Cage Aquaculture Research Articles

An application of maximum entropy model to evaluate the differential effect of cage aquaculture on the distribution of a native and an endemic fish species in Lake Maninjau, Indonesia

Physical cage aquaculture structure can attract native fish species in marine and freshwater ecosystems. Most studies on the effects of cage farms on native fish distribution have been undertaken in marine environments and outside of Asia as the main freshwater cage aquaculture producing region. Many studies have emphasised connections between native fish distribution and feeding time. Previous research also has shown the necessity to use modelling to monitor this effect to reduce data collection costs. Here we analyse the distribution of an endemic fish species, Rasbora maninjau, and a native fish, Gobiopterus sp., associated with tilapia cage aquaculture occurrence using a Maximum Entropy Model (MaxEnt). We find that the application of the MaxEnt model can produce reliable and accurate information on the impacts of cage aquaculture on the native fish species distribution aligning with the more expensive count data method. Our results also suggest that the species-specific interaction between the native fish and cage farms is mainly arising from an interaction between the ecological behaviour of the native fish with dimensions of the environmental condition such as turbidity. Our study therefore highlights the importance for improved appraisal of the ecology of native fish in the cage aquaculture risk assessment.

Features of parasitic diseases of salmonid fish in fishery reservoirs of the Leningrad region and Karelia

The probability of occurrence of parasitic diseases of salmonid fishes in modern fish-breeding enterprises of the Leningrad region and Karelia is very significant. Wild fish, in particular whitefish, are a reservoir of invasion, intermediate and final hosts for a number of parasites that are dangerous for rainbow trout. The purpose of this work is to study the characteristics of parasitic diseases of salmonids in fishery reservoirs of the Leningrad Region and Karelia. The studies of the parasite fauna of vendace were carried out in the period from 2019 to 2020. The examination of fish for the presence of parasites and their determination was carried out according to the generally accepted standard method. Of the helminthiases found in rainbow trout during artificial cultivation in the farms of the Leningrad Region and Karelia, monogeneans and cestodes present the greatest problem, and to a lesser extent, trematodes. In the fishery reservoirs of these regions, where cage aquaculture is actively developing, whitefish live, among which the European vendace or ripus (Coregonus albula) attracts special attention. In the study of the parasite fauna of vendace, 11 species of parasites from different systematic groups were noted. At the same time, gull tapeworm Diphyllobothrium dendriticum is of veterinary and medical importance. The parasites found in vendace can potentially be dangerous for cultivated salmonids, with special attention to the monogenetic fluke Discocotyle sagittata and the cestode D. dendriticum. These representatives of the ripus parasite fauna are also dangerous for rainbow trout. The control of the epizootic state makes it possible to detect infection and carry out a set of necessary therapeutic and preventive measures. Further study of the parasite fauna of wild whitefish in the lakes of the North-West of Russia is also important for the aquaculture of the region.

Effect of natural food consumption on the first phase of pirarucu grow-out in ponds and cages

ABSTRACT Pirarucu, Arapaima gigas is a fish species of great social and economic importance in the Amazon region, where they are often farmed in earthen ponds. Intensive cage aquaculture has been growing in Brazil, which could be an alternative means to farm pirarucu, reducing costs and increasing productivity. We evaluated the contribution of natural food organisms in semi-intensive (ponds) and intensive (cages) production systems, and their effect on pirarucu growth and economic performance during the first phase of grow-out. Four ponds (300 m2) and four cages (4.0 m³) were stocked, respectively, with 120 (0.4 fish m-²) and 160 (40 fish m-³) juvenile pirarucu (28.03 ± 6.34 g, 11.75 ± 0.80 cm). The study was conducted for 105 days and fish were fed with commercial feed. Fish growth and plankton intake were evaluated every two weeks. Survival rate, standard length, weight gain and final weight were higher in fish reared in earthen ponds than in cages. Feed conversion of fish kept in ponds was lower (0.96 ± 0.06) than in cages (1.20 ± 0.11). The consumption of natural food organisms was observed, despite artificial feed being fed in both systems. The relative abundance of zooplankton and insects in stomachs was directly proportional to fish weight gain in ponds, and inversely proportional in cages. Higher economic efficiency rate and lower average production cost were calculated for earthen ponds. Our results indicate that the cost-benefit of the first phase grow-out of A. gigas is better in earthen ponds.

Length-weight relationships and condition factors of mono- and mixed-sex Nile tilapia (Oreochromis niloticus) in open water cage culture system

The current study compared the length-weight relationships and condition factors in mono- and mixed-sex Nile tilapia (Oreochromis niloticus). The trial lasted for 91 days and included two treatments with five replications for each, all with the same stocking density. During the study period, 20 randomly selected fish individuals were measured and recorded from each cage every two weeks. The observed growth trend was allometric, with no significant difference in the mean exponential values (b), 2.696 and 2.65 for mono and mixed-sex tilapia respectively. There was a significant difference in final weight gain between monosex (171.58±7.39 g) and mixed-sex (149.09±4.14 g) tilapia. There was no significant difference in final length between monosex (19.80±0.42 cm) and mixed-sex (19.80±0.42 cm) tilapia. Moreover, the mean correlation coefficient (r2) of both groups was positive. The Fulton condition factor (K) also varies from 0.700 to 1.000 (monosex) and 1.000 to 1.010 (mixed-sex). The relative condition factor (Kn) for monosex and mixed-sex tilapia ranged from 1.96 to 2.222 and 2.092 to 2.35 respectively, indicated good aquaculture conditions. The present findings will attract fish farmers to mixed-sex tilapia culture by allowing them to lessen hormone administration and expected to boost national fish production through open water cage aquaculture.

Study of the Interaction between Regular Waves and a Wind-Fish Combined Structure

The combination of a wind turbine and fish cage (wind-fish) is able to solve the complex issue of power supply for deep-sea aquaculture. Nevertheless, the hydrodynamic coupling between the fish cage and the wind turbine foundation is increasingly complex, and there is little research on the related hydrodynamics. In this paper, the hydrodynamic research on the wind turbine foundation and fish cage structure is carried out using numerical simulation, in which the porous medium model is adopted to simulate the effects of the fish cage on the flow field. By analyzing the hydrodynamic characteristics of the combined structure of an offshore wind turbine and aquaculture cage under the action of regular waves, the load on both the cage in the combined structure and the wind turbine foundation, and the overall load on the combined structure of offshore wind turbine and cage are obtained. The effects of wave parameters, structural dimensions, cage submergence depth, and biological attachment on cage load, wind turbine foundation load, and overall load of the combined structure are analyzed. The results demonstrate that the wind turbine foundation is persistently the central part of the combined structure. The wave height, water depth, and degree of attachment of marine organisms all have different effects on the amplitude of the structural load. In contrast, the wave period, cage geometry, and cage submergence depth have no significant effects on the amplitude of the structural load. In addition to the water depth, other factors will affect the proportion of the load on the wind turbine foundation and the total load as well.

A new method to estimate the resistance coefficients of net panels modeled as porous media

Modeling net panels as thin porous media is an effective approach to carry out computational fluid dynamics (CFD) simulations of fishing nets and aquaculture cages. Existing methods to estimate the resistance coefficients for these porous media are based on simplified analytical models that relate these coefficients to the drag and lift coefficients of the panel. We propose a new method that uses a CFD model of the flow through a layer of porous media to estimate the resistance coefficients from regression analysis with experimental data. To increase the computational performance, the CFD model response is pre-calculated and interpolated in the regression analysis. The proposed method is applied to different net panels compared with existing methods. Results show that it provides better results than previous methods. Estimating both the inertial and the viscous resistance coefficients always provides better results than estimating just the inertial coefficients and it does not complicate the regression analysis with the proposed method. The method is easy to implement, fast and it could be used to estimate the resistance coefficients of materials other than net panels, since it does not make any assumption about the geometric characteristics of the actual material.

Analysis of hydraulic characteristics of fluid multiplier fish pump based on CFD simulation

The fish pump is an important power component for aquaculture, especially in offshore engineering vessel aquaculture and cage aquaculture. Reducing fish damage, improving survival rate, and increasing fish-lifting efficiency are the key points of fish pump research. In this study, we took a new type of fluid multiplier fish pump as the research object and selected many performance parameters that affect the hydrodynamic performance of the model prototype of the fish pump. The main conclusions are as follows: the fluid multiplier fish pump body produced a flow rate 2.8–3.5 times higher than the water injection port in the jet gap area, and under the influence of the high-flow-rate area, the low-pressure area generated at the fish inlet amplified the flow at the entrance of the fish. As a result, the fluid multiplier fish pump was able to suck and lift fish. With the change in the water jet gap from 2 mm to 4 mm, the head and flow of the bladeless fish pump were improved to a certain extent. We achieved an optimal value for the runner inclination angle during the change of the inclination angle of the pump body surface from −4° to 4°, and it reached the highest value when the inclination angle was 2°. In the process of increasing the water injection opening of the pump body from 50 mm to 65 mm, the head and flow of the bladeless fish pump greatly increased. The flow when the water injection opening was 65 mm was approximately 1.71 times that when the water injection opening was 50 mm. The head when the water injection opening was 65 mm was approximately 1.42 times that when the water injection opening was 50 mm. When the length of the guide vane was between 4 and 6 mm, the increase and decrease in the flow rate of the bladeless fish pump approached the maximum value of merit. The fluid multiplier fish pump designed in this study featured the characteristics of simple and lightweight structure and high fish-lifting flow, which can reduce labour intensity and improve the catching efficiency of aquaculture fish.

Semi-analytical study of wave interaction with a submerged permeable sphere applied on a spherical aquaculture cage

Spherical aquaculture cages are a technology of marine fish farming recently developed for installation in offshore areas. In harsh sea conditions, the cage can be temporarily fully immersed and safe from the intense loads. This paper studied semi-analytically linear waves incident to a submerged permeable sphere. The primary purpose of this research is to study the wave excitation forces, hydrodynamic coefficients, and wave strength inside the sphere. The problem's governing equations were established in the context of potential flow theory, considering two inner and outer regions and using multiple methods and Darcy's law for flow passing the porous media. The developed method was applied to the Aquapod spherical cage with a radius of a=9.0 m. The results indicate that the porosity parameter causes wave excitation forces and added mass decreases, but the damping coefficient increases significantly in the particular range of wavenumbers. Moreover, the peak value of the wave excitation force, damping coefficient, and the average of water particle velocities inside the cage occurs at ka=0.5, where k is the wavenumber. Also, at enough immersion, the damping coefficient is independent of depth. The results of this research are helpful in better understanding the behavior of spherical aquaculture cages in submergence conditions.

An Integrated Multi-Factor Coupling Approach for Marine Dynamic Disaster Assessment in China’s Coastal Waters

Marine dynamic disasters, such as storm surges and huge waves, can cause large economic and human losses. The assessment of marine dynamic disasters is, thus, important, but improvements to its reliability are needed. The current study improved and integrated the assessment from the perspective of multi-factor coupling. Using a weighted index system, a marine dynamic disaster assessment indicator system suitable for China’s coastal waters was established, and a method for calculating the weight of disaster indicators was proposed from the perspective of rapid assessment. To reduce the assessment deviation in coastal waters, a multi-factor coupling algorithm was proposed. This algorithm obtained amplitude variations of wave orbital motion in horizontal and vertical directions, which was used to evaluate the influence of background current and terrain slope on coastal ocean waves. Landsat 8 remote sensing images were used to carry out an object-oriented extraction of raft and cage aquaculture areas in China’s coastal waters. The aquaculture density was then used as the main basis for a vulnerability assessment. Finally, the whole assessment system was integrated and verified during a typical storm surge process in coastal waters around the Shandong Peninsula in China. The coupled variations were also added to the assessment process and increased the risk value by an average of 12% in the High Sea States of the case study.

Hydrodynamic Analysis of Rigid-Flexible Composite Structure of Large Aquaculture Platform Subjected to Waves

Deep-sea aquaculture cages have an important role in the marine fishery development process. With the increase of the sea depth, the sea conditions will be worse, as waves ups and downs, the stability performance of the cages decreases obviously. As the deep sea water is far away from the land, the environment is complex and changeable and the poor mobility of the system, all these factors can bring great economic losses to the aquaculture practitioners. Compared to the traditional cage system, the large aquaculture platform is more prominent. The aquaculture platform is composed of flexible bodies and slender rigid components. As the flexible bodies and the slender rigid components are coupled with each other, the response of the whole system is very complicated. For such a complex ocean system structure, the numerical simulation in the initial design stage can greatly speed up the design process and save many experimental resources. The aquaculture platform has been discretized into a lumped mass model based on the unique properties of a particular sea state and an aquaculture platform, and OrcaFlex has developed a dynamic simulation approach based on those parameters. With the change of the wave direction, the real-time response of the 6.8 thousand tons aquaculture platform under different wave directions has been realized. The dynamic response of the mooring system under different wave directions is obtained. The findings offer a theoretical foundation for the optimal aquaculture platform design.

UAV Path Planning and Obstacle Avoidance Based on Reinforcement Learning in 3D Environments

This study proposes using unmanned aerial vehicles (UAVs) to carry out tasks involving path planning and obstacle avoidance, and to explore how to improve work efficiency and ensure the flight safety of drones. One of the applications under consideration is aquaculture cage detection; the net-cages used in sea-farming are usually numerous and are scattered widely over the sea. It is necessary to save energy consumption so that the drones can complete all cage detections and return to their base on land. In recent years, the application of reinforcement learning has become more and more extensive. In this study, the proposed method is mainly based on the Q-learning algorithm to enable improvements to path planning, and we compare it with a well-known reinforcement learning state–action–reward–state–action (SARSA) algorithm. For the obstacle avoidance control procedure, the same reinforcement learning method is used for training in the AirSim virtual environment; the parameters are changed, and the training results are compared.

Nonlinear dynamics of an aquaculture cage array induced by wave-structure interactions

Computer simulations were conducted to understand the nonlinear dynamics of the cage array to establish an offshore fish farm capable of surviving the severe conditions. To that end, a large fish farm containing 16 net cages in a 2 × 8 configuration was modeled based on the lumped mass model. This numerical model was verified against the physical model tests regarding a single net cage and a net cage array. In particular, three different equivalent mesh groups were compared to each other to balance the numerical accuracy and the computational efficiency. Then, the candidate equivalent mesh group was used to separately model the rigid and the flexible cage arrays subjected to severe conditions. The results show that most trajectory patterns of mooring lines are not as elliptical as the water particle trajectories. This provides evidence to justify the perturbations about the equilibrium of the mooring grid for the full-scale aquaculture cage array system. Alongside this, flexible cages with lower bending stiffness have greater tension forces on the weather side. The bending stiffness has a predominant effect on the surge motion and is also the leading contributor to the nonlinearity of cage motion. The flexible cage with lower bending stiffness is appropriate for more exposed, open ocean fish farming applications, but the increased mooring tension should be taken into account for future design consideration.

Quantifying regional feed utilization, production and nutrient waste emission of Norwegian salmon cage aquaculture

We analyzed growth performance and waste emissions of cage aquaculture responding to biophysical conditions that vary along the coastline of Norway. The analysis is based on a published mass balance model predicting waste emissions and open quality-assured data from the Norwegian Directorate of Fisheries between 2016 and 2020. Results showed significant regional variation in feed conversion rate, with a steady increase from the Northern to Southern region (p < 0.001) and a co-occurring reduction in waste emission. The retention rate of feed carbon (C), nitrogen (N) and phosphorus (P) in tissues of farmed Atlantic salmon Salmo salar Linnaeus, 1758 varied from 39 to 43% of consumed nutrients across regions. The estimated defecation rate of C, N and P was 18% of consumption, whereas excretion or respiration varied from 39 to 43% across regions. This variability, along with farming methods and location characteristics, could potentially impact regional differences in benthic ecosystems. The regional differences in feed and environmental cost could potentially attract salmon farming to shift towards the Northern region, and this trend might become strengthened as water temperatures rise due to climate change. Additionally, salmon growth and feed intake rate interacted significantly with temperature (p < 0.001) and showed regular seasonal variation. The regulation of maximum allowed biomass restricts salmon farmers from increasing biomass beyond their maximum allowed level at any time. Nevertheless, the same biomass may cause higher waste in the summer. Therefore, we suggest an awareness of the seasonal increase in waste emissions and consideration of implementing environmental assessment for surface waters, which might be beneficial for decreasing the risk of reduced water quality.

Influence of net cages on water quality and trophic status of Lake Victoria, Kenya: The case of Kadimu Bay

AbstractWater quality is a critical component regulating ecosystem functioning in aquatic habitats, requiring regular monitoring for sustainable ecosystem services. Cage fish farming has the potential to affect water quality because of its rapid increase in many African waterbodies in response to dwindling wild fish stocks. Thus, there is a need for more studies to guide sustainable cage aquaculture in African lakes and reservoirs. This study evaluated the possible effects of cage farming of Nile tilapia (Oreochromis niloticus) on water quality parameters and the trophic state of Kadimu Bay, Lake Victoria, Kenya. Sampling for physicochemical and biological variables, including nutrient load, was conducted from January to October 2021, at five fish cage sites and a control site within the bay. In situ measurements of physical variables were undertaken in the field, while analysis of water samples for nutrient loads, biological and chemical variables was undertaken in the laboratory, following the methods described in APHA (American public health association standard methods for the examination of water and waste water. APHA‐AWWA‐WEF, 2005). The Carlson's Trophic State Index (CTSI) was used to classify the trophic state of the cage sites, while the total nitrogen:total phosphorus (TN:TP) ratio was used to determine the primary productivity limiting nutrient in the bay. The study results indicated electrical conductivity was significantly lower at the control (97.53 ± 4.17 μS/cm), compared to cage sites (105.42 ± 5.32 μS/cm at the Utonga cage site to 112.84 ± 1.94 μS/cm at the Oele cage site), indicating water of relatively lower quality at the cage sites. Similarly, the nitrite concentrations were higher at cage sites (6.35 ± .96 μg/L at the Uwaria cage site to 3.16 ± 2.25 μg/L at the Utonga cage site), and lower at the control site (2.68 ± 1.39 μg/L). In all, 14 physicochemical variables did not vary significantly between the cage and control sites, with nine variables (temperature, turbidity, electrical conductivity, total suspended solids, particulate organic matter, chlorophyll‐a, TP, nitrate and TN) being within the recommended thresholds for aquatic life processes. The bay was evaluated as being in a light eutrophic state, indicating moderate influence of the fish cages on the trophic state of the sites. There was a moderate relationship between chlorophyll‐a and TP concentration at the sampling sites (R2 = .50), compared to a stronger relationship with (R2 = .78). The TN:TP ratios were <10 at the sampling sites, indicating nitrogen was the limiting factor for primary production in the bay. The calculated CTSI suggests that the bay exhibited a light eutrophic state. Overall, although the results of this study showed cage aquaculture is not a current challenge to the water quality of the bay, regular monitoring is nevertheless recommended to inform sustainable aquaculture development in the bay and lake.

Effect of Smoking and Grilling on Polycyclic Aromatic Hydrocarbons in Ghanaian Tilapia.

The study assessed 18 Polycyclic Aromatic Hydrocarbons (PAHs) in O. niloticus (Nile tilapia) sampled from an aquaculture cage (farm) and a wild catch. The PAHs in fish samples were analysed using Gas Chromatography-Mass Spectrometry. Four PAHs (in order of levels: Indeno [1,2,3-cd] pyrene > Anthracene > Perylene > Pyrene; 100-0.8 µg/kg) and only one PAH (Pyrene: 4 µg/kg) were detected in raw samples from the cage and wild catch respectively. Chargrilling significantly increased Pyrene levels after cooking (wild: 4-11 µg/kg; cage: 5-23 µg/kg, p < .05), and likewise Anthracene levels in cage samples (13-153 µg/kg) but decreased Indeno [1,2,3-cd] pyrene levels from 100 ± 20 to 1.2 ± 0.2 µg/kg in cage samples. Smoking significantly increased 13 to 15 PAH congeners' levels (from < 1.0 up to 340 µg/kg) and total PAHs (wild: 4 to 840 µg/kg; cage: 110 to 560 µg/kg), and decreased Indeno [1,2,3-cd] pyrene (100 to 1.3 µg/kg) in cage samples but showed no effect on Benzo [g, h, i] perylene and Dibenzo [a, h] anthracene levels in all samples. For smoked samples, Benzo [a] pyrene and PAH4 (Benzo [a] anthracene, Chrysene, Benzo [b] fluoranthene, and Benzo [a] pyrene) exceeded the respective maximum permissible limits of 2 µg/kg and 12 µg/kg, and significantly influenced the levels of carcinogenic PAHs (CPAH, 135-170 µg/kg). Nevertheless, the Excess Cancer Risk (ECR) estimates, from a conservative approach, were far below the threshold (10-4), implying that consuming smoked or grilled tilapia from the study site is safe.

Effect of sea cage aquaculture on the length, weight, and condition of wild Atlantic cod Gadus morhua

Wild fish have been shown to associate with sea cage aquaculture and consume waste feed; however, little is known about the effects of waste feed consumption on wild fish. We used Atlantic cod Gadus morhua collected in the direct vicinity of sea cages and reference Northwest Atlantic Fisheries Organization divisions, either outside the direct vicinity (‘local division’) or completely removed from aquaculture (‘outside divisions’), to compare length, weight, and condition for cod ages 2 to 4. Concentrations of vegetable oil-based fatty acids (linoleic acid and α-linolenic acid) were then used as biomarkers for waste feed consumption to determine their role in explaining differences in length, weight, and Fulton’s condition index among cage-associated cod. Age 2 cage-associated cod were in lower condition than age 2 cod from the local division and lighter than age 2 cod from all outside divisions. Age 3 cage-associated cod were comparable to age 3 cod from the local division but in lower condition than age 3 cod from all outside divisions. However, age 4 cage-associated cod were longer and heavier than age 4 cod from the local division, but in lower condition than age 4 cod from 2 of 3 outside divisions. Additionally, there were positive relationships between fatty acid concentrations and length and weight for age 2 cage-associated cod, but no significant relationships for age 3 or 4 cage-associated cod. Results suggest the effects of waste feed consumption are contradictory but not consistent enough to disrupt established growth and condition patterns among divisions.

Fish health knowledge, management practices and prophylactic health products usage in aquaculture systems in Kenya

ABSTRACT This study assessed knowledge in fish health, management practices and usage of prophylactic health products (PHPs) in pond and cage aquaculture systems in Kenya. Data were collected using semi-structured questionnaires in 220 fish farms randomly selected from six counties, which were previously recorded to be producing high quantities of cultured fish in the country. Prophylactic health products used for fish health management in the farms surveyed were mainly water and soil treatment compounds, disinfectants, antibiotics, and probiotics. Among the farmers surveyed, only 11.9% of the pond fish farms sought advice on fish health issues from specialists compared to 59.3% in the cage culture systems. Thirty-seven percent of cage culture farmers were aware of probiotics and their benefits compared to 5.7% of the pond farmers. The study concluded that knowledge of fish health management practices by fish farmers is still inadequate and there is a need to train fish farmers and fisheries staff to build their capacity on fish health and management.

Vitality as a measure of animal welfare during purse seine pumping related crowding of Atlantic mackerel (Scomber scrombrus)

The impacts of wild capture fishing on animal welfare are poorly understood. During purse seine fishing for Atlantic mackerel (Scomber scrombrus), catches are crowded to high densities to facilitate pumping onboard. This study aimed to monitor fish welfare during crowding events in the Norwegian purse seine fishery, and to identify relevant drivers. We first correlated a suite of neuro-endocrine, physiological and physical stress responses (integrated into a single measure of welfare using multivariate analysis) to the behavioural vitality of individual mackerel in controlled crowding trials in aquaculture cages. Vitality was found to be a useful measure of welfare. We then assessed individual fish vitality onboard a commercial purse seiner. Catch welfare, measured using vitality, was observed to be negatively impacted during pumping related crowding. Larger catches and longer crowding exposure times resulted in greater negative impacts. Vitality was not significantly impacted by crowding density or dissolved oxygen concentrations inside the net, although methodological limitations limited accurate measurement of these parameters. Blood lactate levels correlated negatively with vitality, suggesting that high-intensity anaerobic locomotory activity was associated with the reduction in welfare. Based on these findings, catch welfare could be improved by targeting smaller schools to minimise crowding exposure times.

Bottlenose dolphins share fish farm areas while maintaining sexual segregation: Investigating group memberships through spatially and temporally explicit parameters

Abstract Group membership is a key attribute of animal societies and central to the study of social structure in several taxa. However, social structure analyses are sensitive to the way data are collected and associations defined. In this study, a time–space method was used to investigate the social structure of common bottlenose dolphins Tursiops truncatus observed and photographed across 7 years in the semi‐enclosed Gulf of Corinth, Greece. Instead of adopting traditional group definitions, individuals were considered as being members of the same group if photographed within a specific time and space window. This approach can be applied post hoc across studies and can offer advantages under challenging sampling conditions (e.g. when dealing with groups spread over vast areas or when group membership is otherwise hard to assess). Dolphins were mostly found around coastal cage aquaculture facilities farming European sea bass Dicentrarchus labrax and gilthead seabream Sparus aurata. Dolphins formed clusters largely or entirely composed of individuals of the same sex, suggestive of sex‐based homophily. Habitat partitioning was not detected: there was substantial spatial overlap among dolphin clusters, with all individuals using a relatively small area in the northern portion of the Gulf, where most of the productive fish farms were located. Associations between females were stronger than those between males, and daughters tended to stay in the group of their mothers. Sex‐based social clustering may allow females and calves to limit interactions with potentially aggressive males, while individuals of both sexes benefit from prey concentrated around fish farms. Adaptation to foraging around farms can result in trade‐offs between the costs and benefits of nourishment and social interaction. This may have both positive or negative effects on the animals that should be considered in the context of ensuring their favourable conservation status.

The variation of intestinal autochthonous bacteria in cultured tiger pufferfish Takifugu rubripes.

Intestinal autochthonous bacteria play important roles in the maintenance of the physiological homeostasis of animals, especially contributing to the host immune system. In the present study, the variation of autochthonous bacterial community in the intestinal tract of 2-7 months-old tiger pufferfish Takifugu rubripes and bacterial communities in the seawater of recirculating aquaculture system (RAS) and the following offshore sea cage aquaculture system (OSCS) were analyzed during the aquaculture period from May to October 2021. Proteobacteria was found to be the most dominant phyla in both intestinal and seawater bacterial communities, which accounted for 68.82% and 65.65% of the total bacterial abundance, respectively. Arcobacter was the most core bacterial taxon in the intestinal bacterial community, with the most dominant abundance (42.89%) at the genus level and dominant positions in co-occurrence relationships with other bacterial taxa (node-betweenness value of 150). Enterococcaceae was specifically enriched in the intestinal bacterial community of pufferfishes from RAS, while Vibrionaceae was enriched in the intestinal bacterial community from OSCS. The F-values of beta diversity analysis between intestinal and seawater bacterial communities generally increased from May (6.69) to October (32.32), indicating the increasing differences between the intestinal and seawater bacterial communities along with the aquaculture process. Four bacterial taxa of Weissella sp., Akkermansia muciniphila, Dietzia sp. and Psychrobacter pacificensis had significant correlations with immune response parameters, and they were suggested to be the indicators for immune status and pathological process of pufferfish. The knowledge about the specific core bacteria, potentially pathogenic bacteria and the change of bacterial community in the intestinal tract of cultured pufferfish is of great scientific significance and will contribute to the understanding of intestinal bacterial homeostasis and biosecurity practice in pufferfish aquaculture.