Aquaculture Research Articles

The Seasonal Variations in Hydrological Factors in the Activity Zones: An Essential Examination of the Ecosystem in Badagry Creek, Lagos, Nigeria

Abstract: The season is a pivotal representative in ascertaining the health status of a coastal ecosystem in a changing climate condition. The physico-chemical parameters of Badagry Creek were spatially and temporally investigated for twelve months (July 2017 to May 2018 for dry and wet seasons). Water samples were collected bi-monthly from nine stations, grouped into five activity zones during the water flow, covering upper, middle and lower courses. Seasonal variations in the physicochemical characteristics of Badgry Creek were found to be significantly different (<0.05) in salinity, phosphate, total suspended solids (TSS), total dissolved solids (TDS), depth, and dissolved oxygen (DO). Data were analysed using descriptive statistics, ANOVA and Spearman correlation at α₀.₀₅. The wet season had greater values of conductivity (551.27±79.09µS/cm; 412.77±42.7µS/cm) , pH (7.43±0.39: 7.41±0.41), salinity (5.04±1.11ppt: 1.22±0.40ppt), DO (6.72±0.26: 5.39±0.58mg/l), and chloride (Cl̉ˉ, 684.51±82.50 µmol/L: 674.22±73.44 µmol/L) than the dry season respectively. An increase in salinity during the wet season indicates the seawater intrusion and the waste discharge effluents from domestic and aquaculture processes into the stream from the higher course. Significant differences were observed between the Aquaculture (AQ) and Aquaculture combined Dredging (AQ_DG) zone for Sulphate and Chloride (Clˉ). The Biological Oxygen Demand (BOD) varied significantly between zones; they were 3.12±0.74mg/l in the Aquaculture zone (AQ) to 4.00±0.42 mg/l in the Domestic Waste (DW) zone and 2.10± 0.5 mg/l in the Aquaculture and Dredging (AQ_DG) zone to 19.2±9.44 mg/l in the Domestic Waste (DW) zone, respectively. The Highest value of TOM in DW station indicates anthropogenic effluents from domestic waste in this zone. The seasons were used to describe variations in Badagry Creek's physicochemical parameter values because the wet season noted higher parameter values, which may be related to an influx of water from the upper to the lower course.

SUSTAINABLE AQUACULTURE; ORGANIC INNOVATIONS FOR DISEASE PREVENTION AND HEALTH MANAGEMENT IN NILE TILAPIA (OREOCHROMIS NILOTICUS)

Sustainable aquaculture has become imperative in guaranteeing the enduring prosperity of aquatic farming, specifically for the Nile tilapia (Oreochromis niloticus), one of the most extensively farmed fish species. This study examines organic developments in Nile tilapia farming focused on eco-friendly practices that reduce the use of artificial chemicals and antibiotics to avoid sickness and maintain health. Integrating natural probiotics, probiotics, and immunostimulants into fish meals is one of the most critical tactics for strengthening the immune system and boosting the resistance of Nile tilapia against parasitic, bacterial, and viral infections. By maintaining the fish's natural defenses and promoting intestinal health, these natural additions lessen the need for conventional antibiotics. Moreover, the employment of beneficial microorganisms and biofiltration systems are two sustainable water management strategies that are essential for limiting the spread of illness in aquaculture settings. By emphasizing water quality through natural filtration processes, organic pond systems create a more balanced environment, lowering stress levels and disease susceptibility. By minimizing nutrient run-off, organic feed formulations using plant-based components, essential oils, and herbal extracts improve fish health and reduce the environmental effects of aquaculture techniques. This analysis also assesses these organic systems' economic viability, emphasizing how cost-effective and scalable they are compared to conventional aquaculture techniques. The aquaculture sector may minimize ecological impact while increasing fish health, producing better results, and adding to global food security through sustainable methods in Nile tilapia cultivation. To further advance sustainable aquaculture in the future, more studies are required to maximize these advances under various environmental circumstances and tilapia strains.

Behavioral dysregulation in Nile tilapia (Oreochromis niloticus, GIFT) post-Streptococcus agalactia infection: Role of the microbiota-gut-brain axis

In the aquatic farming industry, understanding the factors affecting fish behavior is crucial, particularly in response to infections that compromise welfare and productivity. Swimming performance is a key life history trait critical to their ecology. This study explores the swimming behavior imbalance in Nile tilapia (Oreochromis niloticus, GIFT) post-infection with Streptococcus agalactiae (GBS), a common pathogen responsible for significant losses in aquaculture. We focused on how the microbiota-gut-brain axis influences the behavioral response of tilapia to GBS infection. Behavioral changes were quantified by measuring collision times and swimming speeds, which decreased significantly following infection. This behavioral downturn is mediated by alterations in the microbiota-gut-brain axis, evidenced by increased levels of monoamine neurotransmitters (serotonin, norepinephrine, and dopamine) in the brain and intestinal tissues. The study utilized pharmacological agents, the 5-HT1A receptor agonist (8-OH-DPAT) and antagonist (WAY-100635), to investigate their efficacy in mitigating these behavioral and biochemical changes. Both agents partially restored normal behavior by adjusting neurotransmitter concentrations disrupted by GBS infection. Additionally, a notable increase in the relative abundance of Streptococcus within the gut microbiota of infected fish highlights the potential role of specific bacterial populations in influencing host behavior. This research provides novel insights into the complex interactions between pathogen-induced gut microbiota changes and Nile tilapia's behavioral outcomes, highlighting potential avenues for improving fish health management through microbiota-targeted interventions.

Environmental nanoplastics quantification by pyrolysis-gas chromatography–mass spectrometry in the Pearl River, China: First insights into spatiotemporal distributions, compositions, sources and risks

Nanoplastics (NPs, size <1000 nm) are ubiquitous plastic particles, potentially more abundant than microplastics in the environment; however, studies highlighting their distribution dynamics in freshwater are rare due to analytical limitations. Here, we investigated spatiotemporal levels of nine polymers of NPs in surface water samples (n = 30) from the full stretch of the Pearl River (sites, n = 15) using pyrolysis gas chromatography-mass spectrometry (Py-GC/MS). Six polymers were detected, including polystyrene (PS), polyvinyl chloride (PVC), nylon/polyamide 66 (PA66), polyester (PES), poly(methyl methacrylate) (PMMA) and polyethylene (PE), where three polymers showed high detection frequencies; PS (100 % in winter and summer), followed by PVC (73 % in winter and 87 % in summer) and PA66 (53 % in winter and 67 % in summer). The spatiotemporal distribution revealed the sites related to aquaculture (AQ) and shipping (SHP) showed higher NP levels than those of human settlement (HS) and wastewater treatment plants (WWTPs) (p = 0.004), and relatively high average levels of NPs in the urban sites compared to rural sites (p = 0.04), albeit showed no obvious seasonal differences (p = 0.78). For instance, the average PS levels in the Pearl River were in the following order: AQ 411.55 µg/L > SHP 81.75 µg/L > WWTP 56.66 µg/L > HS 47.75 µg/L in summer and HS 188.1 µg/L > SHP 103.55 µg/L > AQ 74.7 µg/L > WWTP 62.1 µg/L in winter. Source apportionment showed a higher contribution through domestic plastic waste emissions among urban sites, while rural sites showed an elevated contribution via aquaculture, agriculture, and surface run-off to the NP pollution. Risk assessment revealed that NPs at SHP and AQ sites posed a higher integrated risk in terms of pollution load index (PLI) than those at WWTP and HS sites. Regarding polymer hazard index (HI), 80 % of sampling sites in summer and 60 % of sampling sites in winter posed level III polymer risk, with PVC posing the highest risk. This study provides novel insights into the seasonal contamination and polymer risks of NP in the Pearl River, which will help to regulate the production and consumption of plastics in the region. Environmental ImplicationsThe contamination dynamics of field nanoplastics (NPs) in freshwater resources remain little understood, mainly attributed to analytical constraints. This study aims to highlight the spatiotemporal distribution of NPs in the Pearl River among various land use types, urban-rural comparison, seasonal comparison, their compositional profiles, potential sources, interaction with environmental factors, and ecological and polymer hazard assessments of investigated polymers in the full stretch of the Pearl River from Liuxi Reservoir to the Pearl River Delta (PRD) region. This study, with a comparatively large number of samples and NP polymers, will offer novel insights into the contamination profiles of nano-sized plastic particles in one of the important freshwater riverine systems in China.

Evaluation of enrofloxacin in the Chinese soft-shelled turtle (Pelodiscus sinensis) based on the biochemical, histopathological and intestinal microbiota responses

Enrofloxacin (ENR) is a veterinary medicine extensively used in aquatic farming, the abuses of antibacterials can lead to drug residues and toxicity to aquatic animals. Nevertheless, its toxicological effects on the Pelodiscus sinensis remain unclear. The objective of this work was to study the toxic effects of ENR on male P. sinensis following multiple oral administration. For hematological, antioxidant status, histological and ultrastructural analyzed, male P. sinensis were orally administrated with ENR for 5 consecutive days, each at the dose of 15 (recommended dose, 1×), 45 (3 times the recommended dose, 3×), and 75 (5 times the recommended dose, 5×) mg/kg body weight (BW) daily. The effect of ENR on P. sinensis by changes in the intestinal microbiota using high-throughput sequencing technology was also investigated. Samples of blood and fresh tissue (liver, spleen, intestine, muscle, spermary, testes, heart, lung, and kidney) were collected after 24 h of drug withdrawal. The results showed that multiple oral administration of ENR induced immunosuppression (lowered total proteins, alkaline phosphatase, and albumin), hepatic-renal dysfunction (elevated aspartate transaminase, alanine aminotransferase, urea nitrogen, K+ and Ca2+), and lowering the hepatic and splenic antioxidant functions (higher MDA, and declines in the activities of SOD, CAT, and NOS) in 3× ENR-dosed or 5× ENR-dosed groups. Noteworthy, histopathological and ultrastructural examination of tissue samples revealed adverse effects with increasing oral dosage of ENR. The 16S sequencing analysis showed that the ENR treatment can greatly change the intestinal microbial diversity and abundance in P. sinensis, but more probiotics such as Cetobacterium, Lactococcus, and Paraclostridium were retained in the short-term period. The findings may provide new insights into the toxicity of ENR to P. sinensis, and help to determine the dose to ensure the safety of aquatic food products.

A Study on Potential Feed Sources to Boost Guppy Fish, Poecilia reticulata Productivity

Aquaculture may simply be referred as “Underwater Agriculture.”India is a major maritime state and an important aquaculture- based country in the worldhaving major aquaculture activitiesin the production of Carp from Freshwater,Shrimp from Brackish water, etc. Feed requirements of fish vary in quantity and quality according to the feeding habits, physiological stages of the species and environmental variations viz., temperature; amount and type of natural food availability in the culture system.A nutritious and cheap feed is a pre requested for profitable aquaculture. Though, use of commercially available feed is in practice in many countries. The feed cost consumes more Than half of running expenditure. Therefore, the search of nutritionally well-balanced feed Prepared from very cheap locally available ingredients in progress in all the aqua farming countries. In the present study, an attempt has been made to well-balanced nutritious feed Particularly from the locally available cheaper ingredients. The objectives of the present study are: to assess the effect of feed on the growth of finfish and shellfish in the laboratory, to prepare the conventional feed with traditional ingredients and to check the effect of feed on the growth performance of ornamental fish - Guppy, Poecilia reticulata.

Development of Microcontroller Based Water Quality Monitoring and Water Level Control Device

Access to clean and safe water is not only a fundamental human right but also a vital requirement for electronics industries, chemicals industries, pharmaceuticals, food and beverage production, fisheries and aquatic farming. This project addresses the pressing issue of water quality monitoring and efficient water usage within the context of these industries. The study's identification of problem areas for water quality can lead to more efficient interventions and solutions to safeguard the environment, and prevent waterborne diseases. This paper presents the design and implementation of microcontroller-based system for monitoring water quality and water level in the thank, the water in the thank is refilled when it goes beyond a set threshold with the aid of an automatic switch control. The system is a hybrid of 3 subsystems: a Water Level Checker, a Water Quality Monitoring System and an Automatic Switch control system. The Water level checker consists of Ultrasonic sensors. The Water Quality Monitoring system consists of pH sensors, TDS (Total Dissolved Solids) sensors and Turbidity sensors. The continuous (Analog) data from the water quality sensors used would be outputted via an LCD (Liquid Crystal Display). The Automatic Switch control system consists of 5v Relay modules and a 12v Pump that would automatically switch ON/OFF depending on the level of water in the tank. The values of EC (Electrical Conductivity) and TDS spike drastically to the introduction of salt from as low as 138 -906 for TDS and 0.34 – 2.04 for EC, signifying increase in water capacity of electrical conductivity. Temperature rise in the afternoon also increases TDS values from 142 for clean water to 920 for the salty water while it ranges from 138 for clean water to 906 for salt water at both morning and evening time. Pumping aspects of the system are triggered when water level in the thank falls below 10% and trips off when water level goes above 95% as programmed in the control unit. The developed system marks a significant achievement in water management and automation technology. integration of quality monitoring sensors has enabled real-time evaluation of water parameters that holds potential for applications in environmental monitoring, ensuring safe drinking water, and safeguarding aquatic ecosystems. The automated switch control mechanism responds dynamically to water levels, enabling the system to trigger actions such as pump activation or filling processes based on predefined thresholds.

Analyzing the financial viability and technical efficiency of aquaculture farming in Delta State, Nigeria: Lessons from cluster operations

This study delved into the comprehensive analysis of aquaculture farming in Delta State, specifically focusing on the financial viability and technical efficiency of cluster operations. As aquaculture plays a crucial in meeting global seafood demands, understanding the dynamics at the regional level become imperative. The study employed a multifaceted approach to assess the financial viability of aquaculture farming, technical efficiency of aquaculture production. By adopting a cluster based perspective, the research aims to unravel the intricacies of collaborative farming operations, identifying synergies that contribute to enhanced financial outcome. Insights garnered from this financial evaluation can provide stakeholders with strategic guidance for sustainable economic practices within the aquaculture sector. The research draws on a diverse set of data source, including financial records, production metrics, focus group discussions and questionnaire distributions. Statistical tools and econometric models are applied to quantify the relationships between various variables, providing a clear understanding of the factors influencing technical efficiency and financial Findings from this study showed that the price of labour, price of fish feeds and price of medicine had a significant effect on efficiency of aqua farming with a coefficient of 0.5468**,-0.7862**, -0.8896** respectively. The result of the technical efficiency , (25.0%) falls within the 0.71 - 0.8 range, indicating a high level of technical efficiency of aqua farmers. This is followed by those in the 0.31 - 0.4 and 0.51 - 0.6 ranges, each with 11.2% of farmers. In contrast. The result of the BCR showed a significant variation in profitability highlights of aqua farming operations in the study area are more financially rewarding, with a net return on investment (ROI) of 0.58. However, the technical efficiencies and productivities of aqua farmers in clusters were significantly high regardless of how biases were corrected, implying that participation in cluster group is positively related to increases in aqua farmers output.

Briefing: Intensive inland aquaculture ponds: challenges and research opportunities

This briefing presents an overview of inland aquaculture scenario that focuses on challenges of aquaculture farming, contaminant transport and the future of aqua farming in a broader perspective of environmental geotechnics. Un-engineered aquaculture practices are a cause of concern, and special attention is necessary in waste water management, cross-contamination with the adjacent environment, sludge–subsoil interaction, pond embankment slope failure, leachate migration into the vadose zone, geoenvironmental remediation strategies and geotechnical engineering aspects of engineered pond construction.

Isolation, Identification, and Pathogenicity Characterization of a Largemouth Bass Ranavirus from Fujian, China

This study aimed to isolate and characterize the pathogenic agent of a suspected viral disease of largemouth bass (Micropeterus salmoides), which broke out in an aquatic farm in Fujian, China. The diseased bass had ulcer skin and muscles, bleeding fin, lesion liver, and enlarged spleen. Histopathological analysis showed multifocal necrosis on the gill, hepatopancreas spleen, and kidney. In the epithelioma papulosum cyprinid (EPC) cell line, stable cytopathic effects (CPE) were observed. Electron microscopy analysis showed icosahedral virus particles in the cytoplasm with a 150-160 nm diameter. PCR amplification revealed that the isolated virus belongs to largemouth bass ranavirus (LMBV) and was designated as LMBV FJ_22109. Further phylogenetic analysis determined that LMBV FJ_22109 is a variant of European and American strains. The intraperitoneal injection of LMBV FJ_22109 resulted in a regress infection, demonstrating its ability to induce pathogenicity in largemouth bass. The cumulative mortality rate was 100% at a culture temperature of 29°C, and 47% at a culture temperature of 17°C. Thus, it confirmed that LMBV FJ_22109 is indeed the causative agent of the suspected viral disease, and its virulence could be influenced by temperature, which will be beneficial for preventing and managing the disease.

Antibiotic resistance genes profile in the surface sediments of typical aquaculture areas across 15 major lakes in China

Aquatic farming is considered as a major source of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) for the natural environment of the lakes. ARB and ARGs in the natural environment have increased quickly because of the human activities. Here, we have profiled the diversity and abundance of ARGs in sediments from the typical aquaculture areas around 15 major lakes in China using PCR and qPCR, and further assessed the risk factor shaping the occurrence and distribution of ARGs. And class 1, 2 and 3 integrons were initially detected by PCR with specific primers. ARGs were widely distributed in the lakes: Weishan Lake and Poyang Lake showed high diversity of ARGs, followed by Dongting Lake, Chao Lake and Tai Lake. Generally, the ARGs in the Middle-Lower Yangtze Plain were more abundant than those in the Qinghai-Tibet Plateau. Tetracycline resistance genes (tet(C), tet(A) &tet(M)) were prominent in sediments, and the next was AmpC β-lactamase gene group BIL/LAT/CMY, and the last was the genes resistance to aminoglycoside (strA-strB). Partial least squares path modeling analysis (PLS-PMA) revealed that livestock had a significant direct effect on the distribution of ARGs in lakes, and population might indirectly influence the profiles of ARGs by affecting the scale of livestock and aquaculture. The detectable rate of class 1, 2 and 3 integrons were 80%, 100% and 46.67%, respectively. The prevalence of integrons might play a key role in promoting more frequent horizontal gene transfer (HGT) events, resulting in the environmental mobilization and dissemination of ARGs between bacteria.

Reproductive biology and feeding habit of Coilia dussumieri Valenciennes, 1848 (Actinopteri: Engraulidae): A review

Coilia dussumieri, regularly referred to as the goldspotted grenadier anchovy, is a ray-finned fish species that pertains to the Engraulidae family. Estuaries and maritime waters bordering Bangladesh, Myanmar, and India are home to it. On top of that, it can be found from Thailand south to Java and the Malay Peninsula. Any species' genetic features must be scrutinized in order to govern its population smoothly and figure out whether it is well-suited for culture. Fish biology encompasses a broad spectrum of disciplines, consisting of an in-depth overview of their stature, progression, gonado-somatic index (GSI), prime mating period, and fetal growth. Biology regarding consumption and procreation has been the focus of numerous research efforts in the recent past. The main goal of this review work is to bring together the disparate information, identify the knowledge gaps for additional research on this fish species, and provide aqua culturists with some information for future, more in-depth research on the culture, management, and breeding of Coilia dussumieri.

Biodegradability and bioavailability of dissolved substances in aquaculture effluent: Performance of indigenous bacteria, cyanobacteria, and green microalgae

Aquaculture is a controlled aquatic farming sector and one of the most important human food sources. Fish farming is one of the predominant, fast-growing sectors that supply seafood products worldwide. Along with its benefits, aquaculture practices can discharge large quantities of nutrients into the environment through non-treated or poorly treated wastewater. This study aims to understand the nutrient composition of fish wastewater and the use of indigenous bacteria, cyanobacteria, and microalgae as an alternative biological treatment method. Wastewater samples from a local fish farming facility were collected and treated using six different species of cyanobacteria and microalgae include Chroococcus minutus, Porphyridium cruentum, Chlorella vulgaris, Microcystis aeruginosa, Chlamydomonas reinhardtii, and Fischerella muscicola. All the samples were incubated for 21 days, and the following parameters were measured weekly: Chemical oxygen demand (COD), phosphate, total dissolved nitrogen, and dissolved inorganic nitrogen. In addition, dissolved organic nitrogen (DON), bioavailable DON (ABDON), and biodegradable DON (BDON) were calculated from the mass-balance equations. Colorimetric and digestive methods were used for the parameter measurements. The results showed that C. reinhardtii reduced the soluble COD concentration by 74.6 %, DON by 94.3 %, and phosphorous by more than 99 %. Moreover, M. aeruginosa, and C. minutus significantly reduced inorganic nitrogen species (>99 %). This alternative fish wastewater treatment method was explored to gain insight into fish wastewater nutrient composition and to create a sustainable alternative to conventional fish wastewater treatment methods.

Aquaculture the New Way of Creating Sustainable Livelihoods Among Rural Populations in Africa. A Case of Seke Rural District Zimbabwe

Aquaculture is one of the fastest growing agricultural activities in Zimbabwe in Zimbabwe today, a rare visit on social media you will be greeted by ads on aqua farming service providers. Thore aqua farming is broad in Asian communities where it is mainly practiced due to their strong fish diet especially in Easten Asia, prawns, fish and calamari to name a few are reared in Asia. In Africa the Nile tilapia is the most commonly reared fish in aqua culture. Food sustainability has been a key problem in Africa where most of the population live in rural setups where the rely on outdated farming methods and poor equipment which presents a challenge in production output. The main focus of this paper is to look on how aqua farming commonly known as fish farming has helped with sustainable livelihoods among rural populations with main focus being Seke in Zimbabwe. The research will look at the shortfalls that are faced by the farmers due to natural and man induced during the execution of the project. The recurring draughts in Zimbabwe in recent years has seen the need for an alternative sustainable livelihood to mainly horticulture-based economies like Seke District, aqua farming also helping in supplementing diet of the community as fish is highly nutritious and can be substituted for red meat which can easily be attacked by diseases. The research will show the role that has been played by aqua farming service providers in equipping the farmers with the know how to run the projects adequately, they have also been key to provide the materials that are necessary to carry out the projects. Job creation is also one area that the author will dwell on as aquaculture has made our rural areas better especially for the youth as they are the ones that are mainly responsible for the digging and construction of the ponds. This research will show the benefits and the shortfalls of aqua farming. The question will utilise interviews, data collection techniques and participant observation to support findings.

Sustainability in Aquaculture: A Note

Food production through aquaculture is one of the fastest-growing industries in the world. World aquaculture production is dominated by low-income food-deficit countries, which account for the majority of production. There is a great deal of expectation that aquaculture will contribute to the world's aquatic food production, and there is also hope that aquaculture will continue to grow in the future as a result of stagnant yields from many capture fisheries and increasing demand for fish and fishery products. In contrast, aquaculture is widely recognized as encompassing a wide range of different types of aquatic farming practices, such as seaweed farming, mollusk farming, crustacean farming, fish farming, and other aquatic species. Using different resource use patterns, there is a wide range of options for diversification, such as seaweed farming, mollusk farming, crustacean farming, and fish farming. Currently, aquaculture produces nearly a third of the world's edible fish supplies, and its contribution to marine food sources will only grow. As a sustainable alternative to catch fisheries, aquaculture has the potential to feed the world's rising population. Globally, aquaculture is the fastest-growing sector of the food industry, growing at a rate of more than 10% per year and accounting for more than 30% of all fish consumed. In regards to long-term sustainability, aquaculture faces the same issues as all other food production methods.

Integrated aquatic and terrestrial food production enhances micronutrient and economic productivity for nutrition-sensitive food systems

Integrated aquaculture–agriculture (IAA) is a form of crop diversification where aquatic and terrestrial foods are grown together on a single parcel of land. We compare economic and nutrient productivity per hectare for 12 distinct IAA combinations, identified from a representative survey of 721 farms in southern Bangladesh. Just under half of households integrate agriculture into their aquaculture production. Regression analyses show positive associations between the integration of terrestrial foods into aquatic farming systems and nutrient productivity, but that nutrient productivity is partly disconnected from economic productivity. However, we find that production of specific combinations of aquatic foods and vegetables can simultaneously improve nutrient productivity and economic productivity, thereby promoting nutrition-sensitive agriculture (NSA). The approach demonstrated here can be applied to the design of NSA programmes that are important for realizing nutrition-sensitive food systems.

The use of chemical and biological settlement cues in enhancing the larval settlement of abalone (Haliotis midae): Implications for hatcheries and ocean ranching

AbstractReducing the time to settlement and metamorphosis of abalone larvae is critical for ensuring that abalone larvae settle within the seeding site for ocean ranching or to increase production in hatcheries. This study investigated the effect of biological (planktonic Nitzschia sp.) and chemical (potassium chloride) cues in inducing settlement and metamorphosis of abalone larvae Haliotis midae on diatom‐coated plastic sheets. Larvae were exposed to different concentrations of KCl (10–20 mM), with settlement being highest at 10 mM in the first 20 h. Settlement of larvae exposed to a combined KCl and Nitzschia treatment for 24 h was highest, followed by larvae exposed to KCl for 12 h, while larvae exposed to KCl for 24 h, and both controls (12 and 24 h) had the lowest settlement. However, in both experiments, larval settlement in all treatments declined after 24 h of exposure, while that of the controls (no added settlement cues) increased and surpassed the other treatments after 24 h. Finally, the settlement was very low on uncoated sheets, compared to diatom‐coated sheets, regardless of exposure to different combinations of KCl and Nitzschia. The exposure period's results should be interpreted with caution when drawing biological conclusions for field studies. This is due to the dramatic decrease in mean settlement post‐exposure to the cue. Therefore, we hypothesize that exposure of H. midae larvae to 10 mM KCl and Nitzschia sp. will not enhance settlement in the ocean, as the inducers are primarily only effective at a KCl concentration level equal to 10 mM for 12 h. However, long‐term exposure to KCl and Nitzschia over 24 h could be used in hatcheries to improve the settlement of H. midae larvae.

Fructooligosaccharide and Bacillus subtilis synbiotic combination promoted disease resistance, but not growth performance, is additive in fish

Species diversification from major to minor carps for their sturdiness and initial higher growth, and also a quest for antibiotic-free aqua farming in the subcontinent, mandates search for and evaluation of alternatives. An experiment was performed to investigate the potential of fructooligosaccharide (FOS) and Bacillus subtilis (BS) (alone or as synbiotics) in promoting growth and immunity against infections in Labeo fimbriatus fingerlings. Six iso-nitrogenous and iso-lipidic diets containing combinations of two levels of FOS (0% and 0.5%) and three levels of BS (0, 104, 106 CFU/g feed) were fed to fish for 60 days. At the end of the feeding trial, twenty-four fish from each group were injected intra-peritoneally with pathogenic strain of Aeromonas hydrophila O:18 to test the immunoprotective efficacy of the supplements against bacterial infection. BS, but not FOS, significantly improved (P < 0.05) growth and feed utilisation attributes like percentage weight gain (PWG), specific growth rate (SGR) and feed conversion ratio (FCR). There were interactive effects of FOS and BS on PWG, SGR and FCR; however, the effects were not additive in nature. These beneficial effects of BS, alone or in combination with FOS, were corroborated by increased protease activity, microvilli density and diameter and number of goblet cells. Overall beneficial effects of FOS and BS included improved erythrocyte (RBC), hemoglobin (Hb), total protein and globulin levels. Total leucocyte (WBC) count and immunological parameters like respiratory burst activity of leucocytes (NBT reduction), lysozyme activity, albumin: globulin ratio and post-challenge survival were significantly improved by both FOS and BS, and their dietary combination yielded the highest improvement in these parameters. Synergistic effects of FOS and BS as dietary supplements indicate that a combination of 106 CFU/g BS and 0.5% FOS is optimal to improve growth, feed utilisation, immune functions, and disease resistance in L. fimbriatus fingerlings.

Prioritization of fish welfare issues in European salmonid aquaculture using the Delphi method

The European aquacultural sector is undergoing immense growth, and, generally, many more aquatic animals are farmed than land animals. However, the welfare of aquatic animals like fish has received less attention. This study focuses on the two largest contributors to Europe's aquaculture – Atlantic salmon and rainbow trout – farmed in cages in Northern Europe. An extensive literature review was conducted on potential welfare issues. These issues were grouped into five provisions / welfare aims according to an animal welfare framework adapted to fish. To set priorities among the issues, a Delphi assessment was performed, for which experts had to rate each issue based on the severity, duration, and prevalence. The participants were also asked to propose interventions to tackle the main issues. The three main welfare issues identified were ineffective prevention of diseases, sea lice treatment issues, and poor conditions during husbandry practices. Examples of interventions to improve the three main issues are lowering the stocking density, better monitoring, and specifically to prevent diseases, including sea lice, also developing more effective vaccines. This study provides valuable insights into which fish welfare issues should be tackled more urgently in European salmonid aquaculture. Future research could assess interventions more in depth and conduct similar studies for other aquatic farm animals and regions.

Genome Characterization and Infectivity Potential of Vibriophage-ϕLV6 with Lytic Activity against Luminescent Vibrios of Penaeus vannamei Shrimp Aquaculture.

Shrimp aquaculture, especially during the hatchery phase, is prone to economic losses due to infections caused by luminescent vibrios. In the wake of antimicrobial resistance (AMR) in bacteria and the food safety requirements of farmed shrimp, aqua culturists are seeking alternatives to antibiotics for shrimp health management, and bacteriophages are fast emerging as natural and bacteria-specific antimicrobial agents. This study analyzed the whole genome of vibriophage-ϕLV6 that showed lytic activity against six luminescent vibrios isolated from the larval tanks of P. vannamei shrimp hatcheries. The Vibriophage-ϕLV6 genome was 79,862 bp long with 48% G+C content and 107 ORFs that coded for 31 predicted protein functions, 75 hypothetical proteins, and a tRNA. Pertinently, the vibriophage-ϕLV6 genome harbored neither AMR determinants nor virulence genes, indicating its suitability for phage therapy. There is a paucity of whole genome-based information on vibriophages that lyse luminescent vibrios, and this study adds pertinent data to the database of V. harveyi infecting phage genomes and, to our knowledge, is the first vibriophage genome report from India. Transmission electron microscopy (TEM) of vibriophage-ϕLV6 revealed an icosahedral head (~73 nm) and a long, flexible tail (~191 nm) suggesting siphovirus morphology. The vibriophage-ϕLV6 phage at a multiplicity of infection (MOI) of 80 inhibited the growth of luminescent V. harveyi at 0.25%, 0.5%, 1%, 1.5%, 2%, 2.5%, and 3% salt gradients. In vivo experiments conducted with post-larvae of shrimp showed that vibriophage-ϕLV6 reduced luminescent vibrio counts and post-larval mortalities in the phage-treated tank compared to the bacteria-challenged tank, suggesting the potentiality of vibriophage-ϕLV6 as a promising candidate in treating luminescent vibriosis in shrimp aquaculture. The vibriophage-ϕLV6 survived for 30 days in salt (NaCl) concentrations ranging from 5 ppt to 50 ppt and was stable at 4 °C for 12 months.