Individual Fish Research Articles

Robust Fish Recognition Using Foundation Models toward Automatic Fish Resource Management

Resource management for fisheries plays a pivotal role in fostering a sustainable fisheries industry. In Japan, resource surveys rely on manual measurements by staff, incurring high costs and limitations on the number of feasible measurements. This study endeavors to revolutionize resource surveys by implementing image-recognition technology. Our methodology involves developing a system that detects individual fish regions in images and automatically identifies crucial keypoints for accurate fish length measurements. We use grounded-segment-anything (Grounded-SAM), a foundation model for fish instance segmentation. Additionally, we employ a Mask Keypoint R-CNN trained on the fish image bank (FIB), which is an original dataset of fish images, to accurately detect significant fish keypoints. Diverse fish images were gathered for evaluation experiments, demonstrating the robust capabilities of the proposed method in accurately detecting both fish regions and keypoints.

A fish appetite assessment method based on improved ByteTrack and spatiotemporal graph convolutional network

The appetite of fish significantly influences aquaculture efficiency and fish welfare. However, accurately assessing fish appetite has posed a challenging problem. Currently, the study of fish feeding behaviour relies primarily on the overall information obtained from images of fish schools, often overlooking the distinctive behavioural traits of individual fish. Analysing the behaviour of individual fish is hindered by challenges such as intraclass variation and cross-occlusion within real aquaculture environments. To address these challenges, this paper introduces a novel method for assessing appetite based on individual fish behaviour. The ByteTrack model was improved to enable stable tracking of each fish within a school under complex conditions. Additionally, this paper employs the spatiotemporal graph convolutional neural network (ST-GCN) to extract the movement characteristics of individual fish, facilitating accurate appetite assessment. The experimental results demonstrate that the proposed method achieves 98.47% accuracy in appetite assessment, surpassing the performance of other state-of-the-art methods. This paper provides a new opportunity and effective means for analysing fish behaviour and appetite in intricate environments.

Space partitioning within groups of social coral reef fish

Site-attached fish that form social groups may face a trade-off between the advantages of group living and the disadvantages related to intra-group competition for food. A possible solution for the latter is space partitioning among group members. Technological limitations related to individual tagging and underwater tracking hindered such spatial studies in grouping fishes. Here, using underwater video cameras and recent developments in deep learning tools, we successfully tracked the 3D movements of individually tagged fish in 4 groups of the damselfish Dascyllus marginatus in the coral reef of Eilat, Red Sea. Our findings, based on tracking sessions lasting 3–11 min that were recorded during a period of > 1 month, show that the individual fish kept separate foraging spaces with minimal overlap and that this separation was stable in time. When the tidally driven current reversed, the separation was kept, and a corresponding reversal was found in the positions of each fish relative to the coral and its neighbors. We propose that the stable spatial partitioning observed in our study is a primary mechanism through which site-attached species can organize themselves in order to reduce intra-group competition.

Assessment of the impact of microplastic ingestion in striped red mullets from an Eastern Mediterranean coastal area (Zakynthos Island, Ionian Sea)

Monitoring microplastics (MPs) in the marine environment is an ongoing process, and our understanding of their impact on marine organisms is limited. The present study evaluates the effects of ingested MPs on the marine MP pollution bioindicator fish species Mullus surmuletus. The study follows a three-fold approach to assess the impact of MPs on marine organisms by investigating: 1) the ingestion of MPs, 2) the bioaccumulation of phthalate compounds as plastic additives, and 3) the evaluation of toxicological biochemical and cellular biomarkers. Striped red mullets were sampled in the marine protected area (MPA) of the National Marine Park of Zakynthos and coastal sites with high touristic pressure in Zakynthos Island in the Ionian Sea, Greece. Fewer ingested MPs and lower phthalate concentrations were found in fish inside the MPA compared to those sampled outside the marine park. However, no relationship was found between either phthalate concentrations or biomarker levels with the ingested MPs in the red striped mullets. Biomarker levels were influenced by season and site, but no effect could be attributed to the ingested MPs. The lack of association of biomarker responses and plasticizer bioaccumulation to MP ingestion can be explained by the low number of ingested MPs in the fish from Zakynthos coastal area as MP abundance ranged from 0.15 to 0.55 items per individual fish.

Divergent responses of pelagic and benthic fish body-size structure to remoteness and protection from humans.

Animal body-size variation influences multiple processes in marine ecosystems, but habitat heterogeneity has prevented a comprehensive assessment of size across pelagic (midwater) and benthic (seabed) systems along anthropic gradients. In this work, we derive fish size indicators from 17,411 stereo baited-video deployments to test for differences between pelagic and benthic responses to remoteness from human pressures and effectiveness of marine protected areas (MPAs). From records of 823,849 individual fish, we report divergent responses between systems, with pelagic size structure more profoundly eroded near human markets than benthic size structure, signifying greater vulnerability of pelagic systems to human pressure. Effective protection of benthic size structure can be achieved through MPAs placed near markets, thereby contributing to benthic habitat restoration and the recovery of associated fishes. By contrast, recovery of the world's largest and most endangered fishes in pelagic systems requires the creation of highly protected areas in remote locations, including on the High Seas, where protection efforts lag.

Temperature‐Dependence Assumptions Drive Projected Responses of Diverse Size‐Based Food Webs to Warming

AbstractFood web projections are critical for evaluating potential risks to ecosystems and fisheries under global warming. The temperature dependence of biological processes and regional differences in food web structure are two important sources of uncertainty and variation in climate forced projections of fish communities, but we do not know their magnitude or relative contribution. Here we systematically evaluated a range of different assumptions about temperature‐dependence on rates, including size‐dependent effects, controlling food intake, metabolism, and non‐predation mortality in fishes using species‐resolved size spectrum food web models that link individual‐level physiological processes to population and community dynamics. We simulated the physiological effect of warming in a range of size‐structured food web models calibrated to different marine ecosystems and in simplified trait‐based models. Higher food intake in warmed conditions increased total fish biomass, catches, and mean body weight, but these effects were offset by the negative effects of warming on metabolism and mortality, which combined resulted in lower total biomasses and catches for most food webs. These effects were enhanced when warming increased metabolic rates more than food intake, and the outcomes were also sensitive to size dependency of temperature responses. Importantly, these general patterns were not uniform across all food webs—individual functional groups and fish species within food webs responded to warming in different ways depending on their position in the food web and its structure. Hence, caution is warranted when generalizing food web or species outcomes to warming because they are mediated by community interactions. Uncertainty related to temperature dependence and ecological interactions will impact food web projections and should be represented in climate change projections.

Brobdingnagians and Goliaths: two forms of gigantism in fish.

Two forms of gigantism are differentiated in fish, Brobdingnagian and Goliathan gigantism, the former applying to populations whose individuals are all larger than is typical for the taxon, the latter to single individuals within a population. While Brobdingnagian gigantism is largely explained by various ecological and evolutionary rules, Goliathan gigantism is not. A mechanistic hypothesis is proposed which explains Goliathan gigantism in terms of the reduction of oxygen requirements of individual fish via moving to cooler temperatures and/or acquiring larger, more energy-dense prey, which enable them to get bigger, and, in the process, sometimes generate bimodal size distributions that may qualify as gradual forms between Goliathan and Brobdingnagian gigantism. This mechanism, which relies on the manner in which their gill surface area grows, is more likely to operate in fish that can get big in the first place than in fish that remain small.

Use of the raw material base of marine fish in Russian waters of the Far Eastern seas and adjacent areas of the open part of the Pacific Ocean in 2000–2020

The purpose of the work: characteristics of the raw material base of marine fish in the Far Eastern fishery basin and an assessment of the effectiveness of its use by domestic fisheries at the present stage (2000–2020).Methods used: to achieve this goal, data on biomass, catch and development of the main commercial marine fish were analyzed. Fish catches were reviewed based on operational information about the fishery based on daily ship reports from the industry monitoring system.Novelty: elements of novelty are generalized modern materials on biomass, catch and development of marine fish resources in the Far Eastern seas and adjacent waters of the Pacific Ocean. The current state of commercial fish stocks (walleye pollock, Pacific cod, saffron cod, Pacific herring, Righteye flounders, greenlings, Japanese pilchard, Chub mackerel, Pacific saury) in the Far Eastern fishing basin can be characterized as stable, and the distribution of the catch of these objects among individual fishing areas due to their significant volumes is practically determines the distribution of catch of both quota and non-quota species of marine fish. Scientific information support for the above-m entioned fish is at a high level, their biological condition is generally favorable, and the dynamics of their numbers is regulated mainly by habitat variability.Practical significance: the results of this study can be used in forecasting the dynamics of aquatic biological resources, and the results obtained on marine fish stocks and fisheries will improve the efficiency of using their raw material base.

Environmental and ecological risk of microplastics in the surface waters and gastrointestinal tract of skipjack tuna (Katsuwonus pelamis) around the Lakshadweep Islands, India.

The presence of microplastics (MPs) in marine ecosystems is widespread and extensive. They have even reached the deepest parts of the ocean and polar regions. The number of articles on plastic pollution has increased in recent years, but few have investigated the MPs from oceanic islands which are biodiversity hotspots. We investigated the possible microplastic contamination their source and characteristics in surface waters off Kavaratti Island and in the gastrointestinal tract (GT) of skipjack tuna, Katsuwonus pelamis collected from Kavaratti Island of the Lakshadweep archipelago. A total of 424 MP particles were isolated from the surface water samples collected from off Kavaratti Island with an average abundance of 5 ± 1nos./L. A total of 117 MPs were recovered from the GT of skipjack tuna from 30 individual fishes. This points to a potential threat of MP contamination in seafood around the world since this species has a high value in local and international markets. Fiber and blue color were the most common microplastic morphotypes and colors encountered, respectively, both from surface water and GT of fish. Smaller MPs (0.01-1mm) made up a greater portion of the recovered materials, and most of them were secondary MPs. Polyethylene and polypropylene were the most abundant polymers found in this study. The Pollution Load Index (1.3 ± 0.21) of the surface water and skipjack tuna (1 ± 0.7) indicates a minor ecological risk for the coral islands, while the Polymer Hazard Index highlights the ecological risk of polymers, even at low MP concentrations. This pioneer study sheds preliminary light on the abundance, properties, and environmental risks of MPs to this highly biodiverse ecosystem.

Elevational patterns of fish functional and phylogenetic community structure in a monsoon climate river basin

AbstractAimUnderstanding the patterns and drivers of biodiversity across space and time is commonly based on species diversity, which may ignore species' functional role and evolutionary history and result in an incomplete understanding of community assembly. It is suggested that integrating species, functional, and phylogenetic diversity could provide a more holistic assessment of community assembly in natural ecosystems. This study aimed to explore the elevational patterns and environmental drivers of multiple facets of fish diversity and community structure in a subtropical river during the wet and dry seasons.LocationThe Chishui River basin, China.MethodsWe investigated the responses of fish species richness, functional richness, and phylogenetic diversity to elevation in different seasons. Moreover, we compared functional dispersion and mean pairwise distance with those obtained from null models to infer assembly mechanisms shaping community structure. Additionally, we examined the environmental drivers (e.g. water chemistry, temperature, and river size) of fish diversity and community structure.ResultsFish species richness, functional richness, and phylogenetic diversity showed a negative relationship with elevation in the Chishui River basin. Fish communities tended to be on average functionally random but phylogenetically clustered. Furthermore, phylogenetic structure exhibited a decreasing pattern along the elevational gradient. Despite no significant seasonal changes for fish diversity (except for phylogenetic diversity), fish communities became more phylogenetically overdispersed and clustered at low and high elevations in the dry season. Additionally, the responses of fish diversity and community structure to environmental variables were not synchronous.ConclusionsAt the basin scale, environmental filtering was prevalent in shaping fish phylogenetic structure, whereas stochasticity was likely more important for functional structure. Moreover, the ecological mechanisms shaping individual fish communities switched from limiting similarity to environmental filtering as elevation increased, and the underlying forces at two ends of the elevational gradient became more prominent in the dry season.

Modeling Fetal Alcohol Spectrum Disorders in Zebrafish to Characterize the Impact of an Adverse Embryonic Environment on Adult Social Behavior.

Fetal alcohol spectrum disorders (FASD) describe all alcohol-induced birth defects. Birth defects such as growth deficiencies, craniofacial, behavioral, and cognitive abnormalities are associated with FASD. Social difficulties are common behavioral abnormalities associated with FASD and often result in serious health issues. Animal models are critical to understanding the mechanisms responsible for ethanol-induced social defects. Zebrafish are social vertebrates that produce externally fertilized transparent eggs; these characteristics provide researchers with a precise yet simple procedure for creating the FASD phenotype and an innate behavior that can be leveraged to model the social deficits associated with FASD. Thus, zebrafish are ideal for characterizing the social deficits of FASD. The goal of the current protocol is to provide the user with a simple behavioral assay that can be used to characterize the consequences of a negative environment early during development and the effects it can have on social behavior in adulthood. The protocol can be used to characterize the effect mutations or teratogens have on adult social behavior. The protocol outlined here demonstrates how to characterize the social behavior of individual fish during a 20-min social assay. Furthermore, the data obtained using the current protocol provides evidence that the protocol can be used to characterize the effects of embryonic ethanol-induced social defects in adult zebrafish.

The enigmatic occurrence, size distribution, and significance of a new macrourid species, Nezumia armentrouti, based on otoliths from the Lincoln Creek Formation (upper Oligocene Section), Washington State, USA

ABSTRACT Teleostean otoliths (112 sagittae) from the Lincoln Creek Formation (upper Oligocene), Washington State, U.S.A., were identified as Nezumia armentrouti n. sp. except for two specimens. The preponderance of one species (98.21%) is very unusual. Equally puzzling is the size of the otoliths that represents almost exclusively large, mature fishes (extant N. aequalis used as an analogue). Otoliths do not reflect various ages (sizes), and there appears to be an absence of larval, juvenile, or subadult representatives. The restricted range (97.32% of specimens 8.1–16.1 mm) of the otolith lengths (and corresponding fish length) is attributed to depth stratification, which is well-known in extant macrourids. Otoliths may be the result of piscivorous predators and subsequent excretion. However, the unusual occurrence of the otoliths (single, or at most, two specimens often associated with thin bone beds) may indicate a different process such as the death and decay of individual fish. This investigation is highly significant on many fronts including the first fossil occurrence of the benthopelagic deep-sea Nezumia in North America (excluding the Caribbean), possible evidence of depth stratification in the paleoenvironment based on otolith length, and otoliths from an outer shelf/shelf break to upper slope paleoenvironment (200–600 m), which are extremely rare in the published fossil record.

Do captive fish need cognitive enrichment? A test with a puzzle feeder in guppies

AbstractFor many mammalian and avian species, it has been proposed that cognitive enrichment, such as puzzle feeders, can improve welfare in captive conditions. A well‐established method to evaluate the need for cognitive enrichment is to observe the preference of the animal between freely available food and a puzzle feeder. We investigated this preference in a teleost fish, the guppy. In most of our experimental trials, guppies first chose the feeder with freely available food over the puzzle feeder, in contrast with what was observed in most other species. Nevertheless, the guppies' number of choices for the puzzle feeder was significantly greater than zero. Moreover, after consuming the freely available food, most of the guppies tackled the puzzle feeder. This pattern of results suggests that guppies displayed a certain interest in the puzzle feeder that was overshadowed by their strong attraction towards the free food. Interestingly, several measures of performance indicated that female guppies responded more positively towards the puzzle feeder as compared to the males, suggesting sex differences in the preference for cognitive enrichment. In conclusion, our study highlights the potential significance of cognitive enrichment for captive fish. Considering that the number of individual fish maintained in captivity exceeds by far that of any other vertebrate group, it is paramount to investigate cognitive enrichment in other teleost species.

Size-dependence of food intake and mortality interact with temperature and seasonality to drive diversity in fish life histories.

Understanding how growth and reproduction will adapt to changing environmental conditions is a fundamental question in evolutionary ecology, but predicting the responses of specific taxa is challenging. Analyses of the physiological effects of climate change upon life history evolution rarely consider alternative hypothesized mechanisms, such as size-dependent foraging and the risk of predation, simultaneously shaping optimal growth patterns. To test for interactions between these mechanisms, we embedded a state-dependent energetic model in an ecosystem size-spectrum to ask whether prey availability (foraging) and risk of predation experienced by individual fish can explain observed diversity in life histories of fishes. We found that asymptotic growth emerged from size-based foraging and reproductive and mortality patterns in the context of ecosystem food web interactions. While more productive ecosystems led to larger body sizes, the effects of temperature on metabolic costs had only small effects on size. To validate our model, we ran it for abiotic scenarios corresponding to the ecological lifestyles of three tuna species, considering environments that included seasonal variation in temperature. We successfully predicted realistic patterns of growth, reproduction, and mortality of all three tuna species. We found that individuals grew larger when environmental conditions varied seasonally, and spawning was restricted to part of the year (corresponding to their migration from temperate to tropical waters). Growing larger was advantageous because foraging and spawning opportunities were seasonally constrained. This mechanism could explain the evolution of gigantism in temperate tunas. Our approach addresses variation in food availability and individual risk as well as metabolic processes and offers a promising approach to understand fish life-history responses to changing ocean conditions.

Precision of four calcified structures for age estimation of Black Carp

AbstractObjectiveBlack Carp Mylopharyngodon piceus is an emerging invasive species in North America with an expanding population in the Mississippi River basin. Current aging methods use a suite of structures for age estimation, and a single structure is needed to minimize processing time, to maximize consistency of age and growth measurements, and to allow for back‐calculation of individual fish length at age.MethodsIn total, 236 Black Carp were collected throughout the year from 2017 to 2019 through incidental captures by commercial fishers and biologists. In a subsample, 119 Black Carp from 429 to 1268 mm total length were compared for the precision of annuli counts by two experienced readers for the two anterior pectoral fin rays, the anterior dorsal fin ray, sectioned vertebrae, and lapilli otoliths based on percent exact agreement (PA), percent agreement within 1 year (PA ± 1), coefficient of variation (CV), and bubble plots. Consensus annuli counts were compared by PA and CV between structures. We applied annuli counts, as opposed to age, as fish were collected during all seasons and structures were examined independently by readers without knowledge of capture date.ResultVertebrae and dorsal rays had the highest PA between readers. Dorsal ray had the lowest CV and higher PA ± 1. Pectoral rays and lapilli otoliths had the lowest PA. Between‐structure consensus annuli counts indicated that pectoral rays and the dorsal ray annuli counts were the most similar (PA >70% and CV <12) and lapilli otoliths were the most dissimilar (PA >35% and CV >24). Reader‐reported confidence was highest for vertebrae, then in decreasing order, dorsal ray, pectoral rays, and lapilli otoliths. Lumens were present in all fin rays with only minor effects observed on annuli counts, aside from the anterior‐most pectoral fin ray, in which lumens obscured the presence of one or more potential annuli in 61% of structures.ConclusionThe dorsal ray had the highest agreement between readers, with agreement with ±1 year at 98%; the structure can be efficiently extracted and processed, and the structure's morphology and growth pattern are conducive to aging older fish. Vertebrae had high agreement between readers, but a systematic pattern of double bands in vertebrae increased the between‐reader variation in older fish as the interannual growth pattern compressed the viewable area; this was identified by readers based on aging criteria and highlights the need for training novice readers. Validation of annual growth in the tested suite of structures is still needed.

Assessing Impacts and Local Perceptions Following the Incidental Introduction of tilapia (Cichlidae: Cichliformes) in a Remote Inland Fishery in Papua New Guinea

Introductions of non-native fish are intended to have positive social outcomes, although they can also result in negative environmental consequences. Recently, incidental introduction of tilapia (Oreochromis cf. niloticus) was recorded in the Kikori River, Papua New Guinea. This study investigated the abundance of Oreochromis cf. niloticus relative to native fish species in the Kikori Town market, and interviewed market vendors to gauge the local perception of Oreochromis cf. niloticus. Market data were collected over eight days with 1474 individual fish observed. Oreochromis cf. niloticus comprised 11.4% (n = 168) of fish and was the largest contributor of biomass (40.2%). Market vendors reported that Oreochromis cf. niloticus was easy to catch and sell, and ranked it highly in sale preference compared to native species. There is potential to explore export markets for Kikori River Oreochromis cf. niloticus in PNG’s highland provinces to expand economic opportunities for local communities.

Morphological and molecular characterisation of Cymothoa eremita (Brunnich, 1783) (Isopoda: Cymothoidae) from the South China Sea

A morphological description and molecular characterisation of the parasitic isopod Cymothoa eremita Brünnich, 1783, collected off the fish host Nemipterus furcosus (Valenciennes, 1830) from the South China Sea, is presented here. Since most cymothoid descriptions are primarily based on females, this paper highlights the morphological characteristics from 20 ovigerous female and 20 male C. eremita cymothoids, isolated from 300 fish individuals. Furthermore, our findings indicated significant variations in the morphological features of C. eremita, including: 1) average length and width dimensions, 2) the presence or absence of eyes, 3) the length of pleotelson, 4) the configuration of its posterior and lateral margins, and 5) the structure of the cephalon. These characteristics were compared among diverse fish host species reported in different geographical regions. Twenty one of 300 N. furcosus were infested with C. eremita, with a prevalence of 7%, and mean intensity of 1.9 (two cymothoids per individual fish) respectively. A total of 687 base pairs (bp) from the mitochondrial cytochrome oxidase subunit I (COI) gene were sequenced for C. eremita as a complementary measure to the morphological analysis undertaken in this study. These sequences were utilized to reconstruct a phylogenetic tree, incorporating our sequenced specimens and relevant sequences sourced from the GenBank database. The Maximum Likelihood (ML) phylogenetic tree comprised 45 cymothoid species, with partial COI gene sequences showing monophyletic clustering of most species within the same genus, which is in congruence with their morphological divergence. Continued efforts to conduct studies on the biology, taxonomy, ecology and genetics of both cymothoid and fish host are crucial to better understand the patterns of host-parasite specificity and co-evolutionary changes, which may indirectly contribute towards cymothoid speciation and diversification.

Thermal tolerance and habitat preferences mediate how freshwater fish body sizes respond to warming

Recent studies have linked ecosystem warming to decreased mean body size in aquatic ectotherms but have often relied on experimental approaches. This study explores how climate change modifies adult body sizes in natural communities for five culturally, commercially, and recreationally important freshwater fish species that vary in thermal preferences (lake trout ( Salvelinus namaycush), lake whitefish ( Coregonus clupeaformis), walleye ( Sander vitreus), yellow perch ( Perca flavescens), and smallmouth bass ( Micropterus dolomieu)). Using data for >170 000 sampling records from >600 lakes spanning the entire province of Ontario, Canada, we employ a spatial analysis technique based on Integrated Nested Laplace Approximation to detect body size changes due to warming lake conditions. With warming conditions, cold-adapted species (lake whitefish) decreased in adult body size, while cool- and warm-adapted species (walleye and smallmouth bass) increased in adult body size. Our study, like others recently conducted in marine and freshwater systems, demonstrates that the responses of fish body sizes to warming are not a unidirectional shift and may be linked to the habitat and thermal preferences of individual fish species.

A semi-automated spectral approach to analyzing cyclical growth patterns using fish scales.

We introduce a new semi-automated approach to analyzing growth patterns recorded on fish scales. After manually specifying the center of the scale, the algorithm radially unwraps the scale patterns along a series of transects from the center to the edge of the scale. A sliding window Fourier transform is used to produce a spectrogram for each sampled transect of the scale image. The maximum frequency over all sampled transects of the average spectrogram yields a well-discriminated peak frequency trace that can then serve as a growth template for that fish. The spectrogram patterns of individual fish scales can be adjusted to a common period accounting for differences in date of return or size of fish at return without biasing the growth profile of the scale. We apply the method to 147 Atlantic salmon scale images sampled from 3 years and contrast the information derived with this automated approach to what is obtained using classical human operator measurements. The spectrogram analysis quantifies growth patterns using the entire scale image rather than just a single transect and provides the possibility of more robustly analyzing individual scale growth patterns. This semi-automated approach that removes essentially all the human operator interventions provides an opportunity to process large datasets of fish scale images and combined with advanced analyses such as deep learning methods could lead to a greater understanding of salmon marine migration patterns and responses to variations in ecosystem conditions.

Optimizing the prediction of discard survival of bottom-trawled plaice based on vitality indicators.

Predicting the discard survival of aquatic animals after fisheries capture using vitality indicators (i.e. individual scores or indices of physical condition) is a resource-efficient approach compared to estimating discard survival from captive observation. But such indicators do not always lead to accurate and robust predictions. Individual scores of reflex impairments and injuries are typically given the same weight when being aggregated into an index, while some reflexes or injuries may contribute to mortality more than others. This study established an analytical methodology and created an index based on differential contributions of individual reflexes and injuries to optimize the prediction of discard survival of bottom-trawled European plaice (Pleuronectes platessa). The optimization procedures were applied to a dataset from vitality assessment of 1122 undersized plaice caught during 16 commercial fishing trips and 58 gear deployments in Belgium and Denmark. As welfare indicators, we considered and evaluated against post-capture survival of plaice: original vs. optimized reflex impairment and injury (R&I) index, number of absent reflexes, number of present injuries, number of absent reflexes and present injuries, categorical vitality score and individual reflex and injury scores. These were used in eight candidate generalized linear models (one without any vitality indicator) as explanatory variables to predict survival, with or without biological, environmental, technical and operational covariates, either at the individual fish or trip level. Bruising to the head and body were the most relevant predictors. The optimized R&I index did not perform better than any other vitality indicator, and all the indicators performed poorly in predicting survival probability both at the fish and trip levels without information on air exposure and seawater temperature. This means that they cannot be considered to be independent measures. The categorical vitality score provided a viable alternative to the more labour-intensive, scoring method of reflex responsiveness. Use of reflexes as proxies may not be accurate when they are not independent of environmental, biological or technical variables.