Experimental Fish Research Articles

Organ-specific bioaccumulation of microplastics in market fish of Dhaka and size-dependent impacts of PVC microplastics on growth of Anabustestudineus

Microplastics (MPs), a growing environmental concern with potential ecotoxicological risks, are ubiquitous in aquatic environment. This study investigated the organ-specific distribution and variation of MPs in commercially caught fishes (7 species, 140 individuals) collected from Dhaka's two main fish distribution hubs (Uttara and Jatrabari). Additionally, the impact of different-sized MPs on fish growth (Anabas testudineus) was examined in a control experiment. Results revealed that kidneys of market fish bioaccumulated the highest concentration of MPs (average, 59.1 MPs/g), followed by liver (24.6 MPs/g) and intestine (18.6 MPs/g). On average, fish from Uttara had a higher MPs concentration (36 MPs/g) compared to Jatrabari (25 MPs/g). Among fish species, Glossogobius giuris showed the highest MPs bioaccumulation due to its feeding habits and morphology. Fiber-shaped MPs were most prevalent in all fishes (79–93%) except Glossogobius giuris (fragments, 51%). Fourier-transform infrared spectroscopy (FTIR) analysis identified 19 different polymer types, with high density polyethylene (HDPE), ethylene vinyl acetate (EVA) and polyamide (PA) being commonly found in all organs. The experimental study confirmed that large-sized PVC MPs (1.18 mm-300 μm) had a greater negative impact on fish growth (length) and caused more physical deformities (particularly intestinal injuries) compared to small-sized PVC MPs (150 μm–75 μm). Moreover, fish exposed to larger diameter MPs experienced highest physical weight and depth loss among exposed groups. Large-sized PVC MPs bioaccumulated highest in fish compared to small-sized PVC MPs. Similar to market fish, kidney in the experimental fish had the highest MPs bioaccumulation (6.5 MPs/g), followed by liver (5.2 MPs/g) and intestine (4.8 MPs/g), with a dominance of fibers despite the presence of high concentration of fragments in the food source. Statistical analysis also supported a clear correlation between increasing MPs size and adverse effects on fish growth and health. Urgent action is needed to curb microplastic pollution and protect ecosystems and human health.

Immune protective, stress indicators, antioxidant, histopathological status, and heat shock protein gene expression impacts of dietary Bacillus spp. against heat shock in Nile tilapia, Oreochromis niloticus

This research evaluated the efficacy of mixed Bacillus strains probiotic supplements in mitigating acute thermal-induced stress in Nile tilapia (Oreochromis niloticus). Three experimental fish groups involved 135 Nile tilapia (49 ± 2 g); one control (no added probiotics), 0.5, and 1% of selected Bacillus strains (B. subtilis, B. licheniformis, and B. pumilus) for 58 days. After the feeding period, growth parameters, immunological parameters, stress biochemical markers, and antioxidant parameters in addition to genes related to stress and histopathological changes in fish, were assessed; subsequently subjected to heat shock at 36 ± 0.5 ◦C for 2 h. Before the heat challenge, our results exhibited a marked increase in the growth efficacy (P < 0.05), lower marked serum levels of triglycerides and cholesterol, and tissue malondialdehyde (MDA) levels along with significantly increased superoxide dismutase (SOD) and catalase (CAT) enzymes activity in fish-fed Bacillus probiotic at 0.5% concerning the control group (P < 0.05). There were no significant changes in the serum levels of glucose, cortisol, lactate, phagocytic activity, respiratory burst (ROS), total immunoglobulin Ig, alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), total protein, albumin, globulin, uric acid, urea, creatinine, as well as HSP70, GST, and GPx mRNA expression in most of the probiotic groups compared to the control group (P > 0.05). When Nile tilapia was exposed to heat stress, supplementation with Bacillus probiotic in the diet significantly decreased most of the indices related to serum biochemical (ALT (P < 0.01; P < 0.001), AST (P < 0.01), LDH (P < 0.01), urea (P < 0.05), and creatinine (P < 0.01)), triglycerides (P < 0.001; (P < 0.01)), cholesterol (P < 0.01; (P < 0.05)), glucose (P < 0.001), and cortisol (P < 0.01; (P < 0.05)), with tissue oxidative stress MDA levels (P < 0.05), and HSP70 mRNA expression (P < 0.01; P < 0.001), aligned with the stressed control group. In addition, a notable upsurge in the total protein, albumin, globulin, phagocytic and ROS activities, and total Ig, as well as the enzymatic antioxidant ability (SOD, CAT) (P < 0.01), with GST and GPx mRNA expression (P < 0.05; P < 0.01), were shown in fish-fed Bacillus spp. post-exposure compared with the stressed control group. Besides, no histopathological alterations were revealed in the spleen and brain of fish pre- and post-heat exposure. According to our findings, diet supplementation of Bacillus species has the potential to combat the suppressive effects of heat shock in Nile tilapia.

Comparison of catch efficiency of wire mesh fish traps operated along the coast of Thoothukudi, South-east coast of India

Aim: The study designs and fabricates traps with diverse wire mesh colors and shapes for field experiments. It also collects detailed catch data to assess their catch efficiency and determine the most effective design. Methodology: Experimental fish traps were fabricated utilizing four distinct colors (Light green, Dark green, White and Orange) and three different shapes (rectangle, square and circle). Fishing trials were conducted in selected fishing villages of Thereshpuram, with the traps operated fortnightly from June 2022 to May 2023. The catch rate per trip (CPUE) was calculated using the Total catch (in numbers) divided by the Unit Effort (White, 1987). An economic analysis of trap fishery was also performed based on gross revenue and total cost (Geetha et al., 2014). Results: The traps' overall catch per unit effort (CPUE) was recorded at 0.48Nos hr-1. Siganus canaliculatus emerged as the dominant species among the fishes trapped, constituting 16% of the total catch. Regarding trap color, the highest CPUE was observed with traps of dark green color (0.63 Nos hr-1), followed by light green (0.51 Nos hr-1), white (0.49 Nos hr-1) and orange (0.38 Nos hr-1). Economically, the performance of the trap fishery was evaluated using indicators such as operating cost/year, fixed cost, gross revenue and profit cost ratio. The success of the trap fishery was further emphasized by a benefit-cost ratio (BCR) of 3.50. Interpretation: Dark green-colored, square-shaped traps show promise in significantly enhancing fishermen's profits due to their higher catch per unit effort (CPUE) compared to other colors. Moreover, dark green traps may offer ecological advantages by blending into natural surroundings. This study highlights their potential and provides practical insights for fishermen to make informed gear choices, considering factors like color and shape. Key words: BCR, Color, CPUE, Shape, Trap

The Effect of Phytase Enzyme in Feed on Growth Performance, Feed Utilization Efficiency, and Survival Rate of Milkfish (Chanos chanos) Fingerlings

The aim of this study was to evaluate the effect of phytase enzyme supplementation on the growth performance, feed utilization efficiency, and survival rate of milkfish fingerlings. The experimental fish used in this study were milkfish fingerlings with an average weight of 2.89±0.46 g per fish. The feed used in this research was a formulated pellet feed containing 30% protein, with added phytase enzyme. The treatments consisted of different phytase enzyme doses, namely A (0 mg/kg feed), B (250 mg/kg feed), C (500 mg/kg feed), and D (750 mg/kg feed). The results showed that different doses of phytase enzyme in the feed significantly affected (P&lt;0.05) growth performance and feed utilization efficiency but did not significantly affect (P&gt;0.05) the survival rate of milkfish fingerlings. The optimal dose of phytase enzyme for improving growth performance and feed utilization efficiency in milkfish fingerlings was between 502-665 mg/kg feed, resulting in a maximum total feed consumption (TFC) of 140.43 g, Feed Conversion Ratio (FCR) of 1.18, feed efficiency (FE) of 78.16%, protein efficiency ratio (PER) of 2.6, and relative growth rate (RGR) of 4.43%.

Effect of water pollution by nickel on hepatic enzymes and oxidative enzymes in Cyprinus carpio (common carp)

Nickel (Ni) is considered a toxic heavy metal that causes serious diseases in humans and animals. Therefore, this study was conducted on common carp, which is considered an essential food item for humans. This study was designed to investigate the effect of nickel on the hepatic and antioxidant enzymes of Cyprinus carpio after 3 and 6 weeks of exposure to water contaminated with Ni. C. carpio fingerlings were purchased from a neighboring fish hatchery. The morphometric characteristics of the experimental fish were documented. All fish were stocked, regardless of gender. The fish were exposed to different concentrations (20, 40, 60, 80, and 100 mg/L) to obtain the LC50 for Ni during 96 hours, and the median lethal concentration of Ni was 80 mg/L through 96 hours. The fish were exposed to two safe concentrations, 1 ppm and 5 ppm. The results after 3 and 6 weeks were as follows: When compared to the control groups, all treated groups had significantly higher levels of liver function parameters (ALT and AST). Malondialdehyde (MDA) and catalase activity measurement (CAT) enzyme levels were considerably higher in all treated groups after 3 and 6 weeks as compared to control groups. These changes are trustworthy indications of the cellular and humoral immune responses in C. carpio.

Preparation of Platinum Nanoparticles of Biophytum reinwardtii and Evaluation of Neuroprotective Activity of MPTP-induced Parkinson’s Disease in Zebra Fish

Aim: To evaluate the Neuroprotective activity of Biophytum reinwardtii Platinum nanoparticles Methods: Biophytum reinwerdtii platinum nanoparticles were subjected to evaluation of the neuroprotection activity in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine induced zebra fishes. Experimental fishes are divided into 5 groups, each containing 8 fishes. Group I is considered a normal group; Group II is a toxic group means treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine 225 mg/kg, i.p. for 5 days; Group III, IV, and V are treatment groups means treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (225 mg/kg) with 0.3 µmol, 0.4µmol, and 0.5 µmol of Biophytum reinwardtii Platinum nanoparticles respectively for 5 days. Results: In the in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine group, locomotor activity and complex I activity are decreased, Malondialdehyde levels increased, antioxidants, and catecholamines levels decreased, whereas Biophytum reinwardtii Platinum nanoparticles treated fishes exhibit significant locomotor and increased levels of antioxidants and catecholamines. Conclusion: These results suggest that Biophytum reinwardtii Platinum nanoparticles. Showed significant neuroprotection activity in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine -induced Parkinson’s zebra fishes.

The use of protein hydrolysate from fish waste as part of microbiological culture media

The need to involve in the processing of significant amount of secondary protein-containing raw materials formed during fish cutting, on the one hand, and on the other hand, the shortage of a source of the protein component of microbiological nutrient media determines the relevance of the work. The goal was to study the possibility of using fish protein hydrolyzate obtained by enzymatic hydrolysis from secondary fish raw materials in microbiological nutrient media. Microbiological and physicochemical methods were used to conduct research. When optimizing the developed algorithm for the fermentation process, a mathematical model of the experiment was used with a minimum number of experiments. An algorithm has been developed for obtaining fish protein hydrolyzate from meat and bone waste from cutting pelagic fish (cod). The hydrolysis parameters were optimized: the concentration of the enzyme preparation is 1.33 % of the total mass of waste, the duration of the fermentation process – 3 hours. The characteristics of the resulting fish hydrolyzate are determined: the mass fraction of total nitrogen – 13 %, amine – 3.6 %, water – 4.6 %, sodium chloride – 2.7 %, fat – 0.3 %. An experimental fish hydrolyzate has been studied as a source of protein nitrogen in accordance with the formulation of a microbiological medium used for counting when growing colonies of microorganisms. The effectiveness of the prepared nutrient media was assessed by comparing the performance coefficients of the experimental and control nutrient media, as well as by identifying test microorganisms grown on the experimental medium. It was established that the growth pattern of test cultures both on the studied nutrient medium and on the control medium was almost the same. Test microorganisms retained their biochemical, morphological and cultural characteristics. The research results showed the possibility of using fish protein hydrolyzate obtained by enzymatic hydrolysis from secondary fish raw materials in microbiological nutrient media.

Ameliorating effects of natural herbal supplements against water-borne induced toxicity of heavy metals on Nile tilapia, (Oreochromis niloticus)

The efficacy of herbal supplements in mitigating heavy metals (HMs) toxicity was investigated using a widely grown fish, the Nile tilapia (Oreochromis niloticus). The experiment was conducted over two phases: during the stress phase, the experimental fishes were exposed to sub-lethal concentrations of HMs, including lead, cadmium, zinc, and copper for 15 days; following which during the feeding phase, herbal supplements were given for 70 days to ameliorate their effects. Seven groups were established: the control negative group (CON−ve), control positive group (CON+ve, without any treatment), and five groups with supplementation of 1% turmeric (TUR), cinnamon (CIN), ginger (GIN), garlic (GAR), and their mixture (MIX), respectively. A total of 315 fishes were distributed evenly in experimental tanks (15 fishes per tank, in triplicates). The results revealed that exposure to HMs led to significant (p < 0.05) alterations in all the tested parameters, i.e., liver damage and growth reduction. The herbal supplements, especially the MIX groups, ameliorated the harmful effects of HMs and restored fish growth, digestibility, carcass composition, and liver health. In conclusion, the study demonstrated that the herbal supplements were effective in reducing the HMs-linked toxicity in Nile tilapia. Future studies pertaining to the mechanisms facilitated by the various herbal bioactive substances-linked tolerance to HMs in fishes are warranted.

A Study on the Catch Losses and Mesh Selectivity Related to the Attachment of Marine Mammal Bycatch Reduction Devices on Midwater Trawl Gear

The National Institute of Fisheries Science in Korea is developing marine mammal bycatch reduction devices (BRDs) for high-risk fishing gear, such as trawls. We experimented with two BRD types (guiding nets) attached in front of codend at 30° and 45° angles, and catch losses and mesh size selectivity were investigated. Experimental fishing operations were conducted along the East Coast of South Korea where whales and dolphins are commonly sighted. The catch was classified according to fishing location, BRD type, codend, and covernet, with measurements recorded for body length, maximum girth, and weight. The average selectivity for each haul was analyzed using the ‘selfisher’ package. The catch loss rates with the BRD attached at tilt angles of 30° and 45° were 11% and 29% for common flying squid, 6% and 28% for sailfin sandfish, and 5% and 8% for pearlside. While the mesh selectivity rates for common flying squid and pearlside remained at 0.2–0.5 across all lengths and tilt angles, the mesh selectivity curve for sailfin sandfish was estimated. There were significant differences in catch loss between 30° and 45° angles, with the 30° angle being more effective in catch loss. We observed a masking effect in the codend.

Spectral-based detection of chromatin loops in multiplexed super-resolution FISH data

Involved in mitotic condensation, interaction of transcriptional regulatory elements and isolation of structural domains, loop formation has become a paradigm in the deciphering of chromatin architecture and its functional role. Despite the emergence of increasingly powerful genome visualization techniques, the high variability in cell populations and the randomness of conformations still make loop detection a challenge. We introduce an approach for determining the presence and frequency of loops in a collection of experimental conformations obtained by multiplexed super-resolution imaging. Based on a spectral approach, in conjunction with neural networks, this method offers a powerful tool to detect loops in large experimental data sets, both at the population and single-cell levels. The method’s performance is confirmed on experimental FISH data where Hi-C and other loop detection results are available. The method is then applied to recently published experimental data, where it provides a detailed and statistically quantified description of the global architecture of the chromosomal region under study.

Oral administration of recombinant Lactococcus lactis expressing largemouth bass (Micropterus salmoides) IFNa3 protein enhances immune response against largemouth bass virus (LMBV) infection

Largemouth bass virus (LMBV) is a highly pathogenic pathogen that often causes high mortality of affected largemouth bass and significant financial losses. Type I interferon as an effective and broad spectrum tool has been successfully used for therapeutic or prophylactic treatment some viral infections. However, the implementation of immunotherapies based on interferon administration to combat LMBV infections has not been reported. And Lactic Acid Bacteria (LAB) are a powerful vehicle for expressing cytokines or immunostimulant peptides at the gastrointestinal level after oral administration. In this study, Lactococcus lactis (L. lactis) expression system with lactose as a screening marker was utilized to express the Micropterus salmoides interferon a3 (IFNa3) protein and orally administered to largemouth bass. The genetically engineered strain pNZ8149-Usp45-IFNa3-6His/L. lactis NZ3900 was successfully constructed, and its potential to elicit immune protection response by oral administration was evaluated. After orally administration, the recombinant L. lactis was detected in guts of experimental fish and remained detectable for 72 h. Additionally, IFNa3 was able to enhance the test fish's immune response, as determined by the relatively increased mRNA relative expression of immune-related genes in the liver, spleen, and kidney tissues, including IFN-γ, TNF-α, IL-1β, IL-8, IgM and IgT. Following LMBV challenge, the experiment group of pNZ8149-Usp45-IFNa3-6His/L. lactis NZ3900 exhibited a 70 % survival rate, while survival rate were 15 % in the PBS control group, 45 % in the pNZ8149/L. lactis NZ3900 group. Furthermore, the viral load in the surviving fish was significantly lower than that of the control groups. These findings suggest that oral administration of recombinant L. lactis producing IFNa3 induces largemouth bass immune responses at a systemic level to effective prevent and combat of LMBV infection.

Spatio-temporal Dynamics of Anuran Populations in the Wetlands of Korhogo, Côte d'Ivoire

Aims: The Korhogo commune contains several natural habitats that are home to a large community of frogs. But today, these habitats are facing strong anthropic pressures. This study aims to show the effect of anthropogenic activities on wetlands and the organisms that live there. Methodology: Sampling took place from June 2023 to May 2024, and samples came from experimental fishing using deep-net dip nets with 2 mm mesh or rod and line, and from commercial fishing using various gears. Results: A total of 791 individuals were caught, for a total biomass of 48.872 Kg. These individuals were divided into 5 species, 4 genera and 4 families. Spatially, diversity was highest in the lakes (80) and lowest in the rice fields (20%). Temporally, diversity was highest in the rainy season (100%) and lowest in the dry season (40%). The species Hoplobatrachus occipitalis dominated the population with 94.66% of captures. It accounted for 25.46%, 24.27%, 22.81%, 13.93% and 13.53% respectively in lakes, rice fields, rivers, wells and shallows. The strong presence of this species in the wetlands of this commune shows that these areas are highly threatened. Conclusion: This study contributes to the knowledge of the frog population and helps to combat the degradation of wetlands in the city of Korhogo.

The New Fishing Technique With Lighted Gillnets in Lake Kivu: Panacea or Pandora's Box?

ABSTRACTA new fishing technique has been introduced in Lake Kivu, across the Congo side. It consists of gillnets on which light‐emitting diode (LED) lamps are attached. Traditional fishermen have introduced the fishing technique without any studies related to the positive and drawback effects of this fishing technique. We sought to understand whether the gillnets with LED lamps fishing technique improve fishing catches and can be regarded as sustainable for the Lake Kivu ecosystem, or is it just only a marketing strategy for gillnets and LED lamp sellers. Two complementary approaches have been used in this study. Experimental fishing campaigns were conducted from June 2021 to June 2022 and monitoring of fishing team in the field coupled with surveys of fishermen about the effectiveness use of this new fishing technique. We observed that (i) 88% of fishermen using gillnet in the Bukavu sub‐basin have already adopted the recently introduced fishing technique; (ii) the average catch per unit effort of gillnets with LED lamps is higher than those without LED lamps (3.84 ± 1.95 kg/net vs. 2.69 ± 2.04 kg/net); (iii) these gillnets retrieve larger specimens (79.88 mm vs. 76.69 mm) and generate monthly a higher average profit to fishermen ($916.35) than the fishing technique lacking the LED ($807). However, (iv) the gillnets with LED lamps generates a lot of plastic trash: around 2130 kg of plastic bags/month under fishing conditions in the Bukavu sub‐basin. So, this new fishing technique is a real panacea for its practitioners, but a veritable Pandora's box generating plastic pollutants in Lake Kivu. Instead of banning this new fishing technique, we need to adapt it by using submersible LED lamps.

Integrating Direct Experimental Fishing and Environmental DNA Metabarcoding to Assess Fish Biodiversity in the Cibareno River, Indonesia, to Support Fishway Design

Integrating Direct Experimental Fishing and Environmental DNA Metabarcoding to Assess Fish Biodiversity in the Cibareno River, Indonesia, to Support Fishway Design

Evaluation of visible implant elastomer (VIE) tags for use in supplementation of an endangered estuarine fish

AbstractObjectiveDelta Smelt Hypomesus transpacificus are thought to be close to extinction in the wild, which has spurred multiagency conservation efforts to supplement their population. In conjunction with these recent efforts, monitoring is needed to assess the effectiveness of supplementation. Such monitoring often uses large‐scale tagging of released fish to distinguish between hatchery‐origin and wild‐origin fish that are captured during later surveys.MethodsIn this study, we evaluated the use of visible implant elastomer tags in Delta Smelt to determine whether fish survival, fish growth, or tag retention were dependent on (1) tag color (blue, green, orange, red, yellow, and no‐tag control) or (2) tagged body location (posterior‐dorsal, anterior‐dorsal, mid‐lateral line, and no‐tag control).ResultOver 165 days of the first experiment, there was no difference in growth rate (mean = 0.073 mm/d, range = 0.072–0.075 mm/d) or survival (mean = 68%, range = 63–77%) among tag colors. Across all color groups, mean tag retention was 96% (range = 87–100%). Over 120 days of the second experiment, tag location had no influence on fish growth rate (mean = 0.064 mm/d, range = 0.062–0.067 mm/d) or survival (mean = 50%, range = 43–58%). For the surviving fish in experiment 2, the tags that were placed at the mid‐lateral line were retained less (84% on day 120) than those at posterior‐dorsal and anterior‐dorsal locations (99% and 98%, respectively).ConclusionOur results suggest that visible implant elastomer tagging is a suitable method for marking adult Delta Smelt (&gt;50 mm fork length) for up to 165 days and can be useful for conservation monitoring efforts.

Physio-metabolic alterations in Labeo rohita (Hamilton, 1822) and native predator Chitala chitala (Hamilton, 1822) in presence of an invasive species Piractus brachypomus (G. Cuvier, 1818).

A 60days study was conducted to evaluate the physiological response of indigenous species Labeo rohita (LR) and indigenous predator Chitala chitala (CC) in presence of an invasive species Piaractus brachypomus (PB). Two treatment groups as LR + PB (T1) and LR + PB + CC (T2) with individual control groups as T0LR, T0PB and T0CC were designed in triplicates. Fingerlings of LR, PB and CC were randomly distributed into 15 circular tanks with a stocking ratio of 1:1 and 1:1:0.3 in T1 and T2 group, respectively and 10 nos. each of LR, PB and CC in respective control groups. At first 15min of the experiment, cortisol level was found significantly (P < 0.05) higher in all three experimental fishes in T1 and T2 groups. With the experimental duration, the level of stress hormone (cortisol), oxidative stress enzymes (superoxide dismutase, catalase, and glutathione peroxidase), tissue metabolic enzymes (lactate dehydrogenase and malate dehydrogenase), serum metabolic enzymes (transaminase enzymes) and blood glucose level were significantly (P < 0.05) increased in T1 and T2 groups for LR and CC whereas, no variation (P > 0.05) were observed for PB in both T1 and T2 groups. The total antioxidant capacity (TAC), liver glycogen, total protein, albumin and globulin were found to be significantly (P < 0.05) decreased in LR in the presence of PB and CC. The present study provides a preliminary insight into the biological interaction between native and invasive species and their physiological responses in the presence of native predator with higher trophic index. Thus, the results of the study suggest the superior traits of invasive P. brachypomus try to dominate the other two native species by negatively influencing the native fauna even with a higher trophic index (C. chitala).

Analysis of bamboo fibres and their associated dye on a freshwater fish host-parasite system

With the growth of the fashion and textile industries into the twenty-first century, associated pollution has become pervasive. Fibre-based microplastics are the most common types of plastics recovered from aquatic ecosystems encouraging the move towards organic fibre usage. Often marketed as biodegradable and ‘environmentally friendly’, organic textile fibres are seen as less harmful, but their impacts are understudied. Here, we assess the health effects of reconstituted bamboo-viscose fibres, processed bamboo-elastane fibres (both at 700 fibres/L) and their associated dye (Reactive Black-5, at 1 mg/L) on fish, with an emphasis on disease resistance utilising an established host-parasite system: the freshwater guppy host (Poecilia reticulata) and Gyrodactylus turnbulli (monogenean ectoparasite). Following 3 weeks exposure to the bamboo fibres and associated dye, half the experimental fish were infected with G. turnbulli, after which individual parasite trajectories were monitored for a further 17 days. Overall, exposures to reconstituted bamboo-viscose fibres, processed bamboo-elastane fibres or dye were not associated with any change in host mortality nor any significant changes in parasite infection burdens. When analysing the routine metabolic rate (RMR) of fish, uninfected fish had, on average, significantly impacted RMR when exposed to processed bamboo-elastane (increased RMR) and reconstituted bamboo-viscose (decreased RMR). Hosts exposed to reconstituted bamboo-viscose and the associated dye treatment showed significant changes in RMR pre- and post-infection. This study bolsters the growing and needed assessment of the potential environmental impacts of alternative non-plastic fibres; nevertheless, more research is needed in this field to prevent potential greenwashing.

The effects of using hydrolyzed feather meal, amino acids, and probiotics in the diet of juvenile rainbow trout on growth, digestibility, and expression of growth-related genes

The study investigated the effect of replacing fishmeal by varying levels of hydrolyzed feather meal (HFM) as well as dietary probiotic supplementation on growth performance, digestibility, histology, and gene expression of juvenile rainbow trout (Oncorhynchus mykiss). Five iso-nitrogenous (average of 50.60% crude protein), iso-energetic (average of 21.79 kJ/g), and iso-lipidic (average of 21.86% crude lipid) diets were formulated and fed to triplicate groups of juvenile rainbow trout weighing 29.65 ± 0.39 g (mean ± SD) for 75 days. Dietary treatments included one control (50% fishmeal) and four experimental diets, each containing 2 g/kg probiotics (Lactobacillus plantarum and Bacillus subtilis). The experimental diets included HFM30 (150 g/kg HFM, 9 g/kg lysine, and 4 g/kg methionine), HFM35 (175 g/kg HFM, 11 g/kg lysine, and 5 g/kg methionine), HFM40 (200 g/kg HFM, 13 g/kg lysine, and 6 g/kg methionine), and HFM45 (225 g/kg HFM, 15 g/kg lysine, and 7 g/kg methionine). Up to 40% replacement of fishmeal with HFM showed no significant difference compared to control group in growth performance (P > 0.05). Feed utilization of HFM45 was slightly lower than control and all the other experimental groups. There was no statistically significant difference in FCR value between HFM40 and control groups (P > 0.05). The apparent digestibility coefficients (ADCs) for protein and amino acids were very high in all groups (P < 0.05). Intestinal mucosa and sub‐mucosa layers of experimental fish showed general tissue integrity with no signs of tissue necrosis. For intestinal morphology, where 45% HFM replacement was applied, villus length to crypt depth (VL to CD) and villus surface area (SA) decreased by 46.01% and 44.44%, respectively, compared to the control group (P < 0.05). This situation shows that intestinal morphology can be damaged when the highest level (HFM45) of feather meal is used. Dietary HFM upregulated growth-related genes such as IGF-II, IGFBP-1b, IGFr1a, GDF9, and FGF2 and downregulated GHR-I and IGF-I. Overall, inclusion of HFM at 40% showed similar results to control group in juvenile rainbow trout feeding.

Partial fishmeal replacement by soybean meal induces fish growth retardation and gut inflammation via gut mucosal barrier dysfunction and dysbiosis in largemouth bass

The study aimed to investigate the effect of partial fishmeal replacement by soybean meal on fish growth, gut histology, oxidative stress, gut microbiota, and gene expression of inflammatory cytokines and tight junction proteins in largemouth bass (Micropterus salmoides). Four isonitrogenous and isolipidic diets were formulated: the FM diet contained 45 % fishmeal (FM diet) and did not contain soybean meal; diets SM25, SM50, and SM75 replaced 25 %, 50 %, and 75 % fishmeal protein in the FM group with soybean meal, respectively. Experimental fish (4.3 ± 0.1 g) were fed to apparent satiation for eight weeks. The results showed that replacing 25 % or more fishmeal decreased villus height, villus width, total superoxide dismutase (T-SOD) and catalase (CAT) activity levels, reduced glutathione contents, and Aurantimicrobium abundance; increased malonaldehyde contents and tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β) expression; downregulated nuclear factor E2-related factor 2 (Nrf2), occludin, and zona occluding-1 (ZO-1), lysozyme (LYS) and hypoxia-inducible factor-1α (HIF-1α) expression, compared with FM (P < 0.05). Moreover, SBM50 and SBM75 decreased final body weight, weight gain rate, and specific growth rate, and increased the lamina propria width than FM (P < 0.05). Furthermore, SBM25 dramatically reduced Actinobacteriota, Enterococcus, Lactococcus, Leuconostoc, and Streptococcus abundance (P < 0.05). Compared to SM25, SM75 dramatically increased Brucella abundance (P < 0.05). Pearson correlation analysis indicated that tight junction proteins (ZO-1 and Occludin) and gut microbiota (Aurantimicrobium and Brucella) have a significant association with gut inflammation and fish growth (P < 0.05). These results showed that gut dysbiosis and intestinal mucosal barrier dysfunction are major contributors to the soybean meal-induced growth retardation and gut inflammation in fish.

Intestinal microbiota was closely related to feed efficiency of Larimichthys crocea fed two fishmeal-free diets

This study examined the link between feed efficiency (FE) and intestinal microbiota in Larimichthys crocea fed on fishmeal-free diets. Two types of fishmeal-free diets were formulated: a plant protein-based feed (Group P) and a mixed-protein feed (Group M). These two types of diets were utilized to rear the two groups of L. crocea for 28 days, each consisting of individuals that were 18 months old. Initial and final weights, as well as feed consumption, of the experimental fish were documented. FE was calculated for each fish based on this data. Post-experiment, samples were taken from fish with high and low FE for 16S rRNA gene sequencing. In the Group M, the high and low FE fishes were designated as MH (proximal intestine, MHp; distal intestine, MHd) and ML (proximal intestine, MLp; distal intestine, MLd). In the Group P, the high and low FE fishes were designated as PH (proximal intestine, PHp; distal intestine, PHd) and PL (proximal intestine, PLp; distal intestine, PLd). The results indicated that in Group M, there was no significant difference in microbial community structure between MH and ML, but the microbial diversity and species richness in MH were higher than that in the corresponding ML. MHp showed a significantly higher abundance of the orders Elsterales, Frankiales, and the family Hyphomicrobiaceae compared to MLp. MHd, in comparison to the MLd, had a significant higher abundance of the order Burkholderiales. There was also no significant difference in microbial community structure between PH and PL, but the microbial diversity in PH was lower than that in the corresponding PL. PHp showed a significantly higher abundance of Proteobacteria and GammaProteobacteria compared to PLp; whereas, the significant difference between PHd and PLd was only present in PLd. Microbial functional prediction analysis showed that the intestinal microbiota was mainly involved in carbohydrate metabolism, energy metabolism and vitamin metabolism pathways. These findings of this study contribute to our further understanding of the relationship between intestinal microbiota and the FE traits of the host. The microbial markers found between the high and low FE groups can offer insights and serve as a reference for subsequent research aiming to improve FE using Nutrition and Genetic Selection Techniques.