Fish Size Research Articles

Movement traits important to conservation and fisheries management: an example with red snapper

Site fidelity, space use, and dispersal are commonly estimated with acoustic telemetry (AT) to help inform management and conservation. These behaviors can change with age, habitat and environmental conditions and our ability to accurately estimate them is affected by a study’s inference power (design components that affect how accurately detection data represents a species’ movements). Red snapper (Lutjanus campechanus) have been extensively studied with AT over a range of time periods and regions, although primarily at artificial reefs (AR). Here, we use large (> 12 km2) acoustic positioning arrays to monitor a study area with low-relief hard bottom, a reef ledge, and an AR. Annual fidelity to the study area was estimated to be 54%, but estimates were affected by fate uncertainty and model choice. Emigration increased with storms and in early summer. Abundance was greatest at small habitat patches but space use did not scale with patch size. Although uncommon, long-distance movements and connectivity between habitats occurred, with a maximum dispersal of 206 km. Previous red snapper AT studies varied greatly in array size, study duration, and number of fish tracked, impacting inference power. This made it difficult to compare results and highlights the need for greater standardization in AT methods.

Identification of Critical and Tolerable Fish Habitat Requirements Based on Pre- and Post-Typhoon Data

Catastrophic typhoons with heavy rainfall introduce massive flow and fine sediments into stream channels. In addition, the natural disturbances and engineering practices afterward may strongly alter the fish abundance and their environment. This study compared physical habitat parameters and fish abundance before and after two major typhoons using two sampling period datasets (November 2008–March 2009 and May 2011–March 2012). The study area was in the Cishan Stream, a tributary of the Gaoping River in southern Taiwan. This area experienced two strong typhoons (Morakot and Fanapi) between the two sampling periods, providing an opportunity to compare pre- and post-typhoon conditions. The collected species were Hemimyzon formosanus, Rhinogobius nantaiensis, Onychostoma alticorpus, Candidia barbata, Acrossocheilus paradoxus, and Spinibarbus hollandi. Our results show a decrease in substrate size, fish size, and fish weight after typhoons. The river channel transformed into an unstable condition after the heavy rains, as major habitat types in our sampling stations changed from riffles with coarse substrate to runs with fine substrate. The results of statistical tests indicate the different habitat requirements of three major fish species (H. formosanus, R. nantaiensis, and O. alticorpus) and can indicate whether species’ requirements change between the two sampling periods. Water depth and pebbles were critical habitat requirements for the adults of H. formosanus; water depth, pebbles, and sand were critical habitat requirements for the adults of R. nantaiensis; and flow velocity and standard deviation of flow velocity were critical requirements for the juveniles of O. alticorpus. Understanding habitat requirements can provide useful information for post-disaster restoration and contribute to eco-sensitive river engineering.

The Atlantic salmon gill transcriptional response to natural infection with HPR0-ISAV (Isavirus salaris) in three Norwegian smolt farms.

Infectious Salmon Anaemia virus (ISAV) is an orthomyxovirus that causes large economic losses in Atlantic salmon (Salmo salar L.) aquaculture. All virulent ISAV variants originally emerged from a non-virulent subtype, ISAV-HPR0. Transient ISAV-HPR0 infections are common in both freshwater and marine environments. ISAV-HPR0 infects juveniles, marine salmon at on-growing sites, and broodstock salmon. The shift in virulence from ISAV-HPR0 to the virulent HPRΔ is suggested to be a stochastic event that depends on the virus's replication frequency. Therefore, reducing the capacity to maintain ISAV-HPR0 infection within individual farms may limit the risk of emerging pathogenic ISAV variants and ISA disease. The absence of infection-related clinical signs and the lack of experimental models limit our understanding of ISAV-HPR0-host interactions. We characterise the host transcriptional response to natural ISAV-HPR0 infection, using Atlantic salmon gill tissues collected on three Norwegian smolt farms. The comparison of all infected (qPCR-positive) and non-infected (qPCR-negative) individuals revealed a classic antiviral response in the gills of ISAV-HPR0 infected fish in a site-independent transcriptomic analysis. Complementary analyses showed that the response to infection varied considerably between sites. Site-specific differences could be associated with a range of factors that are challenging to control in field studies, such as fish size, the stage of infection, and the presence of additional microorganisms. Our findings enhance our understanding of how Atlantic salmon respond to ISAV-HPR0 infection, pinpointing common HPR0-induced antiviral response genes. Future studies should investigate whether these candidate genes limit virus replication in the gill for risk of novel transitions to virulence.

A Novel Power-operated Fish Cutting Machine: Design and Performance Assessment

Fish, a critical source of protein, plays a vital role in global food security. Fish processing involves descaling, gutting, deheading, and cutting. Traditionally small vendors and retailers manually cut the fish steaks using Sharp metal knives. However, manual cutting methods are inefficient, labor-intensive, and pose safety risks. This study presents a novel power-operated fish-cutting machine design, development, and performance evaluation to address these limitations. The machine incorporates a mainframe, cutting blade, roller system, feeding section, and power transmission mechanism. Its performance was assessed using various fish species (Catla, Silver sillago, Flying Fish) by analyzing the influence of cutting blade speed, feeding angle, and distance between the cutting blades on cutting efficiency, cutting time, and damage. The results demonstrated that all three factors significantly impacted the cutting process. By optimizing these parameters, the machine achieved a maximum efficiency of 98.59% with a cutting rate of 0.5 minutes per kilogram of fish at a roller speed of 1200 rpm, a feeding angle of 120 degrees, and a distance between the cutting blades of 40 mm for silver sillago. Furthermore, the study revealed that fish variety, size, length, and distance between the cutting blades significantly influence the machine's performance, highlighting the need for potential adjustments based on specific fish characteristics.

Influences of gonad developmental stage on ovary selenium concentrations in fish-implications for ovary selenium monitoring.

Monitoring selenium (Se) concentrations in fish ovaries is an important tool for evaluating the ecological risk posed by Se in aquatic systems. Most guidance recommends sampling fish ovaries as closely as possible to when fish spawn on the premise that Se is mobilized from the liver to the ovary during vitellogenesis, and therefore, sampling ovaries during the early phases of oocyte maturation may underestimate egg Se concentrations at the time of spawning. In this study, we evaluated ovary Se data from two species with synchronous oocyte development (Ptychocheilus oregonensis and Prosopium williamsoni), one species with asynchronous oocyte development (Richardsonius balteatus), and one where the mode of development is unclear (Mylocheilus caurinus). A multivariate analysis of ovary Se as a function of fish sampling location, size, and gonado-somatic index (GSI) demonstrated ovary Se was strongly negatively correlated with GSI in fish species with synchronous oocyte development but only weakly correlated in a species with asynchronous development. In R. balteatus, a relationship between expressible (released) egg Se and remaining ovary Se was observed, with egg concentrations ∼54% of ovary concentrations on average. Overall, our findings suggest that current understanding of the mechanisms by which Se is maternally transferred to oocytes is not entirely correct and raises questions regarding how and when during the reproductive cycle Se is mobilized to ovaries. Further, our findings have significant implications for interpretation of ovary Se monitoring data collected from unripe fish. We developed regression-based models to correct ovary Se data that are biased by sampling females not in spawning condition and demonstrate how this bias can impact evaluation of Se risk to fish.

Assessment of the physiological state of the Caspian beluga juveniles before release into their natural habitat

The results of the study of juvenile beluga before release into the natural habitat in the Volga-Caspian fishery basin in 2024 are presented in this paper. The relevance of the work lies in the need to obtain information about the physiological state of released juveniles, which is necessary to understand the possibility of fish adaptation to natural conditions. Growing conditions and fish-biological parameters of juvenile fish were studied and analysed. The size and weight parameters of fish and Fulton fatness are determined. Hydrochemical parameters during the period of beluga juvenile rearing were within the limits of values recommended for sturgeon rearing in pools of closed water exchange installations (CWE). As a result of statistical analysis of survival rate, size and weight indices of juveniles reared in 2024, it can be concluded that the fish breeding material was homogeneous and corresponded to the average long-term results obtained when rearing juveniles at the scientific and experimental complex of aquaculture “BIOS” under industrial conditions. The physiological condition of 10 g beluga juveniles reared in the conditions of UZV basins was assessed during the research. Lifetime blood sampling from the tail vein was carried out in order to study some physiological and biochemical parameters: hemoglobin, total serum protein, albumin, cholesterol, triglycerides, glucose, phosphorus. The results of the studies were statistically analysed and the variability of physiological and biochemical blood parameters in juvenile beluga whales was calculated. Beluga juveniles for research were obtained from the breeding stock included in the “Unique scientific installation” of the Russian Federal Research Institute of Fisheries and Oceanography “Bioresource collection of aquatic biological Resources”, released into a reservoir of fishery significance without pathologies, in satisfactory condition.

Effect of hydrolyzed red worm (Eisenia foétida) on production parameters in red tilapia (Oreochromis sp.)

Background Conventional fish feed based on fish meal, meat, and soy cake presents procurement difficulties and high costs, affecting the profitability and sustainability of the aquaculture industry. Objective To evaluate the effect of hydrolyzed red worm (HRW- Eisenia foétida) in red tilapia (Oreochromis sp.) diet on production parameters. Methods The study was conducted at the aquaculture farm of the Politécnico Colombiano Jaime Isaza Cadavid (PCJIC) at 780 m.a.s.l.,with an average temperature of 28 °C. Ninety red tilapia fingerlings, averaging 7,5±0,5 g, were distributed in nine aquariums containing 75 liters of water. Fish underwentweight and size measurements at the beginning and end of the trial. They were fed experimental diets to apparent satiation three times daily. Water quality parameters and productive rates of growth and nutrient utilization were measured. The experimental design included three treatments with three replicates each: T1 (control diet, 0% hydrolysate inclusion), T2 (10% hydrolysate inclusion), and T3 (20% hydrolysate inclusion). ANOVA (p<0,05) was applied to growth and nutrient utilization variables, with mean comparisons using α<0,05 in SPSS version 25. Results Significant differences (p<0,04) were found between the control diet T1 (0% inclusion) and T2 (10% inclusion) in favor of weight gain (31,87 g). There were no statistical differences in size increase (p<0,217). As HRWinclusion increased, feed consumption decreased, likely due to higher hydrolyzed protein availability. Feed conversion rates showed significant differences (p<0,001) between T2 and T3 compared to T1, indicating better assimilation of the hydrolyzed protein. T2 and T3 also showed better protein and energy efficiency (p<0,001), demonstrating the hydrolyzed protein’s nutritional quality and assimilation. Diet cost decreased with higher hydrolyzed inclusion (p<0,034). Conclusion Inclusion 10% and 20% hydrolyzed red worms significantly improved production parameters and reduced costs, making it a viable alternative for feeding red tilapia for small and medium-scale producers.

The size and weight composition of by-catches of sturgeon fish by stationary seines in the near-shore area of the southeastern sector of the Sea of Azov

The aim: the characteristics of the species, size and weight composition of sturgeon fish in the near-shore zone of the Sea of Azov.Material: bycatch data from scientific monitoring of So-iuy mullet fisheries with stationary seines in the waters of the Temryuk Bay and in the Kerch Strait near the Chushka Spit in April 2024.Results: sturgeon species were encountered in stationary seines in 100% of cases. The average catch per seine was 2–11 specimens per day. Starry sturgeon in Temryuk Bay accounted for more than 40% of the sturgeon bycatch, but it was not encountered in the Kerch Strait. Beluga Huso huso was noted in the Kerch Strait. The size range of Russian sturgeon varied from 30 cm to 133 cm; Starry sturgeon — from 102 to 118 cm. The average size of Russian sturgeon was 92.1 and 99.8 cm with an average weight of 9.2 and 6.4 kg, respectively, near the Chushka Spit and at the mouth of the Kuban. The average size of Starry sturgeon was 110.1 cm with an average weight of 6.7 kg. The length of the Beluga was 73 and 190 cm. The share of Russian sturgeon of commercial size (>90 cm) near Chushka Spit was 55%, in Temryuk Bay — 79%. 100% individuals of Starry sturgeon at the mouth of the Kuban were of commercially acceptable size (>80 cm).Practical value: Observations of bycatch in stationary seines in the near-shore zone are the important source of data on the qualitative characteristics of sturgeon populations in the Sea of Azov.

Ulcerative dermal necrosis of mature Atlantic salmon in the Kola and Tuloma rivers (Murmansk region): retrospective and prospects for studying the problem

The aim of the work is to analyze the results of virological and immunological studies, to track the dynamics of the entry and changes in external signs of pathology of Atlantic salmon into the Kola and Tuloma rivers.Methods used: fish size and weight indicators were determined using generally accepted methods. Methods for isolating viruses on continuous cell lines and their identification in RT-PCR reaction were used. Bactericidal activity of blood serum (BABS) was assessed using a nephelometric method. The content of non-specific immune complexes (IC) was established using a spectrophotometric method with selective precipitation with PEG-6000.According to the results of the work, it was revealed that in the Kola and Tuloma rivers, clinical manifestations of pathologies in fish have changed. Since 2021, typical symptoms of UDN have been replaced by signs of «red skin disease». The results of immunological studies indicate high activity of innate humoral immunity mechanisms in the examined individuals. The carriage of infectious pancreatic necrosis virus in Atlantic salmon populations living in the Kola and Tuloma rivers has been established. Clinical signs of pathology in Atlantic salmon are described in detail, and fish counting data for the Kola and Tuloma rivers are presented.The novelty of the work: for the first time, photographs of all noted typical signs of pathology, as well as the results of virological and immunological studies of Atlantic salmon in the Kola and Tuloma rivers for 2022–2024 are presented. A retrospective overview is given and prospects for studying the problem are outlined.Practical significance: the conducted research will allow creating a database on the results of comprehensive studies of Atlantic salmon diseases in the Kola and Tuloma rivers. Compare the results obtained in fish with and without clinical signs of pathologies over several years. Determine differences in the immune status of fish with different signs of pathology based on the results of long-term studies. This will help to understand how UDN disease develops over time and what causes it.

Individual movement behaviour and habitat use of a small-sized cypriniform (Telestes muticellus) in a mountain stream

Knowledge about the biology and ecology of species is fundamental for their management and conservation. Despite this, many fish species and life stages are understudied, and there is a great need for research efforts to understand their ecology. Italian riffle dace (Telestes muticellus; order Cypriniformes) is a small-sized (< 15 cm) stream fish native to the Italian peninsula. There is a scarcity of research on its ecology and behaviour. In this study, we explored the movement ecology of Telestes muticellus in a Mediterranean mountain stream in Northern Italy using passive integrated transponder (PIT) telemetry. Over 15 months, 267 fish were located 2–27 times. Most fish remained stationary, while a few roamed over several hundreds of meters. Fish covered a larger linear range during spring and autumn than during other seasons. T. muticellus showed a strong preference for pools, and this preference was strongest during summer. We observed no differences in habitat use and movements between day and night, and fish size had no major effect. Within pools, many T. muticellus displayed remarkably small home ranges (median 8 m2). Fish increased their linear ranges over a period of flood events, indicating that high-flow events may be important for the downstream and upstream dispersal of T. muticellus in small mountain streams.

Variation in the population structure of bluegill bully (Gobiomorphus hubbsi) with distance upriver: implications for river connectivity

ABSTRACT The bluegill bully is a small (TL < 100 mm) eleotrid fish that inhabits fast flowing habitats in New Zealand rivers. Bluegill bullies are amphidromous with larvae developing at sea and juveniles migrating upriver to adult rearing habitats in freshwaters. Throughout New Zealand, more than 90% of adults occur within 50 km upstream of river mouths. This species, therefore, has a relatively restricted longitudinal distribution in rivers compared with most other amphidromous fish species in New Zealand. In the Motu River, females were smaller than males (mean TL of 62 mm versus 72 mm). The mean length of both sexes increased with distance upriver, and although females dominated the population (77% of all fish), the proportion of males increased with distance upriver. Consequently, population structure in terms of both fish size and sex ratio varied with distance upriver. Due to the spatial variation in population structure, the loss of riverine connectivity resulting from anthropogenic obstructions may reduce habitat for the larger fish, especially the largest males. It may also alter population structure, thereby influencing selective pressures contributing to population fitness and further impacting populations of this vulnerable native fish.

Species-specific mercury speciation in billfishes and its implications for food safety monitoring and dietary advice.

Humans are exposed to toxic methylmercury mainly by consuming marine fish, in particular top predator species like billfishes or tunas. In seafood risk assessments, mercury is assumed to be mostly present as organic methylmercury in predatory fishes; yet high percentages of inorganic mercury were recently reported in marlins, suggesting markedly different methylmercury metabolism across species. We quantified total mercury and methylmercury concentrations in muscle of four billfish species from the Indian and the Pacific oceans to address this knowledge gap. We found low percentages of methylmercury in blue and black marlins (15±7%) compared to swordfish and striped marlin (89±13%), with no significant differences among ocean regions. This illustrates that billfishes exhibit species-specific methylmercury bioaccumulation patterns, likely related to unique selenium-dependent in vivo methylmercury demethylation capacities in muscle. Blue and black marlins therefore appeared generally safer for human consumption than swordfish and striped marlin regarding MeHg toxicological effects. Yet, no matter the species, the frequency of recommended weekly billfish meals decreased with increasing fish size, given that mercury naturally accumulates over time. When assessing potential risks of billfish consumption, we therefore recommend measuring methylmercury, rather than total mercury, and relying on a large number of samples to cover a broad range of fish sizes. This study calls for additional characterization of mercury speciation and bioavailability in billfishes to better understand the mechanisms driving species-specific differences of methylmercury detoxification, and to refine dietary advices associated to marine top predators consumption.

First report of Patagonian toothfish (Dissostichus eleginoides) metabolic rate and its scaling on a surface culture system.

Dissostichus eleginoides is a benthopelagic, carnivorous fish from circumpolar antarctic waters. It is a deep sea fish distributed up to 2500 m and reaching up to 200 kg, 2 m total length and over 50 years of lifespan. Although it is of commercial interest, with prices between 14-35 US$/kg, studies that allow its cultivation are scarce. D. eleginoides is considered to have a slow metabolism since it lives at low temperatures (2-11 °C) and high pressures (100-250 atmospheres). However, there are no records of their routine aerobic metabolism (or any in fact) and of their mass scaling in tanks captivity on the surface, being the aims of this study. Routine metabolism was measured in fish groups from 3 sizes, a) 2.31 ± 0.08 kg, b) 4.67 ± 0.06 kg and c) 8.97 ± 1.89 kg in two respirometry chambers allowing to perform closed respirometry. The average metabolic rate was 42.91 ± 0.48, 38.61 ± 2.64 and 35.35 ± 1.58 mg O2 kg-1 h-1 along fish sizes, with significant differences between sizes. The calculated scaling exponent was 0.85, similar to that reported for other cold-water fish species measured at the surface. Results show oxygen consumption rates, under surface pressure conditions, comparable to those of G. morhua and salmonids, which allows, preliminarily, to reject the initial hypothesis of a slow metabolism. Although the results are preliminary, they are the first to report on the routine metabolism of this species, making them relevant for future studies. Culture densities of 87.38, 57.77 and 64.92 kg m-3 were estimated for groups a, b and c presenting important advantages and new perspectives for the cultivation of D. eleginoides.

Evaluation of the primary production and maximum fish production in Salman Farsi Reservoir, Fars Province, Iran

Primary production in water bodies corresponds to their fish production capacity. Aquaculture planning for water resources is conducted based on specific geographical conditions and their internal and external factors. Understanding the fish production capacity of lakes enables predictions for exploitation (fishing) and restoration of reserves. This research aims to estimate the primary production of the Salman Farsi Reservoir, Fars Province, on the Ghare Aghaj River, to evaluate fish production capacity and plan aquaculture development. Sampling was conducted to measure dissolved oxygen, water temperature, pH, conductivity, transparency, total phosphorus, total nitrogen, and chlorophyll-a in three transversal sections along the side, surface, and deep areas of the open water, with three repetitions in four seasons during 2023 – 2024. Trophic conditions were estimated using Trophic Status Index (TSI) models. Total production of the lake was calculated using the Brämick-Lemke and Koeschel models, while fish production was calculated using the Brämick-Lemke and Downing models. The annual average of dissolved oxygen, transparency, electrical conductivity, pH, total phosphorus, total nitrogen, and chlorophyll-a concentration in the lake was 8.2 ppm, 4.1 meters, 1387 μS/cm, 8.3, 0.174 ppm, 4.50 ppm, and 1.38 ppm, respectively. The average TSI based on transparency, phosphorus, chlorophyll-a, and Carlson’s index was 40, 78, 33, and 50. The initial production size in the lake was estimated 292 gC.m-²y-1. Fish production capacity was calculated based on primary production at 39 Kg.ha-1.y-1 and based on phosphorus at 33 Kg.ha-1.y-1, with an average of 36 Kg.ha-1.y-1. Considering the 2000-hectare livable area for fish in the lake, the total fish production this year was estimated at 71.8 tons. Under current lake conditions, the allowable fishing size was estimated to be 7 to 11 tons of fish per year. Determining the production capacity and trophic level can help maximize exploitation while minimizing ecological impacts and potential risks associated with restocking and fishing, such as the introduction of excessive juvenile fish into the lake.

Biology of One of the Most Abundant Mesopelagic Fish in Icelandic and Surrounding Waters: The Krøyer's Lantern Fish Notoscopelus kroyeri (Malm, 1861)

ABSTRACTMyctophids play an essential role in the marine ecosystem, linking the surface to the mesopelagic layer through diel vertical migration, and contributing to carbon sequestration. However, basic knowledge of their biology and distribution is still limited. Here, we described the length and age distribution, growth and otolith morphometrics for one of the most abundant myctophid fish of the Northeast Atlantic, the Krøyer's lantern fish Notoscopelus kroyeri (Malm, 1861). Individuals were sampled opportunistically by pelagic trawls during the International Ecosystem Summer Survey in the Nordic Seas (IESSNS) conducted in July 2020 and 2021. We provide the length–weight and otolith–fish size relationships and the size distribution for 336 N. kroyeri individuals collected along Iceland's south and west shelf, the Iceland Basin, and the Irminger Sea. Fish were primarily distributed along the Reykjanes Ridge and the continental shelf at depths between 0 and 550 m. Three size groups, corresponding to three different age groups, with individuals from 2 to 9 years old, were detected across sampling areas. We found positive allometric growth during both sampling years. Linear regressions were significant between otolith length, width and area, and fish length and weight, with adjusted r2 values ranging between 0.93 and 0.94. This study provides new information on the biology and distribution of one of the most abundant mesopelagic species in south Icelandic and surrounding waters.

Recreational Anglers’ Specialization and Perception of Management Measures in Yucatan, Mexico

ABSTRACT Understanding anglers’ diversity can help to improve the effectiveness of governing recreational fisheries. Online and in situ surveys were applied to evaluate perceptions and preferences among anglers’ fishing frequency (occasional, regular, and frequent) as an indicator of their specialization in Yucatan, Mexico. Occasional anglers’ most reported fish species are associated with bottom fishing (non-selective), while regular and frequent with trolling and casting (selective). The primary fate of the catches was to preserve the sizes they considered large enough and release the small ones. Unlike occasional, the frequent does not consider overexploited species to be affected by this fishery. The fish size regulation was chosen as the most effective management measure among anglers of all specialization levels. The social and ecological context of the Yucatecan coast must be considered before introducing management measures, and resource managers must establish collaboration strategies with the most specialized anglers to promote best fishing practices.

Erçek Gölü’nde farklı ağ göz genişliğine sahip multifilament fanyalı uzatma ağlarının seçiciliği

This study was conducted in Lake Erçek, located in the Van Lake basin. The study examined the selectivity of multifilament trammel nets used in the fishing of pearl mullet (Alburnus tarichi, Güldenstädt, 1814) in the lake. The efficiency of nets with mesh sizes of 22 mm, 24 mm, and 26 mm was evaluated in the research. A total of 5.336 pearl mullets were caught in the study carried out between October 2021 and April 2022. 1.296, 1.721 and 2.319 fish were caught from nets with mesh sizes of 22. 24 and 26 mm, respectively. The aim of the study was to determine the most suitable mesh size for sustainable pearl mullet fishing in Lake Erçek. The Holt (1963) method was used to calculate the selectivity parameters. This method considers the fish length and mesh size to determine which size of fish can be caught by the nets. The calculations showed that nets with a 26 mm mesh size had the highest efficiency and contributed to the preservation of fish stocks by allowing smaller fish to escape. The optimum catch lengths for the 22 mm, 24 mm, and 26 mm nets were calculated as 21.15 cm, 22.47 cm, and 23.69 cm, respectively. It was particularly noted that nets with a 22 mm mesh size caught fish below the legal catch size, which could negatively affect the sustainability of the fish stocks. As a result, it was concluded that nets with a 26 mm mesh size are the most suitable option for sustainable fishing in Lake Erçek. The findings of the study provide important data for the conservation of pearl mullet stocks and for the sustainable management of fishing practices.

Economic Analysis of Red Tilapia (Oreochromis sp.) Production Under Different Solar Energy Alternatives in a Commercial Biofloc System in Colombia

The study investigates the economic aspects of red tilapia (Oreochromis sp.) production using biofloc technology under different electrical energy sources. Conducted at the El Vergel Fish Farming Association in Arauca, Colombia, the study examines four energy treatments: conventional energy (CE), combined conventional and photovoltaic energy (CPVE), full photovoltaic energy (PVE), and simulation of photovoltaic energy generating surplus for nighttime use (PVES). The water quality and zootechnical performance met the species requirements, with dissolved oxygen decreasing as fish size increased. The PVE treatment had the highest initial investment due to solar panels and battery costs, but it also had the lowest operating energy costs. However, the overall costs of the PVE treatment increased due to depreciation and maintenance. Feed was the largest production cost, followed by labor in most treatments, while depreciation was a major cost for the PVE treatment. The total operating cost (TOC) of the photovoltaic energy systems (PVE and PVES) was lower compared to that of conventional energy (CE), with PVES showing the highest cost savings. The reduction in energy costs highlights the potential for solar energy systems to enhance the economic viability of aquaculture production, making these systems a favorable option for sustainable production in the long term.

Managing the Dissolved Oxygen Balance of Open Atlantic Salmon Sea Cages: A Narrative Review

ABSTRACTAs Atlantic salmon depend on dissolved oxygen (DO) to survive and grow, managing DO is essential for welfare and growth. However, the dynamics of DO in the open sea cages are complex, caused by a range of factors that interact and create compounding effects. To understand DO dynamics, two pillars of knowledge are essential: the supply of DO to the cages and the consumption of DO in the cages. The components of these two pillars vary greatly across both time and space, with factors including ambient sea temperature and current, density stratification, fish size, health and metabolism, biomass density and distribution, topography, production routines and farm configuration. In the production environment, these factors often interact, making related analyses on effects, causality and effective management highly challenging. Exacerbating matters, existing knowledge is fragmented across multiple disciplines, making it challenging for end‐users to access. Using sensors is often necessary to understand and manage the complexity of DO, and the interest to implement digital technologies to aquaculture operations and utilize big data analyses is growing, but to succeed in the application, an in‐depth understanding of the relevant dynamics is necessary. Consequently, this review is produced to compile existing knowledge on the many factors that influence the consumption or supply of DO in the sea cages, and their relationship to each other. In this narrative review, we explore the known interactions and compounding effects between these factors, and synthesize it in a causal diagram for holistic analyses of the DO balance.

Environmental and Spatial Effects on Co‐Occurrence Network Size and Taxonomic Similarity in Stream Diatoms, Insects and Fish

ABSTRACTAimThe influences of environmental and spatial processes on species composition have been at the center of metacommunity ecology. Conversely, the relative importance of these processes for species co‐occurrences and taxonomic similarity has remained poorly understood. We hypothesised that at a subcontinental scale, shared environmental preference would be the major driver of co‐occurrences across species groups. In contrast, co‐occurrences due to shared dispersal history were more likely in dispersal‐limited taxa. Finally, we tested whether taxa co‐occurring due to similar responses to environmental and spatial processes were more taxonomically similar than expected by chance.LocationThe conterminous United States.Time Period1993–2019.Major Taxa StudiedStream diatoms, insects and fish.MethodsWe generated co‐occurrence networks and developed methodology to determine the proportions of nodes and edges explained by pure environment alone (after accounting for space), pure space alone (after accounting for the environment), pure environment and pure space together, and spatially structured environment. Taxonomic similarity of taxa co‐occurring because of environmental and/or spatial controls or because of unmeasured processes was compared to that of a null model.ResultsPure environment alone, spatially structured environment, and pure environment and pure space together explained the greatest proportion of nodes and edges in the co‐occurrence networks of diatom species and genera, and insect genera. Conversely, pure environment and pure space together best explained the nodes and edges in the co‐occurrence network of fish species and genera. Co‐occurring taxa were more closely related than the random expectation in all comparisons.Main ConclusionsThe environment controlled co‐occurrences in all groups, while the influence of space was the strongest in fish, the most dispersal‐limited group in our study. All co‐occurring taxa were more taxonomically related than expected by chance due to environmental or spatial overlap or unaccounted factors.