Dietary Fish Research Articles

Temporal and Spatial Dynamics of Plankton Communities in the Lower Haora River, Tripura, India

Planktons are significant bioindicator of ecosystem functioning, knowledge of the seasonal fluctuation in the plankton population in riverine waters of Indian subcontinent is rather limited. In the present study, analysis regarding spatio-temporal variations based on different multivariate statistics and indicator value analysis is done along with analysis of community structure of plankton assemblages. A total of 46 plankton taxa out of which 38 phytoplankton and 8 zooplankton taxa have been identified based on examination of samples taken from four locations over three sampling seasons. The primary phytoplankton families that involve Chlorophyceae, Bacillariophyceae, Cyanophyceae, Euglenophyceae and Composopogonophyceae. Chlorophyceae dominated the phytoplankton population, followed by Bacillariophyceae and Cyanophyceae. The plankton abundance was recorded highest in spring, followed by winter, and the least reported in monsoon season. The high average percent contribution of Aulacoseira, Oscillatoria, and Spirogyra species is well represented through SIMPER analysis. In addition, the Shannon–Wiener index (H) was calculated to determine plankton diversity, and Pielous' Evenness index (E) was calculated to determine individual distribution within a community whereas Margalef’s Richness index showed species richness of the study area. This qualitative and quantitative study will aid future research on the occurrence of plankton as well as the more trustworthy information generation on fish diet and feeding behaviors. The condition of planktons as bioindicators would indirectly provide an estimation of the ecosystem's natural state or amount of pollution.

Angling bait consumption and stable isotope niche of two cyprinids in different lake fisheries

Abstract Terrestrial subsidies are important for freshwater ecosystems and, in lakes supporting recreational fisheries, angling baits can represent an important allochthonous input. This resource can directly contribute to fish diet but its consumption may be influenced by fish body size and the type of angling baits used in different fisheries. In this study, we evaluated angling baits consumption by two common cyprinid species, Cyprinus carpio and Rutilus rutilus, in three fishery types (specialised carp, specialised roach, and put‐and‐take fisheries). We used stable isotope analyses (δ13C and δ15N) of cyprinids, their natural prey and different angling baits in 16 gravel pit lakes located in south‐western France, including four lakes without angling. Angling baits were significantly δ13C‐enriched and δ15N‐depleted compared to natural prey. Overall, angling bait consumption was highly variable between individuals. For C. carpio, angling bait consumption averaged 30.5% (±17.0 SD) and was higher in specialised carp fisheries (40.0% ± 16.7 SD) than in put‐and‐take fisheries (15.9% ± 9.0 SD) and was not related to body size. For R. rutilus, angling bait consumption averaged 41.3% (±15.7 SD), did not differ significantly among fishery types, but increased with body size. The niche width of C. carpio was six times larger in specialised carp fisheries than in lakes without angling. For R. rutilus, niche width was two times larger in specialised carp and put‐and‐take fisheries compared to lakes without angling and specialised roach fisheries. These results indicate that angling bait subsidies represent a novel and substantial resource opportunity for fishes in angling lakes, with trophic consequences for the targeted species through increase of their stable isotope niche size. These impacts are partly influenced by the type of angling baits used by anglers and the characteristics of the fisheries, suggesting the need for improved quantification of the temporal dynamics of this type of subsidy to better understand its consequences on freshwater fish and recipient ecosystems.

Unravelling a specialised diet of an Amazonian catfish in a controlled flood-pulse area by combining stomach-content and stable-isotope analyses

Context Hydrological dynamics are crucial in fish ecology. Aims To evaluate the effect of the flood pulse on the feeding ecology of Doras higuchii in the reduced-flow section of the Belo Monte dam, Xingu River, Brazil. Methods Collections were conducted between December 2020 and November 2021. The fish were measured and had their stomachs removed. Muscle tissue was also extracted for stable-isotope analysis. Stomach contents were inspected to assess diet, testing the influence of hydrological periods by using GLM. In addition, we evaluated the effect of the flood pulse on the δ13C and isotopic ratios of individuals Results In total, 362 specimens of D. higuchii were analysed, highlighting a diet mainly on the basis of sediment (74.9%) and aquatic insects (24.8%), not varying between periods characterising the species as a specialist for having detritivorous habit, as well as the extension of the trophic niche. There was variation in food intensity, with higher average food consumption in the flood period. The isotopic composition (δ13C and δ15N) also did not differ between periods. Finally, δ15N did not vary by length class. Conclusions This information helps understand the interface between environmental and biological factors in an environment affected by a hydroelectric dam. Implications Our results may help fill gaps in knowledge about the diet of doradid fishes.

Diet and habitat as determinants of intestine length in fishes

AbstractFish biologists have long assumed a link between intestinal length and diet, and relative gut length or Zihler’s index are often used to classify species into trophic groups. This has been done for specific fish taxa or specific ecosystems, but not for a global fish dataset. Here, we assess these relationships across a dataset of 468 fish species (254 marine, 191 freshwater, and 23 that occupy both habitats) in relation to body mass and fish length. Herbivores had significantly relatively stouter bodies and longer intestines than omni- and faunivores. Among faunivores, corallivores had longer intestines than invertivores, with piscivores having the shortest. There were no detectable differences between herbivore groups, possibly due to insufficient understanding of herbivorous fish diets. We propose that reasons for long intestines in fish include (i) difficult-to-digest items that require a symbiotic microbiome, and (ii) the dilution of easily digestible compounds with indigestible material (e.g., sand, wood, exoskeleton). Intestinal indices differed significantly between dietary groups, but there was substantial group overlap. Counter-intuitively, in the largest dataset, marine species had significantly shorter intestines than freshwater fish. These results put fish together with mammals as vertebrate taxa with clear convergence in intestine length in association with trophic level, in contrast to reptiles and birds, even if the peculiar feeding ecology of herbivorous fish is probably more varied than that of mammalian herbivores.

A realistic combined exposure scenario: effect of microplastics and atrazine on Piaractus mesopotamicus.

Microplastics, considered emerging environmental contaminants resulting from plastic degradation, are discovered in diverse aquatic ecosystems and can be unintentionally ingested by fish. Therefore, it is essential to characterize their interaction with other contaminants, such as agrochemicals, in aquatic environments. This study aimed to assess histological, enzymatic, and genotoxic biomarkers in juvenile pacú (Piaractus mesopotamicus) exposed to polyethylene (PE) microplastic particles and the herbicide atrazine, individually or combined, for 15 days. Four treatments were used: a negative control (CON), PE in the fish diet (0.1% w/w, FPE), atrazine through water (100 μg L-1, ATZ), and the mixture (ATZ+FPE). Results confirmed histological alterations in gills (edema and lamellar fusion) and liver (necrotic areas and congestion) of fish exposed to ATZ and ATZ+FPE. The number of goblet cells increased in the posterior intestine of fish under ATZ+FPE compared to CON and FPE. Enzyme activities (CAT, GST, AChE, and BChE) significantly increased in ATZ+FPE compared to CON. However, no genotoxic effect was demonstrated. These findings provide insights into the complex impacts of simultaneous exposure to atrazine and microplastics, emphasizing the need for continued research to guide effective environmental management strategies against these contaminants that represent a risk to aquatic organisms.

To Standardise Parameters for Preparation of Extruded Feed Using Various Conventional and Non-Conventional Ingredients

The purpose of this research was to optimise extruder parameters for the preparation of floating fish diets with appropriate physicochemical qualities. The impact of temperature (90-120oC), moisture content (15%-30%), die diameter (2.0-4.0 mm) and pre-conditioning duration (15-30 m) on physical properties of the pellets such as bulk density, floatability, expansion ratio and water stability, were examined. Accordingly, four iso-nitrogenous (crude protein 35%) experimental diets were formulated for GIFT tilapia advance fry by replacing 50% of GNOC protein of the control diet (T0) by sunflower oilcake (SFOC) (T1), by linseed oilcake (LSOC) (T2) and by fish based silage (T3) protein. The pellets extruded using a combination of 120 oC extruder barrel temperature, 25% moisture content of feed mix, 2.0 mm die diameter and 30 minute of pre-conditioning duration gave most required pellet floatability (90-100%), expansion ratio (1.43-1.61), water stability (95-99%) and bulk density (0.8 - 0.9 g/cm3) for T1 and T2. However, fish silage when incorporated in the feed mix, it affected negatively in all the physical characteristics of a floating feed and resulted in higher bulk density and lower floatability, expansion ratio and also water stability.

Lake food web structure in Teici Nature reserve, Latvia: fish presence shapes functioning of pristine bog lake food webs

AbstractStudies on the effects of fish presence on lake ecosystems are widespread but only a few have been conducted in pristine aquatic environments. We employed Ecopath model for assessing food web structure in two fish-inhabited and one fishless lake in a pristine bog area. We hypothesized that: (a) fish absence will raise trophic positions of macroinvertebrate predators; (b) fish predation will lead to higher overall predation rates on zooplankton; (c) fish predation on large bodied zooplankton will result in top-down cascading effect, increasing phytoplankton biomasses. We found that fish have direct and indirect effects on zoobenthic communities. Chironomid biomass was greater and predatory macroinvertebrate groups had a higher trophic level in the fishless lake than in fish-inhabited lakes. Consumption rates of the benthic consumer fraction were greater than that of the planktonic fraction in the fishless lake; the opposite was found in the two lakes with fish. No effects of fish presence on zooplankton were found and we explain this partly by the low water transparency masking the impact of fish. Terrestrial insects constituted a crucial part of adult fish diet and we conclude that terrestrial secondary production contributes to the trophic support of fish communities in pristine bog lakes.

Selenium-mercury interactions and relationship to aquatic toxicity: A review.

A review of the literature pertaining to selenium-mercury (Se/Hg) interactions in aquatic species was performed to provide insight into the mechanisms allowing for the reported changes in bioaccumulation and toxicity that have been observed when the two elements occur at elevated concentrations. Selenium (Se) has been shown to protect against mercury (Hg) toxicity in all animal models evaluated (fish, birds, mammals, and plants). To explore the interaction between the two elements, data are presented on concentrations of both elements in wild-caught fish at numerous locations. The data show that most fish have Se/Hg ratios >1.0. The importance of this ratio has been reported, with suggestions that the protective interaction is due in large part to the formation of HgSe. Data show that when the Se/Hg molar ratio is <1.0 in the diet of fish and animals, Hg toxicity will be expressed, provided that the Hg concentration is sufficiently high. This toxicity is likely the result of Se deficiency leading to an excess of reactive oxygen species. Laboratory fish toxicity studies reviewed show that Se toxicity can be reduced or eliminated when Hg is added to the diet in moderate amounts. Field studies have shown reduced accumulation of Hg when Se concentrations are increased. When Hg in the diet is significantly elevated (usually >10 µg/g), toxicity is expressed regardless of the Se present. Likewise, amelioration of Se toxicity by Hg occurs over a limited range. Tissue thresholds for Se toxicity have been derived primarily from studies where fish eggs were extracted from wild fish and embryo deformities were observed; however, the amount of Hg in the fish or ovaries was not considered, which could lead to uncertainty in the toxicity threshold. It is recommended that both elements be measured and evaluated when performing risk assessments and setting water quality criteria. Integr Environ Assess Manag 2024;00:1-11. © 2024 SETAC.

Growth performance, health status, gut microbiome, and expression of immune and growth-related genes of rainbow trout (Oncorhynchus mykiss) fed diets with pea protein replacement of fish meal

The need for fish meal constrains fish farming and significantly impacts sustainability of the aquaculture industry. Hence, it is important to investigate the use of plant-based protein sources in fish diets. The present study was conducted to determine the effects of different levels of fish meal (FM) replacement by pea protein (PP) in a 60-day feeding experiment in rainbow trout, Oncorhynchus mykiss. Effects on growth performance, body composition, hematology, serum biochemistry and immunology, and immune (TNF-α, IL1-ß and Il-8) and growth-related (GH and IGFI) gene expression were investigated. Five experimental diets (45% protein and 20% lipid) differed in replacement level of FM by PP at rates of 0% (control (PP0)), 25% (PP25), 50%(PP50), 75%(PP75) and 100%(PP100). Fish were fed with experimental diets in triplicate twice daily. The best growth performance was obtained in PP0 and PP25 groups. While fat ratios of fish fillets significantly differed (p < 0.05), there was no significant effects on protein ratios (p < 0.05). There was no significant change in the hematological values of fish, except those fed the PP100 diets, which displayed a reduction in eyrthocyte counts, hemoglobin content and hematocrit. As PP supplementation increased fish showed elevated serum glucose, total protein, cholesterol and myeloperoxidase activity and decreased glutamic pyruvic transaminase and alkaline phosphatase activity. Fish fed diets with between 25 and 75% replacement showed a decline in lactic acid bacteria in the gut. Significant increases in expression were observed in the liver of the PP25 fish relative to the 0% control for all immune and growth-related genes except for IL1-ß. These data suggest that up to 25% of FM can be replaced by PP without any adverse effects on rainbow trout.

Temporal changes in the diet composition and trophic level of walleye pollock (Gadus chalcogrammus) inhabiting the middle-eastern coast of Korea

The influences of oceanographic changes on diet composition and trophic level for pollock (Gadus chalcogrammus) inhabiting the East Sea off the Korean coast were examined based on stomach content and stable isotope analyses during 2016 and 2017. The diets of pollock consisted mainly of benthic crustaceans (particularly carid shrimps and euphausiids) and cephalopods, with a predominance of teleosts in the diets of larger individuals in deeper habitats. In 2016, amphipods, carid shrimps and cephalopods featured strongly in pollock diets, and the contribution of amphipods decreased in the diets of larger individuals and deeper depths. In 2017, euphausiids dominated at shallower depths, whereas the contributions of carid shrimps and teleosts increased in deeper habitats. Body-size-related differences in carbon stable isotope (δ13C) values were present in both 2016 and 2017, but size-related differences in nitrogen stable isotope (δ15N) values were only observed in 2017. The increased contribution of euphausiids during 2017 resulted in a distinct decrease in the trophic level of pollock compared to co-occurring higher trophic level predators, which can be linked to changes in habitat water temperature. Combined stomach contents and isotopic analyses provide a more comprehensive understanding of how fish diets and trophic levels fluctuate with changes in the type and abundance of prey resources in response to environmental changes.

Asymmetrical individual both left and right otoliths of Tuna Scombrini collected from the Java Sea

Otolith can be used as a natural marker of fish stock or anomalies between individuals within fish stock. This research aims to study the relationships between fish length and otolith length and confirm differences in otolith shape between species in the Scombrini tribe and Carangidae family (Decapterus ruselli). Sample used in our analysis were collected around July - September 2023 from three different location, Rastrelliger brachysoma (Lekok waters, Pasuruan), Scomber australasicus (Bali Strait waters) and Decapterus ruselli (Sendang Biru, South Malang). Total 96 specimens were identified based on morphological character as Rastrelliger brachysoma, Scomber australasicus and Decapterus ruselli. Each of following samples were cut horizontally at the frontal head to open the skull and remove sagitta otolith below the hindbrain using dissecting set, then cleaned and stored dry in microtube 1,5 ml separately for left and right to further documented using Celestron Digital Microscope Pro Gray USB 44308. Otolith morphometric data collected includes maximum length using TpsDig and weight using analytical balance. The relationship between Forked Length (FL) and otolith length, length-weight relationship of otolith was determined using simple linear regression on software Statistical Product and Service Solutions (SPSS). Paired sample t-test was applied to determine asymmetrical size of left and right otoliths. In this study, it was found that the shape of the otoliths between species has differences in the rostrum, antirostrum, ventral and dorsal parts. FL-otolith length relationship of S. australasicus, R. brachysoma and D. ruselli are Y=0,725+0,164X, r2= 0,519; Y=0,191+0,230X, r2= 0,911; Y=3,156+0,075X, r2=0,071 respectively. The LW sagitta relationship shows that there is a very strong relationship (P<0,05) between L and W of otoliths. The results of the Paired Sample T-test showed that there was no significant difference in the size of the left and right otoliths (Sig>0.05). Otolith shape is influenced by fish behaviour, diet and environment and it may be used as additional information to distinguish between tribe or even species. Otherwise, its asymmetric relationship and LW relationship may be potential new methods for stock discrimination and have other implications such as stock assessment, understanding natural asymmetry, and its potential applications in fisheries management and conservation.

Type of black soldier fly (Hermetia illucens) larvae frass influences the nutritional value when included in a prepared diet for Mozambique tilapia (Oreochromis mossambicus)

Black soldier fly (Hermetia illucens) larvae (BSFL) farming is expected to increase, and a by-product is the ‘frass’. The dietary inclusion of BSFL frass has been shown to enhance tilapia and catfish growth/immunity. However, the composition of BSFL frass, and potentially their nutritive value to fish, may depend on the initial provided substrate. In this 8-week nutrition trial, BSFL frass made from either expired fish diet (EFD; 45% crude protein) or a combination of fruits/vegetable peels (FV; 9.3% crude protein) were included in the diets of Mozambique tilapia (Oreochromis mozambicus) at 5% or 10%. The EFD and FV frass had a different nitrogen, mineral, and amino acid profile, and this information was used to formulate the diets. Results showed that EFD frass at 10% significantly (P < 0.05) enhanced tilapia growth compared to fish fed the control diet, but performance of fish fed the other test diets were not different (P > 0.05) from the control. There was no significant difference in the crude protein or lipid content of tilapia, but some differences were observed in the amino acid and fatty acid composition. Among the test minerals, only phosphorus was significantly affected, which was higher in tilapia fed the FV frass diets. Liver histology showed some minor inflammation and blood vessel congestion in tilapia fed the 10% frass diets, while the intestinal histology had a better cumulative score among all the frass diets compared to the control. Results indicate that the initial substrate provided to the BSFL can influence the nutritive value of the frass to fish.

Effects of Dietary Fish Meal Replaced by Cottonseed Protein Concentrate on Growth Performance, Antioxidant Capacity, and Liver and Intestinal Health of Juvenile Hybrid Culter

The objective of this study was to assess the impact of concentrated cottonseed protein (CPC) as a substitute for fishmeal (FM) in juvenile hybrid culter (Erythroculter ilishaeformis ♀ × Ancherythroculter nigrocauda ♂). A total of 360 fish with an initial body weight of 10.0 ± 0.5 g were randomly allocated into 12 indoor culture tanks, with each tank containing 30 fish. Four diets were formulated in which fish meal (FM) was replaced by CPC at different inclusion levels: 0% (T0), 15% (T15), 30% (T30), and 45% (T45). The corresponding amounts of CPC included were 0, 61, 122, and 182 g/kg, respectively. At the end of the 10-week feeding trial, the findings revealed an inverse correlation between the proportion of CPC replacing FM and both final body weight (FBW) and weight growth rate (WGR) in hybrid culter. Specifically, the T30 and T45 groups exhibited significantly lower FBW and WGR compared to the T0 group (p &lt; 0.05). No significant differences in crude protein and ash contents were observed among all groups (p &gt; 0.05). However, the crude lipid content was highest in hybrid culter fed the T45 diet and lowest in the T0 group (p &lt; 0.05). There were no significant differences in muscle amino acid composition among all treatment groups (p &gt; 0.05). The contents of total protein (TP) and albumin (ALB) declined slightly as the proportion of FM substituted by CPC increased, yet this decline did not reach statistical significance (p &gt; 0.05). Serum alanine aminotransferase (ALT) activity elevated with increasing dietary CPC, and the T45 group exhibited significantly higher ALT activity compared to the T0 group (p &lt; 0.05). The hepatic activities of superoxide dismutase (SOD) and catalase (CAT) were significantly lower in the T45 group than in the T0 and T15 groups (p &lt; 0.05). Furthermore, there was a decrease in intestinal villi length with an increasing replacement ratio of FM by CPC, and the villi length in the T45 group exhibited a significant reduction when compared to that in the T0 group (p &lt; 0.05). It is concluded that replacing 15% FM with CPC does not exert obviously detrimental effects on growth performance, serum biochemical indices, intestinal morphology, muscle amino acid profile, or antioxidant performance of juvenile hybrid culter.

Effects of Azadirachta indica Leaf Aqueous Extract supplemented Fish Diets on Innate Immune Response and Disease Resistance of Tilapia (Oreochromis niloticus)

Pseudomonas fluorescens is an important bacterial pathogen causing economic losses in aquaculture worldwide. The adverse effects of antibiotics raise public concerns on using them in aquaculture. The objective of this study was to examine the effectiveness of aqueous extract of Azadirachta indica leaves on nonspecific immunity and disease resistance in tilapia (Oreochromis niloticus). Fish diets supplemented with aqueous extract of A. indica at the concentrations of 0% (Diet 1), 1% (Diet 2), 1.5% (Diet 3) and 2% (Diet 4) were investigated for their effects on nonspecific immune response and disease resistance in tilapia. The fish given diet 3 and diet 4 for 3 weeks had increased levels of leukocyte phagocytic activity though higher activity was observed in diet 4 group. Diet 3 and diet 4 also enhanced plasma lysozyme activity in tilapia. The similar levels of lysozyme activity were found in the fish receiving both diets for 3 weeks. Only diet 4 had stimulatory effect on respiratory burst activity in tilapia. This effect was observed 3 weeks after feeding the fish with diet 4. Throughout the experiment, no significant differences (P &gt; 0.05) in phagocytic, lysozyme and respiratory burst activities were found between group fed with diet 1 (control) and diet 2. Following 3 weeks after feeding, fish were infected with Pseudomonas fluorescens at median lethal dose (LD50). No mortality was found in the diet 4 group while 50%, 48% and 28% of cumulative mortality were found in the fish receiving diet 1, 2 and 3 respectively. These results indicate that the aqueous extract of A. indica may elevate the nonspecific immune response and enhance disease resistance in tilapia.

Incorporation of Nano Selenium in Fish Diet and Assessment of Growth Performance and Biochemical Criteria of Labeo rohita

Selenium (Se) is an essential microelement utilized in aqua-feeds for aquatic animals’ normal growth, well-being and health. This work was intended to assess the growth performance of Labeo rohita (Rohu) resulting from the nano Se-merged diet. Nano Se was synthesized and its physico-chemical characteristics were characterized using UV-VIS, SEM, EDAX, XRD and FTIR for varying quantities of nano Se; Diets - I-0, II- 0.5, III-1, IV-1.5, V-2 and VI- 2.5 mg/ kg were prepared, making use of fish meal (FM), groundnut oil cake (GNOC), wheat flour (WF) and tapioca flour (TF). Feed-utilizing parameters and the biochemical composition of Rohu were evaluated subsequently after 28 days. The UV-Vis Spectroscopy revealed that nano Se was assessed in wavelengths of 200 to 500 nm and exhibited strong absorption at 322 nm. SEM image showed spherical morphology with an average particle diameter of 12.22 mm. EDAX spectrum recorded two signals at 1.5 keV and 11 keV. XRD patterns showed crystalline characteristics of nano Se at 2θ correlators of 23.5o, 29.7o, 41.4o, 43.6o, 45.4o, 51.7o, 55.9o and 61.5o. FTIR spectrum was examined in the range of 4000 – 500 cm-1. Rohu's growth performance and biochemical analysis revealed that the protein, carbohydrate and lipids of gill, liver and muscle of Rohu were highly increased in the case of diet IV containing 1.5 mg/kg nano Se.

Dietary tryptophan intervention counteracts stress-induced transcriptional changes in a teleost fish HPI axis during inflammation

Immune nutrition is currently used to enhance fish health by incorporating functional ingredients into aquafeeds. This study aimed to investigate the connections between tryptophan nutrition and the network that regulates the communication pathways between neuroendocrine and immune systems in European seabass (Dicentrarchus labrax). When tryptophan was supplemented in the diet of unstressed fish, it induced changes in the hypothalamic-pituitary-interrenal axis response to stress. Tryptophan-mediated effects were observed in the expression of anti-inflammatory cytokines and glucocorticoid receptors. Tryptophan supplementation decreased pro-opiomelanocortin b-like levels, that are related with adrenocorticotropic hormone and cortisol secretion. When stressed fish fed a tryptophan-supplemented diet were subjected to an inflammatory stimulus, plasma cortisol levels decreased and the expression of genes involved in the neuroendocrine response was altered. Modulatory effects of tryptophan dietary intervention on molecular patterns seem to be mediated by altered patterns in serotonergic activity.

Spatial factors overcome seasonality regulating the consumption of allochthonous food resources by fishes from tropical lotic ecosystems

Abstract In lotic ecosystems, a higher availability of allochthonous food resources is expected during floods and rainfall events, which may yield a higher consumption of these resources by consumers. However, allochthonous input and seasonality in environmental conditions are locally dependent. Thus, dietary responses of freshwater consumers to seasonality should also be locally dependent. Herein, we applied a meta‐analytical approach to identify the spatial and seasonal environmental variables associated with the relative consumption of allochthonous food resources by fishes from tropical lotic ecosystems in different seasons. We gathered 566 observations of the diet of fish populations (i.e., restricted to the same sampling event) from 38 studies conducted in 70 localities across the tropics during flood and drought periods (hereafter, high‐water and low‐water periods, respectively). We retrieved latitude, seasonal channel width, elevation and two proxies for allochthonous input for each locality: terrestrial biomass (without considering seasonality) and the normalised difference vegetation index (NDVI; considering seasonality). Then, we applied meta‐regression models using these environmental variables as predictors and the proportion of allochthonous food resources in each consumer's diet (%Allo) as the response variable. Our models revealed that the diet of fishes from tropical lotic ecosystems is mostly autochthonous‐based, independent of the hydrological period (high‐water or low‐water), and aquatic invertebrates were the most consumed food items. Terrestrial vegetation biomass and elevation predicted increasing allochthony in the diet of tropical fishes for high‐water, but only terrestrial biomass predicted allochthony at low‐water periods. We found no relationship between latitude, channel width or NDVI with allochthony. Our study highlights the importance of considering the hierarchical level of biological organisation and fish trophic guilds for understanding seasonal patterns of relative consumption of allochthonous and autochthonous food resources by fishes. We also argue that variations in seasonality across the tropics are likely to have undermined its influence on allochthony in fish diets. The absence of a non‐relationship between channel width and allochthony provides evidence that the River Continuum Concept is better suited to temperate lotic ecosystems. Our results provide novel insights and the big‐picture of seasonal pattern in the diets of tropical fishes for use in future local empirical studies, improving forecasting of the relationship between the factors underpinning the availability of allochthonous and autochthonous food resources, and the diet of freshwater fishes.

Dietary garden cress (Lepidium sativum) seeds mitigate the effect of aflatoxin B1 contamination on growth, antioxidant status, AFB1 residues, immune response, and tissue architecture of Oreochromis niloticus

The contamination of fish diets with aflatoxin B1 (AFB1) poses a significant hazard to the aquaculture sector. This study investigates the efficacy of supplementing Nile tilapia (Oreochromis niloticus) diets with garden cress (Lepidium sativum) seeds (GCS) to mitigate the adverse effects of AFB1. For this purpose, a factorial design was utilized, consisting of a 2×3 arrangement of treatments. This included two contamination levels of AFB1: (0 and 2 mg kg−1 diet). Within each contamination level, three dietary levels of GCS were used (0 %, 1 %, and 2 %). The study involved 270 healthy O. niloticus with an average weight of 25.14 ± 0.39 g (45 fish/group and 15 fish/replicate). The duration of the trial was 60 days. The study evaluated growth performance, hematological indices, hepatorenal function, immune and antioxidant indicators, histomorphology of organs, AFB1 residues in muscles, and fish resistance to Aeromonas hydrophila. The results indicated that GCS dietary supplementation significantly counteracted AFB1-induced growth retardation and reduced fish survival. Additionally, GCS effectively reversed the anemia, leukopenia, hypoproteinemia, hypoalbuminemia, and hypoglobulinemia that were produced by AFB1. Moreover, GCS dietary supplementation significantly suppressed the AFB1-induced increase in serum bilirubin, hepatic enzymes, kidney damage products, cortisol, and glucose. Additionally, the inclusion of GCS in the fish's diet effectively eliminated the accumulation of AFB1 in their muscles. Moreover, GCS supplementation demonstrated significant restoration of depleted antioxidant and innate immune components induced by AFB1. Furthermore, GCS significantly reduced the degenerative changes in renal, hepatic, splenic, and small intestine tissues caused by AFB1. Fish fed a GCS-fortified diet and exposed to AFB1 displayed restored disease resistance when challenged with A. hydrophila. In conclusion, supplementing Nile tilapia diets with GCS at 2 %, even in the presence the AFB1 contamination, significantly enhanced the fish growth, improved health, and increased disease resistance while reducing AFB1 residues, thereby benefiting consumer health.

Growth performance, hematological profile, and related genes expression in goldfish (Carassius auratus) fed on rosmarinic acid-enriched diets and subjected to ambient ammonia

Recently, supplementing fish diets with polyphenols has attracted more attention because of their great nutritional role. The unionized ammonia is one of the critical water parameters that adversely affects the fish performance and welfare status. Hence, the present perspective outlines the potential value of dietary rosmarinic acid (RA) in boosting growth, hematological, and immune biomarkers, besides related-genes expressions post-exposure of goldfish (Carassius auratus) to ambient ammonia. Fish (n = 240) were separated into four groups; RA0 (the control), RA400, RA600, and RA800 received 0, 400, 600, and 800 mg RA/kg feed, respectively. After 56 days, counts of white and red blood cells and growth indices (weight gain, specific growth rate, feed intake, and feed conversion ratio) were evaluated. After that, the fish per each treatment were exposed to 0.5 mg/L of unionized ammonia for three hours. After the challenging time, many biomarkers were measured including immune response (ACH50, total immunoglobulin, and lysozymes activity), digestion (proteases activity), and genes expression involving MUC, HSP27, HSP30, HSP47, TNFa, Lp1, and Fas genes plus the anti-inflammatory cytokines (IL6, IL8, and IL10). The findings of the current research revealed that dietary RA intervention fostered growth performance, improved blood picture (p < 0.05), and enhanced (p < 0.05) the expression of genes, which are responsible for modulating immunity and anti-inflammatory status in a dose-dependent manner. The present study concluded that dietary RA is a successful natural feed supplement for goldfish with an optimal level of 600 mg RA/kg feed. However, it verifies antitoxic and anti-inflammatory properties against ambient ammonia toxicity. It also has a promising influence on the growth, hematological, and immunity and anti-inflammatory related genes expression of goldfish, C. auratus.

Possible beneficial effects of nano chitosan against doxycycline toxicity in Nile tilapia (Oreochromis niloticus)

In aquaculture, improper and illogical antibiotic use could yield negative outcomes. Therefore, this study investigates the ameliorative effects of chitosan (CS) and chitosan nanoparticles (CSNPs) against the toxicity of the antibiotic doxycycline in Nile tilapia fish. The fish were divided into four distinct categories: the first group served as the control, the second group was subjected to doxycycline (40 mg/L), the third group experienced doxycycline (40 mg/L) and CS (0.5% in fish diet), and the fourth group was exposed to doxycycline (40 mg/L) with CSNPs (0.5% in fish diet) for 15 days. Levels of creatinine, uric acid, and aspartate aminotransferase activities notably elevated (p < 0.05) in the doxycycline-treated group when compared with the control group. Meanwhile, fish in the doxycycline-exposed group demonstrated significantly lower (p < 0.05) levels of red blood cells, hemoglobin, packed cell volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and neutrophils. Conversely, mean corpuscular volume, platelets, white blood cells, and lymphocytes exhibited notably higher (p < 0.05) levels in the doxycycline group. Other hematological indicators, including monocytes and eosinophils, showed no notable variances (p > 0.05) among the studied groups. Fish treated with doxycycline exhibited notably higher (p < 0.05) interleukin-1β and interleukin-6 activity in comparison to the control group. Additionally, histopathological changes were detected in the gills, liver, and kidney tissues of doxycycline-exposed fish when contrasted with the control group. Co-exposure of CS and CSNPs significantly restored most hematological, biochemical, and immunological parameters, as well as histopathological indices, in the fish, aligning these values closer to those observed in the control group in comparison to the fish treated solely with doxycycline. In conclusion, both CS and CSNPs played an important role in moderating the negative effects of doxycycline on fish, through improving hematological indices, reductions in creatinine, uric acid, and aspartate aminotransferase activity, as well as anti-inflammatory action through reductions in interleukin-1β and interleukin-6 activity.