Tank Experiments Research Articles

Effects of Salinity and Ca2+: Mg2+ Ratio on Growth Performance and Survival of Penaeus vannamei (Boone, 1931) Reared in Inland Saline Ground Water

Background: A 60-day experiment was conducted to evaluate the combined effect of salinity and Ca2+: Mg2+ ratio on the growth performance and survival of Penaeus vannamei reared in inland saline ground water (ISGW) at ICAR-Central Institute of Fisheries Education (CIFE), Rohtak Centre, Haryana, India. Methods: The study used three different salinities viz. T1 (5 ppt), T2 (10 ppt) and T3 (15 ppt) with four different level of Ca2+: Mg2+ rations such as 1:1, 1:2, 1:3 and 1:4. juveniles of P. vannamei with average body weight of 3.70±0.02 g, were stocked in 100 L capacity of circular plastic tanks. Total 36 experimental tanks were used as experimental unit. The stocking densities were 20 animals in each tank and each treatment were kept in triplicate followed the factorial design (3×4). Result: P. vannamei expressed better growth performance in terms of SGR, FCR, FER and PER in the T2 and T3 fortified Ca2+: Mg2+ ratio of 1:3. Lowest growth observed in T1 fortified with Ca2+: Mg2+ ratio 1:1. The study found 100% survival in T2 and T3 fortified with Ca2+: Mg2+ ratio of 1:3 compared with other treatment groups, which showed less than 80% survival. Based on the results, it can be concluded that the better growth performance, survival of P. vannamei observed in 10 and 15 ppt salinities of ISGW fortified with 1:3 ratio of Ca2+: Mg2+.

Environment Assessment of Modified Red Mud Utilized in Roadbed

Utilization of red mud in road projects is an effective way to consume large amounts of red mud on a large scale. In order to meet the requirements for road performance, a modified material, Heinchem, has been developed on the basis of extensive experiments, and the long-term environmental risks of red mud modified by this material have been investigated. By collecting and modifying original red mud samples, a series of continuous leaching tank experiments are carried out based on the exposure scenario analysis. According to the leaching content of pollution in the original and modified red mud, the characteristic pollutants are identified. The release mechanism of these characteristic pollutants in the modified red mud is revealed, and the long-term release amount is predicted. Furthermore, in light of the actual road use scenario of the modified red mud, a risk assessment model is established and used to simulate the release, migration, and transformation of characteristic pollutants during the use of modified red mud as roadbed material. The groundwater environmental risk is then assessed. Finally, an acute toxicity test of earthworms and a seed germination test are conducted to investigate the impact of the modified red mud on the farmlands. The results showed that the proposed red mud modified materials have obvious curing effects on V, As, Se, Mo, and F. When the leaching contents of V, Cr6+, Cr3+, As3+, Se4+, Se6+, Mo, and F in the modified red mud were lower than 0.15 mg/L, 0.1 mg/L, 0.2 mg/L, 0.012 mg/L, 0.012 mg/L, 0.012 mg/L, 0.075 mg/L, and 1.2 mg/L, respectively, the environmental risk of modified red mud during long-term road use is acceptable. This study provides a new way for the resource utilization of red mud.

Impact of Temperature on the Growth Performance, Survival Rate, Osmoregulation, Dissolved Oxygen and Physiological Changes of Freshwater Tilapia (Oreochromis mossambicus)

For many aquatic species, any changes in water temperature affect their survival. This study was performed to investigate the effect of rising temperature on the growth parameters, protein content, dissolved oxygen content, moisture content osmoregulation, and physiological activity of freshwater Tilapia (Oreochromis mossambicus). The experiments were set in plastic fish tanks, the experimental tank placed in direct sunlight and the control tank in shade, and measuring temperature and pH daily, with proper aeration and feed was provided. The study found that increasing water temperature led to higher mortality rates and low survivability percentages in fish, with a higher growth rate in the experimental group with a pH range of 5.7 to 8.2. High dissolved oxygen levels were recorded during the experimental period, with a mean difference of 26.56 compared to the control group, possibly causing restless movement in fish. The study revealed that the alkalinity of water decreases with increasing temperature. The study found that increased salinity led to a significant increase in growth performance, indicating an increase in metabolic rate, and a decrease in alkaline nature. The difference between the mean protein value in the experimental and control groups is 0.896mg/ml. Thermal limitations may negatively impact O. mossambicus physiological responses, impacting aquaculture production due to predicted global climate change-induced water temperature changes.

Short‐term survival and growth of American Eel elvers marked with visible implant elastomer tags

AbstractObjectiveVisible implant elastomer (VIE) tags are commonly used as a cost‐effective tool for marking small fish, making them valuable in mark–recapture studies. It is crucial to quantify the impact of tagging procedures on fish survival to address inferential bias in mark–recapture studies. We assessed marking‐related mortality and growth in American Eel Anguilla rostrata elvers in a 40‐day laboratory experiment, following VIE tag application.MethodsThere were 500 elvers (80–149 mm) that were divided into four treatment groups and one control group. Treatment groups were tagged with two tags in three body locations (anterior, central, posterior on left bilateral side) or with two tags in all three locations, while the control group remained untagged. Eels were retained in experimental tanks, and mortality rates were compared.ResultThe VIE tagging did not significantly affect survival, which was 90.9% across all treatment groups and 92% for the untagged control group; nor did it affect growth.ConclusionThe application of VIE tags on various body parts should be a safe and effective method for marking American Eel elvers.

First Feeding of Cuttlefish Hatchlings: Pioneering Attempts in Captive Breeding.

In the last few decades, the cuttlefish market has grown to approximately 14% of the world's fisheries, and operators have begun to express concerns about the decline of this resource. In this context, the production of cuttlefish through aquaculture could offer a diversifying and valuable response to the increasing market demand and help alleviate the environmental pressure on this species. Therefore, the aim of this study is to identify a dry, cost-effective, and easy-to-administer diet that can successfully support the initial phases of cuttlefish growth and provide a similar performance to a krill-based diet, which closely mimics their natural diet. To achieve this objective, cuttlefish hatchlings were distributed among different experimental tanks, each receiving one of the five different diets (namely Diets A to E). Mortality and morphological parameters were monitored until day 10 post hatching, and the two most effective diets (Diets A and B) were chosen for further trials. The results indicated that Diet B had similar survival and growth rates to Diet A, which was based on frozen krill. Histological analysis revealed a comparable degree of gut maturity between the organisms fed the two diets. Likewise, levels of amylase and trypsin enzymes and hsp70, cat, and sod mRNA did not exhibit significant differences between the two groups. In conclusion, our findings provide preliminary evidence supporting the possibility of cultivating cuttlefish in captivity using a pelleted diet, representing a promising starting point for larger-scale breeding efforts.

Electro-mechano transduction of stacked triboelectric nanogenerator considering wave force: Modeling, validation and applications

Aiming at the low-frequency characteristics of ocean wave energy, triboelectric nanogenerators (TENGs) provide an efficient collection method. We propose a multi-layer contact-separation mode triboelectric nanogenerator (MS-TENG) based on a frequency-up mechanism to collect water wave energy. First, we study the effects of frequency rising and TENG unit stacking on the output of the MS-TENG. Experiments show that the short-circuit current of the MS-TENG with 12 layers stacked is 152.16 μA when the rotating speed is 60 rpm. Compared with a single TENG unit, the short-circuit current of the MS-TENG is increased by 6.35 times. Second, the hydrodynamic simulation method is used to study the force and energy capture efficiency of floating bodies with different shapes in water waves. The results show that the energy capture efficiency of the cylindrical floating body is 70.14 % higher than that of the spherical floating body under the same volume. Third, we use a cylindrical floating body to package the MS-TENG. In water tank experiments, when the load resistance is 4 MΩ, the peak power density of the packaged MS-TENG is 14.56 W/m3. In addition, with the help of the MS-TENG, we set up a wireless temperature and humidity monitoring system to realize the preliminary marine environmental monitoring.

Effect of complexing agent on iron base zinc-nickel alloy coating

The influence of four complexing agents on corrosion resistance of Zinc-Nickel (Zn-Ni) alloy coating was investigated. The current density and plating time were determined by Hull and rectangular tank experiments. The effects of triethanolamine, potassium sodium tartrate, tetraethylenepentamine and sodium citrate on the properties of iron-based Zn-Ni alloy coatings were studied under the same electroplating process. The surface morphology, structure, elemental composition and corrosion resistance of Fe-base Zn-Ni alloy coatings with different complexing agents were analyzed. The surface and morphology of the coating were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The anticorrosive properties of the coating were evaluated by electrochemical electrode and electrochemical impedance spectroscopy (EIS). The self-corrosion current density of triethanolamine is 2.927e-005A·cm−2, the rate of corrosion is minimal, rendering the material highly resistant to corrosion; the surface remains flat and exhibits a dense texture. The content of potassium, sodium, Zn and Ni in tartrate increased, thus reducing the corrosion resistance and flatness of the coating. The self-corrosion current density was 9.400e-005A·cm−2. The surface was rough and uneven, and there were a large number of large concave and convex defects. The complexing agent enhances the adhesion and corrosion resistance of the coating, improves the optical and mechanical properties of the coating, adjusts the durability and stability of the coating, increases the crystal packing density, increases the coating thickness, improves the adhesion with the substrate interface, and optimizes the uniformity of grain distribution. These factors are the key factors that determine the corrosion behavior of Zn-Ni coatings. In the process of electroplating, the addition of complexing agent can improve the quality of the coating, and suitable complexing agent can obtain smooth and bright coating at the same time, make the corrosion resistance of the coating higher.

Ghost crab (Ocypode quadrata) modify their behavior during mirror exposure

Recently, ghost crabs (Ocypode quadrata) were shown to exhibit behavior consistent with passing the mark test, which implies the capacity for self-recognition. Considering this, it seems reasonable to suggest these animals can also distinguish their mirror image from different social stimuli, such as live conspecifics. In the current research, ghost crabs were placed in an experimental tank bisected by a mirror, clear partition separating a conspecific, and non-reflective partition on separate trials. Aggressive threat displays, time spent near partitions, eye cleaning, and partition contact were recorded during each condition. Results showed more aggression in trials with a conspecific present (i.e. clear partition), though this effect was only marginally significant. In addition, eye cleaning was significantly lower in the clear, compared to mirror and non-reflective treatments. Significantly more contact occurred with non-reflective partitions and time near each barrier was similar. These findings might suggest the capacity to distinguish mirror reflections from conspecifics, and mirror self-recognition could promote such ability. This, and other alternatives, are discussed as potential explanations for the observed effects.

Enhancement of Energy Harvesting PTO Against Nonlinear Waves Using Control System

Abstract Many systems include turbines, linear electromagnetic or hydroelectric components, as well as wave energy converters designed particularly for energy harvesting from ocean and sea waves. While each of these methods has its merits, it is also feasible to harvest a considerable quantity of energy generated by the sea and ocean waves. Wave energy is considered a renewable and ecologically friendly energy source. It is harvested through wave energy converters and is particularly useful to coastal nations. In this paper, a mechanical motion rectifier (MMR) is proposed to convert the bidirectional reciprocating movement of a floating body above the nonlinear wave into a rotating movement in one direction. Experimental investigations are carried out to examine the performance of the system. An experimental wave tank was built to produce nonlinear waves by controlled flapper motion. Mechanical and electrical efficiency were investigated for both systems. Through the use of a generator, the energy can be taken in the form of electrical energy and stored in appropriate batteries, resulting in clean and sustainable energy from the sea’s waves.

Flow patterns and heat transfer of an idealized square city in non-uniform heat flux and different background wind conditions

The city scale buoyancy-driven flow is crucial for the wind and thermal environment in urban areas, exerting a significant impact on the city ventilation, pollutants dispersion and heat removal. The intra-urban variations of hot spots and heat flux are drawing more attention on beating the urban heat. This study aims at analyzing the influences of non-uniform heat flux and background wind on the city-scale heat removal ability and underlying mechanisms. The large eddy simulation model was used and verified with water tank experiments. Results show that positive heat flux and negative heat flux in the rural areas will enhance and depress the strength of the urban heat dome flow respectively compared to the adiabatic condition. The high-speed regions are wider and stronger when the rural area has positive heat flux condition. Under positive rural heat flux condition, the time-average mixed layer height in urban areas across the city center plane is nearly twice that under negative rural heat flux condition. Besides, the city-scale heat transfer coefficients in positive rural heat flux condition are higher than those under negative rural heat flux and adiabatic conditions. For cases of non-uniform heat flux in urban areas, the differences of time-average mixed layer height and heat transfer coefficients are not obvious. The heat transfer coefficients decrease initially and then increase with increasing background wind speed indicating the non-linear interaction between approaching wind and urban heat dome flow. Moreover, the growth rate of the heat transfer coefficient decreases when the non-dimensional wind speed exceeds 1.19.

Research on Clustering-Based Fault Diagnosis during ROV Hovering Control

The objective of this study was to perform fault diagnosis (FD) specific to various faults that can occur in the thrusters of remotely operated vehicles (ROVs) during hovering control. Underwater thrusters are predominantly utilized as propulsion systems in the majority of ROVs and are essential components for implementing motions such as trajectory tracking and hovering. Faults in the underwater thrusters can limit the operational capabilities of ROVs, leading to permanent damage. Therefore, this study focused on the FD for faults frequently caused by external factors such as entanglement with floating debris and propeller breakage. For diagnosing faults, a data-based technique that identifies patterns according to data characteristics was utilized. In imitation of the fault situations, data for normal, breakage and entangled conditions were acquired, and Density-Based Spatial Clustering of Applications with Noise (DBSCAN) was employed to differentiate between these fault conditions. The proposed methodology was validated by configuring an ROV and conducting experiments in an engineering water tank to verify the performance of the FD.

Double-Swing Spring Origami Triboelectric Nanogenerators for Self-Powered Ocean Monitoring

Coastal areas often experience high population density and intense human activity owing to the considerable value of the ocean. Therefore, devices for monitoring marine disasters are crucial for ensuring the safety of human life. Herein, we develop hemispherical spring origami (SO) triboelectric nanogenerators (TENGs) (HSO-TENGs) for self-powered ocean wave monitoring. Optimization is performed using two approaches. First, swing machine experiments are conducted to investigate the monitoring performance of the HSO-TENGs regarding wave height and period with satisfactory accuracy. To increase power generation and monitoring accuracy, the internal inertia and centroid of gravity of the HSO-TENGs are optimized with respect to the structural parameters (i.e., magnet weight, hammer height, and external swing arm length). Second, numerical simulations are performed using the smoothed-particle hydrodynamics (SPH) method to determine the most suitable fixed condition for the HSO-TENGs for sensing wave changes. Subsequently, wave tank experiments are conducted on the HSO-TENGs to determine their ability to sense wave height, period, frequency, and direction. Tests related to supplying other sensors are also conducted. Eventually, the ability of the HSO-TENGs to monitor wave direction and spreading parameters is investigated in a numerical SPH circular wave tank. The results prove that the optimized HSO-TENGs can achieve powering and sensing through the same device.

Effect of fermented rice bran as a carbon source for rearing genetically improved farmed Tilapia, Oreochromis niloticus (Linnaeus, 1758), fry in biofloc system

Fermented rice bran, when used as a carbon source in a biofloc system, can improve water quality, growth, and feeding efficiencies of cultured species. The present study delves into the effect of fermented rice bran as a carbon source on the growth and survival of Genetically Improved Farmed Tilapia (GIFT) fry. Additionally, the study investigated its impact on water quality, intestinal histology, proximate composition of fish and biofloc, total plate count of the experimental tank, and fish gut in the biofloc system. The study employed a completely randomized design with five different treatments: NFRB+BFT (Non-Fermented Rice Bran), FRBW+BFT (Fermented Rice Bran with Water), FRBP+BFT (Fermented Rice Bran with Probiotic), FRBY+BFT (Fermented Rice Bran with Yeast), and a clear-water system (with daily water exchange of 10%). The experimental duration was 60 days. The GIFT fry with an average weight of 1.04 ± 0.02 g were randomly distributed in High Density Polythene (HDPE) tanks of 110 L capacity at a stocking density of 250 individuals (ind.) m−3. Results indicated that the weight gain %, length gain %, Specific Growth Rate (SGR), and Protein Efficiency Ratio (PER) in FRBP+BFT and FRBY+BFT treatments were similar, with no significant differences (p > 0.05) and significantly higher (p < 0.05) than other treatments. At the end of the experiment, FRBP+BFT and FRBY+BFT treatments showed lower ammonia-N values. The histological study of GIFT showed a number of villi and villi length in FRBP+BFT and FRBY+BFT were similar with no significant differences (p > 0.05). The protein, lipid, and ash content of fish and biofloc were similar with no significant differences (p > 0.05) in FRBP+BFT and FRBY+BFT treatments. The total plate count of fish gut and water in FRBP+BFT and FRBY+BFT treatments was similar and significantly higher (p < 0.05) than the other treatments. Overall, the results indicate that rice bran fermented with both probiotic and yeast as a carbon source showed similar growth performance and improved water quality in rearing GIFT fry in a biofloc system.

Multidimensional hybrid software-in-the-loop modeling approach for experimental analysis of a floating offshore wind turbine in wave tank experiments

A hybrid experimental modeling approach for floating offshore wind turbines (FOWTs) in a wave tank is presented. The method called real-time hybrid method (RTHM) or software-in-the-loop (SIL) includes physically reproduced hydrodynamic loads in the wave tank, with a Froude-scaled model while aerodynamic loads are reproduced on the model by an actuator. The force is applied on the tower top and calculated by a numerical simulation running in real-time as a function of the measured velocity and position of the physical model. Couplings between the platform motion, the aerodynamic loads and the wind turbine controller are hence accounted for. A new SIL actuator enabling the reproduction of a multi-component force at the tower top of an experimental scaled wind turbine model is developed, and the quantification of the accuracy of the replicated forces is studied. The test case includes a floating spar platform carrying a 10 MW horizontal axis wind turbine. The results show that this SIL actuator can accurately replicate the low and wave-frequency aerodynamic loads, which are essential for wave tank testing. Lastly, a case study of the wind turbine model in colinear and misaligned wind and wave conditions is presented, showing 3D forces and induced motions.

Effect of dietary protein reduction on growth performance and water quality of the blue streak hap Labidochromis caeruleus (Fryer, 1956) reared in a biofloc system

The 8-week study evaluated the effect of dietary protein reduction on growth performance and water quality of blue streak hap (Labidochromis caeruleus) using biofloc technology (BFT). Fish averaging 0.67 ± 0.13 g in weight were distributed into 15 polyester tanks, each with a water volume of 60 L within 100 L tanks, accommodating 15 fish per tank. Four isolipidic and isoenergetic diets were formulated with gradually decreasing protein levels (40%, 35%, 30%, and 25%). Four biofloc groups (40P + BF, 35P + BF, 30P + BF, and 25P + BF) and control (C) (40P + without BF) were fed twice daily (09:00 and 17:00) at a rate of 5% of their body weight. Molasses was added to the experimental tanks on a daily basis as an organic carbon source. This ensured that the biofloc tanks had a balanced carbon/nitrogen (C/N) ratio and facilitated control of total ammonia nitrogen (TAN), nitrite-nitrogen (NO2-N), and nitrate-nitrogen (NO3-N) levels. The nutritional composition of the bioflocs obtained from the experimental groups revealed that the crude protein and crude lipid contents were 37.00–38.14% and 1.45–1.52%, respectively (P > 0.05). The best specific growth rate (SGR) (1.68%) and feed conversation ratio (FCR) (2.21) were determined in the 35P group. Based on the overall evaluation of the study’s data, it can be concluded that the dietary protein for the blue streak hap (L. caeruleus) can be reduced from 40 to 35% in a biofloc system without any negative effects on health. Improving water quality and providing additional food to fish through zero water exchange and organic carbon addition (BFT) can be considered a sustainable aquaculture technique that can be used in ornamental fish farming.

Assessing eDNA capture method from aquatic environment to optimise recovery of human mt-eDNA

Previous studies have shown that environmental DNA (eDNA) from human sources can be recovered from natural bodies of water, and the generation of DNA profiles from such environmental samples may assist in forensic investigations. However, fundamental knowledge gaps exist around the factors influencing the probability of detecting human eDNA and the design of optimal sampling protocols. One of these is understanding the particle sizes eDNA signals are most strongly associated with and the most appropriate filter size needed for efficiently capturing eDNA particles. This study assessed the amount of mitochondrial eDNA associated with different particle sizes from human blood and skin cells recovered from freshwater samples. Samples (300 mL) were taken from experimental 10 L tanks of freshwater spiked with 50 µL of human blood or skin cells deposited by vigorously rubbing hands together for two minutes in freshwater. Subsamples were collected by passing 250 mL of experimental water sample through six different filter pore sizes (from 0.1 to 8 µm). This process was repeated at four time intervals after spiking over 72 hours to assess if the particle size of the amount of eDNA recovered changes as the eDNA degrades. Using a human-specific quantitative polymerase chain reaction (qPCR) assay targeting the HV1 mitochondrial gene region, the total amount of mitochondrial eDNA associated with different particle size fractions was determined. In the case of human blood, at 0 h, the 0.45 µm filter pore size captured the greatest amount of mitochondrial eDNA, capturing 42 % of the eDNA detected. The pattern then changed after 48 h, with the 5 µm filter pore size capturing the greatest amount of eDNA (67 %), and 81 % of eDNA at 72 h. Notably, a ten-fold dilution proved to be a valuable strategy for enhancing eDNA recovery from the 8 µm filter at all time points, primarily due to the PCR inhibition observed in hemoglobin. For human skin cells, the greatest amounts of eDNA were recovered from the 8 µm filter pore size and were consistent through time (capturing 37 %, 56 %, and 88 % of eDNA at 0 hours, 48 hours, and 72 hours respectively). There is a clear variation in the amount of eDNA recovered between different cell types, and in some forensic scenarios, there is likely to be a mix of cell types present. These results suggest it would be best to use a 5 µm filter pore size to capture human blood and an 8 µm filter pore size to capture human skin cells to maximize DNA recovery from freshwater samples. Depending on the cell type contributing to the eDNA, a combination of different filter pore sizes may be employed to optimize the recovery of human DNA from water samples. This study provides the groundwork for optimizing a strategy for the efficient recovery of human eDNA from aquatic environments, paving the way for its broader application in forensic and environmental sciences.

Smart nodding duck: A hybrid Halbach electromagnetic piezoelectric self-powered sensor for smart fisheries

Wave energy harvesting plays a crucial part in promoting the sustainable development of marine fisheries. This paper presents a novel hybrid electromagnetic and piezoelectric Self-powered Sensor, known as the Smart Nodding Duck (SND). The SND consists primarily of two components: an electromagnetic generator (EMG) responsible for power generation and a piezoelectric generator (PEG) dedicated to monitoring purposes. The SND absorbs wave energy through the shell of the nodding duck, while the planetary wheel system forms a coaxial counter-rotating augmentation structure. Also, the Halbach magnetic array serves as the electromagnetic generator, simultaneously exciting the piezoelectric structure to generate voltage signals. These features enable the SND to contribute to the LSTM network modeling self-sensing system, facilitating the monitoring of sea states. To verify the power generation effect of the SND, we conducted bench tests. The results demonstrate that the electromagnetic generator achieves an average output power of 96.26mW under a wave excitation of 0.8 Hz with an amplitude of 80 mm, yielding a power density of 16 W/m3. Furthermore, the self-sensing sea state monitoring model exhibits an impressive accuracy of 99.3 %. Moreover, tank experiment verified the feasibility of the SND, further contributing to the construction of a smart marine fishery Internet of Things.

Modelling and prediction of aeration efficiency of the venturi aeration system using ANN-PSO and ANN-GA

The significance of this study involves the optimisation of the aeration efficiency (AE) of the venturi aerator using an artificial neural network (ANN) technique integrated with an optimisation algorithm, i.e., particle swarm optimisation (PSO) and genetic algorithm (GA). To optimise the effects of operational factors on aeration efficiency by utilising a venturi aeration system, aeration experiments were conducted in an experimental tank with dimensions of 90cm×55cm×45cm. The operating parameters of the venturi aerator include throat length (TL), effective outlet pipe (EOP), and flow rate (Q) to estimate the efficacy of the venturi aerator in terms of AE. A 3–6-1 ANN model was developed and integrated with the PSO and GA techniques to find out the best possible optimal operating variables of the venturi aerator. The coefficient of determination (R2), root mean square error (RMSE), and mean absolute error (MAE) determined from the experimental and estimated data were used to assess and compare the performance of the ANN-PSO and ANN-GA modelling. It is shown that ANN-PSO provides a better result as compared to ANN-GA. The operational parameters, TL, EOP, and Q, were determined to have the most optimum values at 50 mm, 6 m, and 0.6 L/s, respectively. The optimised aeration efficiency of the venturi was found to be 0.105 kg O2/kWh at optimum operational circumstances. In fact, the neural network having an ideal design of (3-6-1) and a correlation coefficient value that is extremely close to unity has validated the results indicated above.

Trade-off between drag and catch performance when designing zooplankton trawls

The aquaculture sector is in pursuit of sustainable and cost-effective raw materials for feed, and the copepod Calanus finmarchicus is a marine zooplankton species of commercial interest because of its high abundance in northern areas. These copepods have the potential to meet the demand for vast quantities of marine raw materials. However, the lack of an energy- and catch-efficient trawl technology has limited the development of this fishery. Therefore, this study investigated the effect of two central trawl net design parameters mesh size and taper angle to identify which values that provide optimal trade-off balance between gear drag and catch efficiency. We conducted flume tank experiments using a series of plankton nets varying in mesh size (250–1000 μm), solidity ratio (0.54–0.76), and taper angle (5°– 30°) to acquire data on gear drag. The same nets were then used in fishing trials to obtain data on their catch performance. This study shows that zooplankton nets with a mesh size of approximately 500 μm and a low taper angle of about 5° provided the best trade-off between drag and catch performance.

Growth performance, health status and flesh quality of striped catfish (Pangasianodon hypophthalmus) reared in variable stocking densities in biofloc system

Optimization of ideal stocking density in intensive aquaculture system is a challenging appraisal. Higher stocking density is inducing chronic stress, impacting negatively on physiology and increasing disease associated risks in fish. Hence, the study was designed to evaluate the water quality, growth performance, health status and flesh quality of striped catfish (Pangasianodon hypophthalmus). The fish (2.61–2.64 ± 0.01 g initial body weight) were reared in randomly designed variable stocking densities (SDs) including five treatments (30, 40, 50, 60 and 70 fish m−3) in triplicates at C:N ratio 15:1 in jaggery supplemented biofloc system for 120 days in 1000 –L experimental fiber-reinforced plastic tanks. SD30 acted as control treatment having low stocking density. During the culture, pH, alkalinity and dissolved oxygen level decreased and BOD increased with increased stocking density. TDS and TSS level increased upto SD50 treatment and further decreased in higher stocking density treatments. Higher population of heterotrophic, ammonifying and nitrifying bacteria significantly (p < 0.05) reduced TAN, NH3-N, NO2-N, and elevated NO3-Nas well as rate and potential of ammonification and nitrification in SD50 treatment than other treatments. Bacillariophyceae and protozoa were most dominant group in the biofloc microbiome in all the treatments. Highly elevated biofloc volume, floc microbiome, good floc characteristics and floc quality might have enhanced fish survival rate, body weight gain, SGR through improving FCR in SD50 than other SDs. Moreover, higher population of gut microbiota (TPC and probiotic) and elevated digestive enzymes activity in fish reared in SD50 treatment significantly (p < 0.05) enhanced PER, ANPU, and somatic indices (GSI and HSI) as well as enhanced colour (lightness, yellowness/blueness and whiteness), flesh quality and hardness. Fish reared in SD50 treatment showed significantly (p < 0.05) higher haematological (TEC, TLC and Hb), immunological (TSP, albumin, RBA and lysozyme), antioxidant responses (higher SOD and CAT) and lower metabolic stress enzymes responses (ALT, AST and glucose). Moreover, fish reared in SD50 treatment showed improved villi surface area and height in intestine and slightly vacuolated hepatocytes in liver. Overall, significantly (p < 0.05) better water quality, fish performance, health status and flesh quality were observed in SD50. Collectively, the findings suggest that farmers can be benefitted by fetching higher production through suitable stocking density (50fish m−3) of P. hypophthalmus in biofloc with improved water quality, growth performance, health status and flesh quality.