at 36 °C. The results of the present study indicate that although slightly elevated temperature promotes the growth of juvenile L. rohita, the higher acclimation temperature may induce stress response and impair growth performance by suppressing GH/IGF system.

High temperature acclimation alters upper thermal limits and growth performance of Indian major carp, rohu, Labeo rohita (Hamilton, 1822).

Increase in water temperature due to anthropogenic and climatic changes is expected to affect physiological functions of fish. In this study, we determined high temperature tolerance (CTmax) of a common aquacultured Indian major carp, rohu, Labeo rohita fingerlings (15.96 ± 0.72 g BW, 11.56 ± 0.42 cm TL) followed by acclimatization at three temperatures (30, 33, 36 °C). To determine the CTmax, we analyzed the major hemato-biochemical indices - hemoglobin (Hb), red blood cell (RBC), white blood cell (WBC), blood glucose levels, and erythrocytic nuclear abnormalities (ENAs) and erythrocytic cellular abnormalities (ECAs) of peripheral erythrocytes in the fish sampled at the start and end point at each acclimated temperature. Significantly decreased CTmax of the fish was found at 36 °C compared to 30 °C and 33 °C. The fish in the highest (36 °C) temperature were found with significantly lower Hb and RBC content and significantly higher WBC and blood glucose levels than that of the fishes in the lowest (30 °C) temperature both at the start and end points. The highest frequencies of ENAs and ECAs were found in the highest (36 °C) temperature group compared to the lowest (30 °C) temperature group at both the points. We also evaluated growth performance of the rohu fingerlings reared in the three temperatures for 60 days. The growth parameters - final weight gain, percent weight gain and specific growth rate were the highest at 33 °C and the lowest at 36 °C. The present study revealed that the highest temperature (36 °C) tested here may be hazardous to rohu and the temperature should be kept below 36 °C in the aquaculture setting to avoid physiological damage and growth and production loss to the fish.

Extreme warm acclimation temperature alters oxygen consumption, micronucleus formation in erythrocytes, and gill morphology of rohu (Labeo rohita) fingerlings.

Experiencing the seasonal variation and rapid global warming in the tropical climate is a common phenomenon which challenged the aquatic organisms to adapt the physiology and behavior. To investigate the effect of high-temperature acclimation, we selected Indian major carp, rohu (Labeo rohita), a commercially important freshwater aquaculture species. Oxygen consumptions, micronucleus formation in erythrocytes, and gill histopathology were observed in L. rohita fingerlings acclimated at three temperatures (30, 33, and 36 °C) for 30 days. Results showed that the highest acclimated temperature (36 °C) induced higher oxygen consumption and increased frequency of micronucleus formation in erythrocytes. Severity of different histological alterations (hyperplasia, epithelial necrosis, telangiectasis, epithelial lifting, and hypertrophy of chloride cells) in the gills was found to be increased in the highest acclimated temperature (36 °C). These findings indicate the temperature induced adaptive responses and climate vulnerability in a changing environment.

Thermal stress causes nuclear and cellular abnormalities of peripheral erythrocytes in Indian major carp, rohu Labeo rohita.

Rise of water temperature as a consequence of global warming is anticipated to affect the physiological activities of fish, especially in tropical regions. In the present experiment, we exposed the Indian major carp, rohu Labeo rohita to three different temperature regimes (30 °C as control and 33 °C and 36 °C) for 60 days and observed the effects of these temperature on: major hemato-biochemical indices (Hemoglobin; Hb, Red blood cell; RBC, White blood cell; WBC and blood glucose levels), erythrocytic nuclear abnormalities (ENA), and erythrocytic cellular abnormalities (ECA) of peripheral erythrocytes along with the formation of differential leucocytes in the blood. Fish were sacrificed at day 7, 15, 30 and 60 after the start of exposure to the temperature regimes. Hb decreased significantly on days 7 and 15 at 36 °C. Throughout the study period, the decrease of RBC and increase of WBC were significant at 36 °C. Blood glucose level increased significantly initially at day 7 but decreased significantly at day 60 at 36 °C. Frequencies of ENA (binucleated, nuclear bud, nuclear bridge, karyopyknosis and notched nuclei) and ECA (twin, fusion, echinocytic, spindle, tear drop and elongated shaped) were significantly increased at the highest temperature (36 °C) at almost all of the sampling days. In the case of differential leucocyte count, high temperature caused a significant increase in the number of neutrophils and a significant decrease in the number of lymphocytes. Overall, these results indicate that chronic exposure to high temperature (36 °C) induces a number of stress responses in rohu and that temperature should be kept below 36 °C in the aquaculture setting to avoid damage to the fish.

Vitamin E supplementation in diet ameliorates growth of Nile tilapia by upgrading muscle health.

Vitamin E (VE), an important lipid-soluble antioxidant, has great influence on growth and maintenance in animal. The effects of VE supplemented diet on growth and feed usage in Nile tilapia (Oreochromis niloticus) was investigated in this study. Three formulated diets containing VE (0, 50 and 100 mg/kg) were fed to Nile tilapia (3.56 ± 0.16 g) in glass aquaria maintaining three replicate groups for 56 days (8 weeks). Survival, growth performance including weight gain, percent weight gain, and specific growth rate (WG, % WG, and SGR), and feed utilization comprising protein efficiency ratio and feed conversion ratio (PER and FCR) were calculated. Hemato-biochemical indices including hemoglobin level (Hb), white blood cell (WBC), red blood cell (RBC) and glucose level were analyzed. In addition, muscle morphology was examined after completion of the experiment. At the end of the trial, WG, %WG, SGR, FCR and PER increased significantly which had dietary VE supplimentation. However, no distinct changes were observed in Hb level, RBC count, WBC count and glucose level among these different dietary groups. Dietary VE treatments significantly upgraded the muscle fiber diameter and lowered the intra-muscle gap. Moreover, quantity of hyperplastic muscle fiber as well as nucleus also significantly enhanced by VE. Morphological structure of muscle characterized by a huge proportion of hyperplastic muscle that may be supposed to contribute the enhanced growth of Nile tilapia receiving VE supplemented diet. Therefore these results suggested that VE incorporation into the feed can be effective to improve the feed efficiency and maximize the growth of O. niloticus.

Presence of microplastics in two common dried marine fish species from Bangladesh.

We examined microplastics (MP) in two commercially important dried fish, Bombay duck (Harpadon nehereus) and ribbon fish (Trichiurus lepturus), collected from two sites on the Bay of Bengal (Cox's Bazar and Kuakata). The number of MP found in dried Bombay duck and ribbon fish from Kuakata was significantly higher (41.33 g-1 and 46.00 g-1, respectively) than the MP present in samples collected from Cox's Bazar (28.54 g-1 and 34.17 g-1, respectively). Fibers were the most common type of MP identified in all samples (41-64%), followed by fragments (22-34%), microbeads (9-16%), films (3-4%), foams (1-4%), and pellets (0-2%). ATR-FTIR analysis revealed three different types of MP polymer - polyethylene (35-45%), polystyrene (20-30%) and polyamide (30-45%) in the dried fish samples. The study confirms the presence of high MP loads in dried fish from the Bay of Bengal, with high potential of trophic transfer of MP to the human body.

Alterations in hematological parameters and the structure of peripheral erythrocytes in Nile tilapia (Oreochromis niloticus) exposed to profenofos.

The burden of pesticide use from agricultural intensification lies in the fact that pesticides may end up in aquatic ecosystems and have pernicious effects on non-target organisms, including fish. Different blood biomarkers, including hemato-biochemical indices, erythrocytic nuclear abnormalities (ENA), and erythrocytic cellular abnormalities (ECA), were observed in Nile tilapia (Oreochromis niloticus) after exposure to varying sub-lethal concentrations (0%, 5%, 10%, 20%, and 40% of 96-h LC50) of profenofos at different time intervals (7, 14, 21, and 28 days). The results revealed that glucose and white blood cell (WBC) levels significantly increased, while hemoglobin, red blood cell (RBC), and packed cell volume (PCV) significantly decreased in a time- and concentration-dependent manner. Aberrant erythrocytic morphology-derived ENA, such as nuclear degeneration, micronuclear formation, binuclear development, nuclear budding, and karyopyknosis, significantly increased with time in profenofos-exposed groups compared to controls. Between the treatment and control groups, a significant execution was discerned for teardrop and fusion type ECA. For other cellular aberrations of erythrocytes, including elongated, twin, and spindle, a significant difference appeared only at the beginning of the experiment (day 7). This study concludes that the presence of widely used profenofos in aquatic systems has a pernicious effect on Nile tilapia.

Chromium Exposure Causes Structural Aberrations of Erythrocytes, Gills, Liver, Kidney, and Genetic Damage in Striped Catfish Pangasianodon hypophthalmus.

Heavy metal pollution due to anthropogenic activities poses a great threat to aquatic organisms. The present study was conducted to evaluate the cytotoxic and genotoxic effects of hexavalent chromium (potassium dichromate) on hemato-biochemical, histo-pathological, and genetical changes in striped catfish Pangasianodon hypophthalmus. Three sub-lethal doses (0.8, 1.6, and 3.2 mg/L) of chromium (Cr) were selected and fish were exposed in vivo contrasting with a control (0 mg/L) for 30 days. The study revealed that various hemato-biochemical parameters showed a significant decrease in hemoglobin (Hb), red blood cells (RBCs), and blood glucose content, whereas white blood cells (WBCs) significantly increased in Cr exposed fish. Frequencies of all forms of structural abnormalities of erythrocytes (erythrocytic cellular abnormalities; ECA, erythrocytic nuclear abnormalities; ENA and erythroblasts; Ebs) were significantly increased in higher two test concentrations (1.6 and 3.2 mg/L) when compared to control. Differential leucocyte count exhibited significant increase in neutrophil and decrease in lymphocytes in the highest Cr treated group. The severity of various histo-pathological changes in the gills, liver, and kidney were increased considerably with the increase of Cr concentrations. Similarly, the amount of DNA (ng/µl) decreased significantly in blood and tissues of different vital organs where the liver showed the highest decline compared to control in a concentration-dependent manner. Taken altogether, P. hypophthalmus is susceptible to Cr and can be used as a bio-indicator to assess aquatic metal pollution.

Toxicity of the organophosphate insecticide sumithion to embryo and larvae of zebrafish.

Sumithion, a synthetic organophosphate, is widely used as an agricultural insecticide and for control of tiger bug (Cicindela spp.) in larval rearing for aquaculture. An experiment was conducted to examine the effects of sumithion on embryological and larval development of zebrafish Danio rerio. Fertilized egg (n = 100) and larvae (n = 100) were exposed to six concentrations of sumithion (0, 0.1, 0.2, 0.4, 0.8 and 1.6 mg L-1) in three replicates. LC50 values for embryos and larvae were calculated by probit analysis. The 24 h LC50 value of sumithion for embryo was 0.235 (0.079-0.428) mgL-1. Increasing sumithion concentrations decreased hatching success and increased embryonic mortality. In embryos, sumithion induced several malformations including immature yolk sac, dark yolk sac, yolk sac bud, broken eggshell and notochord, unhatched eggs. Larval LC50 values at 24, 48 and 72 h of various doses of sumithion exposure were 0.620 (0.436-0.963), 0.475 (0.302-0.801) and 0.341 (0.177-0.617) mgL-1, respectively. Various physical deformities, including edema, notochord deformity, yolk sac damage, body arcuation, lordosis and black pigmentation on the yolk sac were evident in response to different concentrations of sumithion. The results of the current study indicate that sumithion exerts developmental toxicity to zebrafish embryos and larvae. It is expected that current findings will increase sensitivity about the toxic effect of sumithion in early development, as well the possibility of similar actions induced by other insecticides and pesticides.

Nuclear and Cellular Abnormalities of Erythrocytes in Response to Thermal Stress in Common Carp Cyprinus carpio.

As a consequence of global warming, increase of water temperature is likely to alter physiological functions of fish. Hence, we examined the effects of high temperature on blood glucose, hematological parameters [hemoglobin (Hb), red blood cell (RBC), and white blood cell (WBC)], and nuclear and cellular structure of blood cells of common carp (Cyprinus carpio) after exposure to three temperature regimes (27, 31, and 35°C) for 14 days. Fish were sacrificed on 3, 7, and 14 days of exposure. The blood glucose level increased significantly in the fish exposed to 35°C compared to 27 and 31°C. The Hb and RBC contents decreased but WBC increased significantly in the blood of fish exposed to 35°C compared to 27 and 31°C at 7 and 14 days of exposure. Consequently, the frequencies of erythroblasts (Ebs), erythrocytic nuclear abnormalities (ENA), and erythrocytic cellular abnormalities (ECA) were found to be increased in the blood of fish exposed to 35°C compared to 27 and 31°C. There was a significant increase in neutrophils and decrease in lymphocytes in the highest temperature (35°C). With increasing temperature, dissolved oxygen (DO) decreased but free CO2 increased significantly during the study period. The present study demonstrated that common carp are better adapted to 27 and 31°C environmental temperatures, while the higher temperature 35°C is likely stressful to this fish species.

Acute effects of chromium on hemato-biochemical parameters and morphology of erythrocytes in striped catfish Pangasianodon hypophthalmus.

Chromium is considered the most detrimental pollutant to the aquatic organisms. The present experiment was conducted to determine the acute toxicity of chromium in view of its effects on hemato-biochemical parameters and the structure of erythrocytes in striped catfish, Pangasianodon hypophthalmus. Fish were exposed to seven different concentrations (0, 10, 20, 30, 40, 50 and 60 mg/L) of chromium, each with three replications for 96 h. After 96 h of exposure, the survived fish were sacrificed to measure hemato-biochemical parameters (hemoglobin, Hb; red blood cell, RBC; white blood cell, WBC; packed cell volume, PCV; mean corpuscular volume, MCV; the mean corpuscular hemoglobin, MCH and blood glucose). In addition, erythrocytic cellular abnormalities (ECA) and erythrocytic nuclear abnormalities (ENA) of peripheral erythrocytes were assayed. No mortality was observed up to 10 mg/L, but 90% and 100% mortality was observed at 50 mg/L and 60 mg/L, respectively after a 96 h exposure period. The 96 h LC50 value through probit analysis was 32.47 mg/L. Hb (%), RBC (×106/mm3) and PCV (%) significantly decreased at 20, 30 and 40 mg/L of chromium, whereas WBC (×103/mm3), MCV (µm3) and MCH (pg) showed the opposite scenario. Blood glucose (mg/dL) levels significantly increased at 10, 20, 30 and 40 mg/L of chromium compared to 0 mg/L. Frequencies of ECA and ENA significantly increased with increasing chromium concentrations. This study indicates that chromium is highly toxic to striped catfish.

Acute toxicity of an organophosphate insecticide sumithion to striped catfish Pangasianodon hypophthalmus.

Sumithion is widely used for crop safety and eradication of tiger bugs (Cicindela spp.) from larval rearing aquaculture ponds. To satisfy the high demand of fries and fingerlings of widely cultured species striped catfish, spawns are produced in large scale in the hatcheries through hormone induced breeding, and subsequently these spawns are reared in nursery ponds and marketed to fingerlings vendors for stocking in grow-out ponds. Considering the importance of healthy fries and fingerlings the present experiment was conducted to evaluate the toxic effects of sumithion on striped catfish fingerlings. Fish were exposed for 96 h to six concentrations of sumithion (0, 3, 4, 5, 6 and 7 mg/l) each with three replications. The 96 h LC50 value was calculated using probit analysis. After 96 h of exposure fishes were sacrificed to measure hemato-biochemical (Hemoglobin, Hb; Red blood cell, RBC; White blood cell, WBC and blood glucose) parameters. In addition, formation of micronucleus (MN) was examined in the blood erythrocytes. The 96 h LC50 value of sumithion for striped catfish was 5.886 mg/l. The values of RBCs and Hb decreased significantly in different concentrations of the toxicant compared to control, while the values of WBC and blood glucose levels showed opposite scenario. Consequently, the frequencies of formation of MN increased significantly in different concentrations of the toxicant compared to the control. The results of the current study denoted that sumithion exerts toxicity to striped catfish. It is expected that the findings of the present research will help in the development of awareness of the concerned people about the toxic effect of sumithion as well as other insecticides and pesticides in the environment.

Increase in water temperature increases acute toxicity of sumithion causing nuclear and cellular abnormalities in peripheral erythrocytes of zebrafish Danio rerio.

Global warming and indiscriminate usages of pesticides are notable concern to all. The present study has been conducted to evaluate the effects of high temperature on acute toxicity of sumithion in adult zebrafish. A 2-day renewal bioassay system was used to determine the 96 h LC50 value of sumithion at three temperature regimes, such as 25 °C, 30 °C, and 35 °C. Blood glucose (mg/dL) level was measured in control (0.0 mg/L) and low concentration (1.0 mg/L) of sumithion during the determination of LC50 in three temperature conditions. In addition, micronucleus (MN), erythrocytic nuclear abnormalities (ENA), and erythrocytic cellular abnormalities (ECA) tests were performed in the blood erythrocytes. The 96 h LC50 value of sumithion for zebrafish was significantly lower at 35 °C, which indicates that the toxicity of sumithion increases at higher temperature. Blood glucose level was significantly increased by sumithion in all temperature conditions, while it was significantly higher in the highest (35 °C) temperature compared to the lowest (25 °C) temperature in both control and sumithion-treated fish. Similarly, frequencies of MN, ENA, and ECA were elevated by sumithion in all temperature conditions, whereas it was significantly raised in the highest (35 °C) temperature compared to the lowest (25 °C) temperature in both control and sumithion treated fish. With increasing temperature in exposure to sumithion, dissolved oxygen decreased significantly, whereas free CO2 increased significantly. On the other hand, no distinct changes were observed in pH and total alkalinity during the experimental period. Therefore, it can be inferred that increasing temperature enhances the toxicity of sumithion in the zebrafish.