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Globally, marine fish communities are being altered by climate change and human disturbances. We examined data on global marine fish communities to assess changes in community‐weighted mean temperature affinity (i.e., mean temperatures within geographic ranges), maximum length, and trophic levels, which, respectively, represent the physiological, morphological, and trophic characteristics of marine fish communities. Then, we explored the influence of climate change and fishing on these characteristics because of their long‐term role in shaping fish communities, especially their interactive effects. We employed spatial linear mixed models to investigate their impacts on community‐weighted mean trait values and on abundance of different fish lengths and trophic groups. Globally, we observed an initial increasing trend in the temperature affinity of marine fish communities, whereas the weighted mean length and trophic levels of fish communities showed a declining trend. However, these shift trends were not significant, likely due to the large variation in midlatitude communities. Fishing pressure increased fish communities' temperature affinity in regions experiencing climate warming. Furthermore, climate warming was associated with an increase in weighted mean length and trophic levels of fish communities. Low climate baseline temperature appeared to mitigate the effect of climate warming on temperature affinity and trophic levels. The effect of climate warming on the relative abundance of different trophic classes and size classes both exhibited a nonlinear pattern. The small and relatively large fish species may benefit from climate warming, whereas the medium and largest size groups may be disadvantaged. Our results highlight the urgency of establishing stepping‐stone marine protected areas to facilitate the migration of fishes to habitats in a warming ocean. Moreover, reducing human disturbance is crucial to mitigate rapid tropicalization, particularly in vulnerable temperate regions. [ABSTRACT FROM AUTHOR]

In the context of aquaculture, fish length is a key parameter to assess fish stocks, essential for feeding regime and contributes for decisions at several production levels. However, taking length measurements is a cumbersome task that, when applied to living individuals, can induce considerable stress, increasing the risk of damage or hindering their growth. Computer vision is one of the most used non-contact tools to overcome this issue, being fast, consistent and repeatable. However, its use in aquatic environments is limited by the high cost, the difficulty of calibrating the system in underwater conditions and the complexity of implementation. This paper proposes a low-cost easy-to-use vision system that can take measurements on live fish in aquatic conditions, without the need for a special calibration or a demanding in-water calibration service. The present work implemented a compact stereo vision system and developed a method that estimates the correct length of fish, based on the variation of the angle of incidence of the light rays in the water. Given some structural conditions such as a short baseline, the system is able to measure fish with an error of less than 1%. The short baseline allows to have a compact system and reduces the effect of water refraction on the 3D reconstruction. A set of experiments were performed with real fish, working robustly for a set of orientations of the fish (even when the caudal fin and snout are on different distances to the cameras). [ABSTRACT FROM AUTHOR]

The Lower Mississippi River has a floodplain that includes >1350 perennial lakes carved by shifts in river courses and other hydro‐fluvial processes over eons. Notwithstanding their similar provenances, these waterbodies exhibit an immense variety of morphologies and successional stages that illustrate their natural trajectory from aquatic to forested wetlands. A result of this geographical, morphological and temporal diversity is dynamic and varied fish communities. We examined how size structures of fish communities in these floodplain lakes were associated with key in‐lake and off‐lake environmental drivers.Fish lengths were collected with standardised procedures in a sample of 30 of these lakes to construct a lake‐by‐length group matrix. Likewise, in‐lake and off‐lake environmental descriptors were collected to construct a lake‐by‐covariate matrix. Distance‐based linear models were used to assess associations between fish size structure and environmental descriptors.Smaller fish were typically associated with increasing levels of turbidity, chlorophyll‐a, phycocyanin and surrounding agriculture. Shallow, hypereutrophic floodplain lakes associated with agricultural landscapes and reduced connectivity experience harsh physicochemical environments. These conditions appeared to hinder the formation of sustained fish communities but may confer a survival advantage to juveniles or small short‐lived species. Conversely, larger fish were associated with increasing lake depth, water clarity, connectivity, and extent of surrounding forests‐wetlands. Enhanced stability and size structure were observed in communities residing in deeper and clearer lakes, suggesting that these conditions facilitated the development of longer‐lived species spanning multiple age groups. The enhanced connectivity that facilitated this increased stability also permitted the presence of larger itinerant species.Size‐structure assessments can serve as a valuable ecological and biodiversity indicator in floodplain lakes.Size‐structure assessments could supplement and, depending on objectives, even supplant conventional taxonomic analyses, and enhance surveillance of this vast and important natural resource. [ABSTRACT FROM AUTHOR]

Objective: Effective policy formulation regarding the conservation of freshwater fish necessitates an understanding of water‐specific prevailing conditions and trends. Assessing fish populations in inland waters is difficult and expensive because there are many independent systems that need to be evaluated. Therefore, numerous freshwater systems are beset by insufficient data and the lack of systematic assessments of their status. To alleviate this deficiency, the objective of this study was to review length‐based metrics that may have utility in evaluating the well‐being of freshwater fish populations. Methods: Length measurements can serve as proxies for a range of ecological and population dynamics attributes that are essential for the effective management of fish and associated fisheries. A review of the historical development of length measurements in fish conservation is provided, along with an examination of the potential biases that may arise from the use of lengths in practical contexts. In addition, we examine techniques that enable the spatial and temporal visualization of length data sets, as well as a range of indices and metrics that can be computed using length measurements. Result: Building populations assessments around length may be a cost‐effective strategy that allows a first cut at managing a large number of waters. Length‐based assessments can signal if management intervention is necessary, if management policies are yielding the intended outcome, or if surveys beyond mere length are necessary. Conclusion: Our review indicates that length offers a straightforward and efficient approach to evaluate the status of fish populations in inland systems. We encourage pursuing additional study and to this end propose specific areas for investigation. Impact StatementThis paper reviews methods, indices, and criteria suited for monitoring the status of fish populations in inland systems based on body length data. Building population assessment strategy around length can be cost‐effective with only minimal data requirements. [ABSTRACT FROM AUTHOR]

In the context of aquaculture, fish length is a key parameter to assess fish stocks, essential for feeding regime and contributes for decisions at several production levels. However, taking length measurements is a cumbersome task that, when applied to living individuals, can induce considerable stress, increasing the risk of damage or hindering their growth. Computer vision is one of the most used non-contact tools to overcome this issue, being fast, consistent and repeatable. However, its use in aquatic environments is limited by the high cost, the difficulty of calibrating the system in underwater conditions and the complexity of implementation. This paper proposes a low-cost easy-to-use vision system that can take measurements on live fish in aquatic conditions, without the need for a special calibration or a demanding in-water calibration service. The present work implemented a compact stereo vision system and developed a method that estimates the correct length of fish, based on the variation of the angle of incidence of the light rays in the water. Given some structural conditions such as a short baseline, the system is able to measure fish with an error of less than 1%. The short baseline allows to have a compact system and reduces the effect of water refraction on the 3D reconstruction. A set of experiments were performed with real fish, working robustly for a set of orientations of the fish (even when the caudal fin and snout are on different distances to the cameras).

Purpose: The influence of two key factors, host length and infection site, on the host-parasite interaction in Ompok bimaculatus (Butter catfish) from Mukutmanipur Dam Lake, were investigated. Methods: Present study involved 192 specimens of Ompok bimaculatus with varying body lengths, subjected to diverse statistical analyses. One-way analysis of variance (ANOVA) was performed for the parasite numbers for three groups (cestode, nematode and trematode). Subsequently, we conducted one-way permutational multivariate analysis of variance (PERMANOVA) followed by pairwise test to assess parasite numbers across three body sites (intestine, mesentery, and bodycavity), employing the Bray-Curtis index. Additionally, Principal Coordinate Analysis (PCoA) for the same dataset was performed using the same index. Linear regression analysis was performed for the fish length-cestode number, fish length-nematode number, fish length-trematode number and fish length-total parasite number. Results: One-way ANOVA revealed no significant differences in parasite numbers among the three endo-helminth groups (cestode, nematode, and trematode). The results of PERMANOVA revealed significant differences in parasite numbers across the three body sites of the host fishes (groups) (F = 9.41, p = 0.0001). Pairwise tests further demonstrated significant differences between the intestine-mesentery, intestine-body-cavity, and mesentery-body-cavity. Additionally, Principal Coordinate Analysis (PCoA) unveiled a significant relationship between infection site and parasite number. However, linear regression analysis examining the relationship between fish length and parasite abundance indicated no significant associations. Conclusions: Through a detailed exploration of the statistical analyses, we provide insights into the host-parasite interaction, elucidating both established knowledge and novel findings in fish parasitology. [ABSTRACT FROM AUTHOR]

This study aimed to identify a new feed for Catla catla post larvae. There is no suitable feed in Sri Lanka for post-larvae of Indian carp. A complete randomized design was used. Two feeds were formulated using different nutrient compositions with 32 % and 25 % of the fish meal separately. The formulated feeds were used as treatment one and treatment two. Commercial feed was used as the control. Catla catla post-larvae were stocked at a density of 300 post larvae per m2 in nine cement tanks. Growth parameters were measured every two other days. Feeds were formulated according to the nutrient requirement of Catla catla post larvae. Water quality parameters were measured daily to maintain the water quality at the proper level. T-test preformed in Mini tab 16.0. Total body weight and length were significantly different (p

The relationship between fish total length and otolith length, width, and weight were inspected in the golden grey mullet, Chelon auratus, collected from the Mediterranean Sea coast of Libya and Ain Ziana, an inland lagoon located northeast of the Libyan coast. Chelon auratus is considered a valuable marketable fish in Libya. The main aim of the study was to estimate the statistical relationship between fish total length and the otolith length, width, and weight. This information will be noteworthy in the upcoming analyses on the biology of this species, which will provide critical information about feeding, age and growth of this species. Linear and non-linear regression models were used. The regression equations for each locality were significantly different, with exception of the right and left weight of individuals collected from the Mediterranean Sea coast as well as for the Ain Ziana Lagoon. The regression relationships were more homogeneous in Ain Ziana Lagoon than in the Mediterranean Sea, where there was greater variation in total length and otolith characteristics. The results obtained from this investigation were the first to address the relationship between otolith morphometric and total length for golden grey mullets collected from two localities in the Libyan waters. [ABSTRACT FROM AUTHOR]

This study aimed to identify a new feed for Catla catla post larvae. There is no suitable feed in Sri Lanka for post-larvae of Indian carp. A complete randomized design was used. Two feeds were formulated using different nutrient compositions with 32 % and 25 % of the fish meal separately. The formulated feeds were used as treatment one and treatment two. Commercial feed was used as the control. Catla catla post-larvae were stocked at a density of 300 post larvae per m2 in nine cement tanks. Growth parameters were measured every two other days. Feeds were formulated according to the nutrient requirement of Catla catla post larvae. Water quality parameters were measured daily to maintain the water quality at the proper level. T-test preformed in Mini tab 16.0. Total body weight and length were significantly different (p<0.05). The survival percentage was higher in T1. Treatment feeds were not affected by the water quality parameters. Catla catla post-larvae show a maximum increase in length, survival percentage and weight in T1. It was concluded that T1 has a good combination of fish meal for Catla catla post-larvae. This study will help in future feed formulation for post-larvae feeds in developing nations. [ABSTRACT FROM AUTHOR]

In 2012, the fishway in the Miyanaka Intake Dam in Niigata Prefecture, Japan, was reconstructed and divided into three fishways (ice‐harbor‐, stair‐, and rock‐ramp‐type) with different flow velocities and water depths. We conducted an adaptive monitoring survey in these fishways from 2012 to 2020, and 33 fish types were found, including migratory, swimming, small swimming, and benthic fishes. Many species displayed a preference for specific fishways. The run‐up for Tribolodon hakonensis was studied to determine the effects of physical parameters such as body length, rush speed for instantaneous swimming, water temperature, and presence/absence of nuptial coloration on fishway preference. T. hakonensis with nuptial coloration had greater body length and higher rush speeds than those without it. They also preferred the ice‐harbor fishway, whereas their shorter, uncolored counterparts preferred the stair and rock‐ramp alternatives. The environmental conditions selected by T. hakonensis changed according to their growth stage, as did fishway preference. Changes in fishway environmental conditions may have influenced the observed differences in fishway populations. It was thus confirmed that developing fishways with different flow velocities and water depths is effective in supporting the various life stages of T. hakonensis. [ABSTRACT FROM AUTHOR]

We explored intraspecific relationships between biochemical and morphometric traits among sixteen fish species from the Canadian waters of the Laurentian Great Lakes. We focused on hypotheses linking two morphometric descriptors (fish length and condition factor, CF, the latter derived from species-specific allometric-growth equations) to lipid content and polyunsaturated fatty acid (PUFA) composition of dorsal muscle tissue. Each population from each of the lakes was assumed to display different relationships. All correlations were better represented by linear than non-linear relationships. Interspecific and among lakes differences accounted for most of the registered variability of fatty acid (FA) composition. Once these two covariates were parsed out, there was a discernible intraspecific coupling between fish length, CF, and fish biochemical traits, including positive correlations with muscle lipid and PUFA composition. The sign of the correlations was consistent among different populations, aligned with the theoretical expectations, and with interspecific trait correlations. However, for some species, correlations could be positive in one lake but negative in another, suggesting that local environmental variations could affect biochemical rates. We also found three trends associated with the rate at which different fatty acids accumulate in fish muscle tissue that are potentially related to food availability. These relationships between CF and FA composition provide a promising starting point to establish efficient, cost-effective, field-based estimates of essential FA descriptors. In this vein, we present a user-friendly application for the estimation of lipid content and PUFA composition, based solely on weight and length, that any angler and/or citizen-science participant can easily obtain. [ABSTRACT FROM AUTHOR]

Arctic char (Salvelinus alpinus) is a top predator and the most widespread fish in Arctic lakes. The presence of Arctic char affects the predator–prey dynamics of the key species in the food webs in these lakes. This study sought to elucidate the effects of habitat (littoral, pelagic, or profundal) and lake morphometry on the trophic position of this char in the food web. Using stomach content and stable isotope analyses, we investigated the effect of fish length, habitat, and time (individual survey years: 2008, 2013, 2018, and 2019) on the dietary niches of landlocked Arctic char populations during summer in two west Greenland lakes: Badesø (area 0.8 km2, mean depth 9.2 m) and Langesø (area 0.3 km2, mean depth 5.0 m). The small char (<20 cm fork length) in Badesø generally foraged less littoral macroinvertebrates than those from Langesø. The large chars were mainly piscivorous in both lakes. In Badesø, there was a shift from relying on littoral to pelagic invertebrates by the small char from 2008–2013 to 2018–2019. The proportionally larger size of the littoral habitat in the smaller Langesø led to an increased reliance on littoral-derived macroinvertebrates in the diet of the small char, more so than in the larger Badesø, where the predominant reliance was on pelagic sources. [ABSTRACT FROM AUTHOR]

Fisheries are of immense importance to Mediterranean countries, for protein, employment and livelihoods. Studies addressing the factors affecting fish price dynamics are of interest to examine their drivers as prices often dictate target fisheries. This study investigates fish market prices in relation to landings and fish sizes from Türkiye's largest fish market in Istanbul as the study site. A total of 39 wild marine taxa were examined for their landed catch (kg) and average prices (per unit/TRY) from 2006 to 2019. We found fish prices increased from small pelagic to medium pelagic to demersal fish.GAMmodel results for inter-species tests showed a strong positive effect of local maximum length (p<0:01) and a weaker positive effect of trophic level and vulnerability (p<0:1) on fish market price, but that landings amounts have no significant effect as a single predictor. Monthly price variations of bluefish and bonito were completely different than other species dynamics, as the last substantial commercial medium pelagic fish species left; highest monthly prices were related to the highest monthly landings for bonito and for the non-closure period for bluefish. Market prices as economic indicators for fisheries may have the potential to reveal ecosystem variations as well as socioeconomic drivers. Databases including extensive data for key fish sales centers can be used to help understand fishery dynamics from an ecosystem perspective, especially for data-poor regions like Türkiye. [ABSTRACT FROM AUTHOR]

Fisheries are of immense importance to Mediterranean countries, for protein, employment and livelihoods. Studies addressing the factors affecting fish price dynamics are of interest to examine their drivers as prices often dictate target fisheries. This study investigates fish market prices in relation to landings and fish sizes from Türkiye’s largest fish market in Istanbul as the study site. A total of 39 wild marine taxa were examined for their landed catch (kg) and average prices (per unit/TRY) from 2006 to 2019. We found fish prices increased from small pelagic to medium pelagic to demersal fish. GAM model results for inter-species tests showed a strong positive effect of local maximum length (p

A procedure is proposed to assess the impact of various relationships found in the literature and is used to convert acoustic target strengths (TS) to fishes' total length (TL) with respect to the compatibility of fish length data obtained from vertical hydroacoustics and gillnets. The study used one set of data collected with a 120 kHz echosounder across the mesotrophic, dimictic Lake Dejguny. Four general multi-species TS–TL relationships were tested for the maximum dorsoventral characteristic: (1) a relationship developed using mainly West Atlantic marine and brackish water fish for various frequencies, (2) a relationship developed using fish from the Salmonidae, Percidae, and Cyprinidae families at 120 kHz, as well as the relationship shown by two generalized equations for representatives of (3) the Cyprinidae family (200 kHz) and (4) the Percidae family (200 kHz). In addition, two other equations were developed for (5) perch (Perca fluviatilis) and (6) roach (Rutilus rutilus). The procedure for selecting the most appropriate TS–TL ratio began by determining the TS threshold that would eliminate small fish that were ineffectively caught with gillnets. Depending on the TS–TL relation, the threshold ranged from −48.5 dB to −45.5 dB, and the corresponding TL was in the range of 62.3–93.0 mm. Then, using linear regression, the relationship between the percentage of caught fish organized in length classes (TL), whose boundaries were determined using the tested TS–TL relationships, and the share of fish recorded acoustically in the corresponding TS classes (with a 1.5 dB interval) was examined. The fit of the regression model to the data (percentage) was assessed using the coefficient of determination r2, the mean absolute error (MAE), the Nash–Sutcliffe model efficiency coefficient (NSE), and root mean square error (RMSE). For the data from Lake Dejguny, the most similar distribution of fish echo proportions and the corresponding distribution of total length (TL) for fish larger than 62 mm were obtained using the TS–TL relation developed using fish from the Salmonidae, Percidae, and Cyprinidae families (2), and for fish larger than 74 mm, the relation was developed for the family Pericidae (4). No evidence was found to unambiguously verify the meanings of different sound frequencies (120 and 200 kHz) for which the TS–TL relationships used in the analysis were derived. The proposed procedure can be used to select the optimal regression equation. [ABSTRACT FROM AUTHOR]

In this paper, we compile estimates of cod size distributions based on zooarchaeological data and contemporary lengthfrequency data to look at variability in size composition through time across the North Pacific, from the northern Kuril Islands through the Aleutian Islands to southeast Alaska. The results suggest that a strong longitudinal trend in cod size has remained consistent over time, with the largest cod found to the west. We find that five of nine sites show that overall cod length and distribution of the largest fish remain relatively unchanged. Two sites wherewe find truncation of the length distributions-or loss of the largest fish-are places where the modern fisheries have the longest history and have been most intense, suggesting a potential for anthropogenic impacts on these local populations. We acknowledge two limitations in these data: (1) there are differences in selectivity between the ancient and modern fisheries; and (2) seasonal variability in fish availability was observed to be an important explanatory variable in the modern data set, but the season of harvest is poorly understood for the ancient collections. Therefore, while differences observed between the two data sets suggest possible anthropogenic influence on the size structure of Pacific cod, they are not conclusive. [ABSTRACT FROM AUTHOR]

Relationships between fish length and otolith length, width and mass were examined in the Australian anchovy Engraulis australis (White, 1790) recovered from the food of Gannet examined from colonies at islands of Horuhoru Rock and Mahuki Islands in the Hauraki Gulf. New Zealand. The relationships between otolith length- fish total length (TL), otolith-weight-TL, and otolith-width-TL were investigated by means of non-linear regression models (TL = 0.54 OL 16.86, TL = 4.39 OW 7.61 and TL = 26.19 OWe 2.2). This study characterizes the first reference available on the relationship of fish size and otolith size and weight for E. australis obtained from bird’s food in the Pacific Ocean region.

Aphanius hormuzensis is an endemic tooth‐carp found in the Hormuzgan drainage in S‐Iran. This study aimed to investigate the size‐dependent alternations of scale surface ornamentation in this species by conducting scanning electron microscopy and morphological analysis. A total of 50 wild fish individuals were captured from Shur River, and were classified into five size classes based on the standard length; SC–I (SL = 10–20 mm), SC–II (SL = 21–30 mm), SC–III (SL = 41–50 mm), SC–IV (SL = 51–60 mm), and SC–V (SL = 61–70 mm), and their scales were removed from below the dorsal fin (key scale) and caudal peduncle regions. The results revealed a clear trend of scale structural development in A. hormuzensis. The scale of small‐sized (TL < 30 mm) and large‐sized fishes (TL > 30 mm) differed, respectively, in the following characters; the overall shape (often circular vs. polygonal), relative focus size (large, FL/SL = 440–610 μm vs. intermediate and small, FL/SL = 100–330 μm), types of radii (only primary vs. three types), relative radii length (short, RL/SL = 100–180 μm vs. long, RL/SL = 320–450 μm), lepidont (absent or undeveloped vs. present and developed), and the relative lepidont length (short, LL/SL = 0.83–0.90 μm vs. intermediate and long, LL/SL = 1.2–2.2 μm). These character alternations could explain certain developmental stages in this species. The size‐dependent changes in the surface micro‐ornamentations as shown in this study suggest that these characters should be used cautiously for taxonomic studies of the aphaniid fishes. [ABSTRACT FROM AUTHOR]

Relationships between fish length and otolith length, width and mass were examined in the Australian anchovy Engraulis australis (White, 1790) recovered from the food of Gannet examined from colonies at islands of Horuhoru Rock and Mahuki Islands in the Hauraki Gulf, New Zealand. The relationships between otolith length-fish total length (TL), otolith-weight-TL, and otolith-width-TL were investigated by means of non-linear regression models (TL = 0.54 OL 16.86, TL = 4.39 OW 7.61 and TL = 26.19 OWe 2.2). This study characterizes the first reference available on the relationship of fish size and otolith size and weight for E. australis obtained from bird's food in the Pacific Ocean region. [ABSTRACT FROM AUTHOR]

The Barents Sea is a nursery area for many commercially and ecologically important fish stocks, and this whole region is presently subject to rapid climatic change from a cold period in the 1980s to a record warm period in the latest decade, with a peak in 2016. The present study focuses exclusively on year 2016, which was characterized by record warm air and seawater and an exceptionally large horizontal coverage of Atlantic waters. Earlier studies have suggested that environmental conditions during the first year of life are the most critical for year class strength and development of fish stocks. We focus on 8 fish species (age 0) and document spatial distributions of their abundances and lengths as well as ambient environmental conditions. Data for most of the Barents Sea obtained from the ecosystem survey (BESS) were used to explore if the record-warm conditions in 2016 limited 0-group fish distributions, abundances and size. Abundances and lengths for the 8 species were related to physical conditions (seawater temperature and salinity) and biological features (biomass of mesozooplankton and biomass of the jellyfish). In 2016, 0-group capelin, haddock, herring and long rough dab were more abundant and all species except long rough dab were larger than the long term mean (1980–2015). Larger individuals and higher abundances were observed mainly in the areas covered by relatively warm water masses apparently holding a sufficient amount of plankton. Most of the 0-group fishes were distributed within their thermal habitats, but with some geographical shift most likely reflecting a shift in the distribution of water masses. A significantly lower abundance of polar cod was observed in 2016, with very few individuals registered within the traditional core area in the south eastern Barents Sea. The increased temperature and low plankton biomass may have limited polar cod distribution and abundance there. A spatial analysis showed that biomass of C. capillata was positively related to abundances of 0-group herring, capelin and cod, indicating that they were inhabiting similar water masses. The high abundances of capelin, haddock, herring and long rough dab, and generally large individuals of most species, may suggest suitable living and feeding conditions in 2016.

Imaging sonars are used around the world for fish population monitoring. The accuracy of the length measurements has been reported in multiple studies for relatively short (<15 m) ranges and high image resolution. However, imaging sonars are often used at longer ranges (i.e., >15 m) where the images produced from sonar returns become less detailed. The accuracy of the length measurements from the Adaptive Resolution Imaging Sonar (ARIS) was tested by releasing n = 69 known‐sized adult Atlantic salmon (Salmo salar) directly into the sonar field at ranges between 15 and 29 m, and measuring their echoes manually by four users and semi‐automatically using a computer workflow in Echoview software. Overall, the length measurements were very variable: compared to true (fork) lengths, the mean of differences varied between −9.9 cm and 7.8 cm in the human‐generated datasets, and between −42.8 cm and −20 cm in the computer‐generated dataset. In addition, the length measurements in different datasets were only in poor or moderate agreement with each other (intraclass correlation <0.61). Contrary to our expectations, the distance from the transducer or the subjectively assessed echo quality did not have an effect on the measurement accuracy in most of the datasets and when it did, the effect was not systematic between the datasets. Therefore, a size class and length prediction model was implemented in a Bayesian framework to group salmon into two size categories: One‐Sea‐Winter (<63 cm) and Multi‐Sea‐Winter (≥63 cm) groups. The model correctly predicted the size category in 83% of the fish in the computer‐generated dataset and ranged from 68% to 74% in the human‐generated datasets. We conclude that fish length measurements derived from long‐range imaging sonar data should be used with caution, but post‐processing can improve the usefulness of the data for specific purposes, such as adult Atlantic salmon population monitoring. [ABSTRACT FROM AUTHOR]

• The abundance of a monogenean parasite was compared between native and invasive host ranges. • The effects of host length, water temperature and month of the year on parasite abundance were evaluated. • Generalised additive models were applied to analyse abundance data of the monogenean parasite. • A warm climate mediated by host defence mechanisms decreased parasite abundance. • Parasite abundance increased with the fish length, low temperature and cold months. One of the most intriguing questions in invasive biology is how an introduced species changes its population parameters in a new environment. Translocation of free-living species commonly results in co-introduction of their parasites. The current study focuses on the abundance pattern of the monogenean parasite Ligophorus llewellyni of the pacific so-iuy mullet, Planiliza haematocheila , across the native and introduced distribution ranges. We evaluated parasite release by the so-iuy mullet by comparing abundance patterns of L. llewellyni under effects of the host length, water temperature and month of the year in the Sea of Japan and the Sea of Azov. Generalised additive models applied to analysis of parasite abundance data showed that relationships between the mean number of L. llewellyni and the three tested independent variables were not linear. Our results suggest that the introduced host lost a large amount of parasite abundance due to the effect of warm climate in a new region, which is mediated by host defence mechanisms. The abundance of L. llewellyni rapidly rose in autumn, as fish activity and immune response decrease, reached the maximum in winter and began to fall in spring as a warm temperature facilitates the fish immune defence. The abundance of L. llewellyni showed an initial increase in response to fish growth and reached an asymptote. The response curves built for native and introduced regions reached an asymptote at different fish body lengths, reflecting the fish growth rate, which is higher in the introduced range of P. haematocheila. We found that the carried parasite species holds the same trend in relationships compared with its native area, between the mean number of monogeneans per host and independent variables increasing abundance with fish length, low temperature and cold months. Our results open new perspectives for future research on statistical modelling of parasite abundance across native and introduced distribution ranges in order to provide deeper insight into host-parasite interactions of invasive populations. [ABSTRACT FROM AUTHOR]

The diet composition and prey length of the Great Crested Grebe (Podiceps cristatus) and the Red-throated Diver (Gavia stellata) co-occurring in late autumn in two reservoirs was studied. Their diet was analyzed based on carcasses from incidental mortality of individuals in fishery gill net surveys in two different freshwater reservoirs (one deep, one shallow) in southern Poland during autumn migration (October - December). Five fish species were identified in the diet of the Great Crested Grebe and nine fish species were identified in the diet of the Red-throated Diver. The proportion of a particular fish species in diet was different between the studied bird species. The ruffe (Gymnocephalus cernua) was the most common prey in the diet of the Great Crested Grebe at both reservoirs. The diet of Red-throated Diver was dominated by roach (Rutilus rutilus) at the deep reservoir and the zander (Sander lucioperca) at the shallow one. The Red-throated Diver consumed larger fish than the Great Crested Grebe at both reservoirs. [ABSTRACT FROM AUTHOR]

In this study, the total lengths of the smaller mirror carp, that could not be caught, were estimated with the backcalculation methods using the scale and otolith lengths of larger fish. For this purpose, 50 fish samples were captured from Keban Dam Lake during October-November 2017 and October-December 2018. They were 4-9 in ages, 31.2-47.2 cm in total length and 442.5-1497.8 g in weight. The age of fish and the lengths of each age ring on scale and otolith were determined by using LAS V4.8 image analysis program attached to Leica S8APO microscope. The total lengths of fishes were calculated using Fraser-Lee and Dahl-Lea back-calculation equations for scale and otolith respectively. The mean total lengths calculated for all age groups from scale radius lengths and otolith lengths were L1:16.1, L2:21.3, L3:27.3, L4:30.5, L5:35.7, L6:36.7, L7:42.9, L8:45.3 ve L9: 45.9 cm and L1:14.2, L2:17.8, L3:22.8, L4:25.5, L5:33.1, L6:36.0, L7:41.0, L8:41.4 ve L9:44.0 cm respectively. In all age groups, total lengths of fish calculated from otolith lengths were found lower than total lengths of fish calculated from scale lengths. [ABSTRACT FROM AUTHOR]

An image can encode date, time, location and camera information as metadata and implicitly encodes species information and data on human activity, for example the size distribution of fish removals. Accurate length estimates can be made from images using a fiducial marker; however, their manual extraction is time‐consuming and estimates are inaccurate without control over the imaging system. This article presents a methodology which uses machine vision to estimate the total length (TL) of a fusiform fish (European sea bass).Three regional convolutional neural networks (R‐CNN) were trained from public images. Images of European sea bass were captured with a fiducial marker with three non‐specialist cameras. Images were undistorted using the intrinsic lens properties calculated for the camera in OpenCV; then TL was estimated using machine vision (MV) to detect both marker and subject. MV performance was evaluated for the three R‐CNNs under downsampling and rotation of the captured images.Each R‐CNN accurately predicted the location of fish in test images (mean intersection over union, 93%) and estimates of TL were accurate, with percent mean bias error (%MBE [95% CIs]) = 2.2% [2.0, 2.4]). Detections were robust to horizontal flipping and downsampling. TL estimates at absolute image rotations >20° became increasingly inaccurate but %MBE [95% CIs] was reduced to −0.1% [−0.2, 0.1] using machine learning to remove outliers and model bias.Machine vision can classify and derive measurements of species from images without specialist equipment. It is anticipated that ecological researchers and managers will make increasing use of MV where image data are collected (e.g. in remote electronic monitoring, virtual observations, wildlife surveys and morphometrics) and MV will be of particular utility where large volumes of image data are gathered. [ABSTRACT FROM AUTHOR]

Total lengths (LT) of 50 free‐swimming fish in a tank, silver carp Hypophthalmichthys molitrix and rainbow trout Oncorhynchus mykiss, were measured using a DIDSON (Dual‐frequency IDentification SONar) camera. Using Sound Metrics software, multiple measurements of each fish (LT, side aspect angle and distance from the camera) at different times were analysed by two experienced operators while a subset of data was analysed by two inexperienced operators. The main result showed high variability in intra‐fish LT measurements. The number of measurements required to minimise errors and to obtain robust fish measurements (true LT ± 3 cm) was estimated by a bootstrap method. Three to five measurements per fish were recommended for fish surveys in rivers. In this experimental study, aiming to reproduce river conditions, no evidence of fish position (side aspect angle and distance from the camera) effect was detected, but an operator effect (partially explained by training) was observed. General linear mixed models also showed that lengths of the smallest fish (LT < 57 cm) were overestimated and lengths of the largest fish (LT > 57 cm) were underestimated in comparison with their true lengths. In conclusion, we highlight that this technology, like any monitoring methods, returns imperfect observations. We advise DIDSON users to ensure that measurements are carried out correctly in order to draw accurate conclusion from this new technology. [ABSTRACT FROM AUTHOR]

In this study, the total lengths of Luciobarbus mystaceus species at previous ages were estimated from scale and otolith lengths by using back-calculation methods. For this purpose, 20 fish samples with 4-7 years in age, 37.1-47.4 cm in total length and 426.1-874.1 g in weight were obtained from a commercial fisherman in Keban Dam Lake. By using the backcalculation methods, the mean total length values for each ages calculated from scale lengths and otolith lengths were estimated as L1=7.7, L2=14.9, L3=21.4, L4=28.1, L5=30.3, L6=33.5, L7=35.7 cm and L1=7.5, L2=14.5, L3=19.2, L4=26.3, L5=29.6, L6=33.3, L7=33.9 cm respectively. The total lengths of fish calculated from scale and otolith measurements for all age groups were always determined smaller than observed total lengths of fish. There was a significant differences between calculated and observed lengths, but did not differ between total fish lengths calculated from scale and otolith measurements. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Both fishway types showed a similar good performance for barbel passage. • Fish length had a direct relationship on transit time. • Ecology and engineering should go hand in hand to improve mitigation efforts. Abstract When engineers and ecologists face a fishway design, many issues need to be considered, the type of fishway being the first and foremost. It is an especially complex issue in areas with species whose migratory and swimming behavior are as yet poorly known as Mediterranean barbels. The present study focuses on the fish passage of two of the most common types of technical fishways: Vertical Slot (VS), and Submerged Notch with Bottom Orifice (SNBO). Both types were studied and compared in terms of ascent ability (as the success rate and transit time) and motivation (as the proportion of attempts and attempt rate), with Iberian barbel (Luciobarbus bocagei) as the target species. Ascent ability in VS and SNBO were similar. More than 90% of fish ascended the fishways successfully and the median transit time to ascend a total water height of 2.25 m was less than 23 min. Fish length had an effect on ascent time, with the biggest ones being faster. Motivation was greater for VS, although not seeming to have a relevant influence in the passage. These results support the use of VS and SNBO in areas with Iberian barbel and provide new data of fishways performance helping ecologists and engineers with their decision making, mainly in Mediterranean areas with similar habitats and species. [ABSTRACT FROM AUTHOR]

In this study, the relationship between total length and otolith biometry of Barbus grypus Heckel, 1843 caught from Karakaya Dam Lake were investigated. For this purpose, total length of fishes and length, width and weight of otoliths in the both right and left inner ear of 88 fish samples were measured. Only right otoliths were used in this study. Because the difference between right and left otolith measurements was not statistically significant. The total lengths of the fish ranged between 388 and 862 mm. The length, width and weight of otoliths were 2.32-3.96 mm, 1.53-2.81 mm and 4.50-13.70 mg respectively. It was determined to be a highly positive correlation between total length of fish and otolith biometry. [ABSTRACT FROM AUTHOR]

Baited remote underwater stereo-video systems (stereo-BRUVs) are commonly used to sample fish assemblages across areas of differing fish densities with little consideration of how intraspecific and interspecific behaviours may influence estimates of abundance and body-size distribution. To investigate these potential biases, the current study compared the abundances and body-size distributions of seven target carnivorous species and six lower trophic level non-target species, across sites with high and low densities of large-bodied target species, using Stereo-BRUVs. Samples were collected inside and outside of an area closed to fishing at the Houtman Abrolhos Islands, Western Australia. Densities of large-bodied target species were found to be higher inside the closed fishery area, compared to similar areas outside. The presence of large-bodied target species did not appear to influence the body-size distribution of conspecifics, or the abundance and body-size distribution of small-bodied non-target species throughout the deployments. The abundance of large-bodied target species was found to peak earlier in deployments within the closed area than the areas open to fishing. This difference may be due to the higher relative density with the closed area, which may result in shorter arrival times as fish move towards the baited video, and/or to behavioural differences, as fish within the closed area may approach the baited video more readily. This potential behavioural difference between areas closed and open to fishing has important implications for duration of baited video sampling times, and we suggest that shorter deployments times (< 15 min) are less likely to bias abundance estimates of fishery target species. [ABSTRACT FROM AUTHOR]

An excessive and inappropriate handling of live fish is currently performed to obtain its size and weight. As an ameliorative attempt, a system named "IchthyoJHOL" was devised for the measurement of live specimens of fusiform fish species. The system holds the fish ventrally between supports and is mounted upon a scale. An image is captured on camera and processed with a digital measurement system. The system generates biometric data such as length, height and weight. This methodology creates a two-stage biometric process, the first being the capture of the images and the second their digital analysis, allowing for each stage to be carried out at distinct times and places. With this methodology, a reliability of over 96.8% is achieved, similar to that produced by the traditional system, but with a significant reduction in handling time and stress induced on the fish, allowing for large-scale biometric analysis. In addition, the library of fish images can be shared for posterior evaluation, redescription studies or a more extensive morphometric analysis. [ABSTRACT FROM AUTHOR]

In this study, the relationship between otolith biometry and total length of 48 females and 58 males belong to Capoeta trutta (Heckel, 1943) population of Keban Dam Lake (Elazığ) were examined between Nov ember 2011 and December 2012. After total length of fish sample were determined to the nearest ±1 mm, their sexes were determined by examining of gonads. Then right and left otoliths were removed and cleaned. Otolith weights were determined to the nearest ± 0.0001 g. The lengths and widths of otoliths were measured to the nearest ± 0.001 mm with a computer aided image analysis program. The thickness of otoliths were measure to the nearest ± 0.01 mm with a digital compass. The difference between right and le ft otolith data were not statistically significant (p>0.05). Therefore, only right sagittal otoliths were used for the determination of otolith biometry. The ages of fishes were determined. Mean values of otolith lengths, otolith widths, otolith weights and otolith thickness for male, female and all population were 3.06, 3.08, 3.07 mm; 2.24, 2.31, 2.27 mm; 6.94, 7.53, 7.20 and 1.12, 1.4, 1.13 mm respectively. According to correlation analyses results, moderate positive relationship in male, female and all population were found between otolith length-total length (r=0.33, r=0.46 and r=0.38), otolith width-total length (r=0.45, r=0.54 and r=0.49), otolith weight -total length (r=0.51, r=0.72 and r=0.65), otolith thickness-total length (r=0.48, r=0.55 and r=0.50) respectively. [ABSTRACT FROM AUTHOR]

Correlation between fish length, length and weight of otolith of sardine in the Southern waters of Iran still unknown. Therefore, because of commercial and ecological importance of Sardinella sindensis, relationships between fish length (total length), length and weight otolith was studied. In total, 123 Sind sardine were sampled by double –boat purse seiners from coastal waters of Jask from October 2010 to September 2011. Minimum and Maximum of length and weight of fishes were 7.8-19.19 cm and 4.63-59.11 g, respectively. Length and weight of otoliths were 1680.13-3339.45 mm and 0.0005-0.00261 g, respectively. Using t-test, no significantly differences were observed between left and right otolith (P>0.05). The results showed that there was relatively high correlation coefficient between fish length and otolith length (TL= 132.26 OL+ 730.17, r2=0.76), also between fish length and otolith weight (OW=0.00002TL1.6852 ,r2=0.75). For comparison between hypothetical (b) and calculated (b) in this study, t-test carried out, and result showed that the growth of fish and otolith is isometric (P>0.05).

The relationships between otolith dimensions and fish size (Fish total and fork lengths) for the teleost species, Rastrelliger kanagurta (Cuvier, 1817) collected from the vicinity of Muscat City at Oman Sea were examined and found to be linear. Otolith morphometric observations included length, weight and width were correlated with the total and fork lengths of the fish. Regression models relating each otolith morphometric parameter to the two fish lengths are provided. The significance of each parameter for estimating fish length was examined. The length, width and weight of otolith appeared to have the best discrimination for estimating total and fork length of fish as well as the easiest parameters to measure.

Regressions between fish length and otolith size are provided for 40 species from the north-eastern Atlantic Ocean and 142 species from the Mediterranean Sea. Regressions were also estimated at genus level. Most of the regressions ( c. 84%) explained a high percentage of the deviance (>75%). [ABSTRACT FROM AUTHOR]

Background: Sardines are the most important commercial fishes for Iran. However, information about biology and ecology of sind sardine in Persian Gulf and Oman Sea is scarce. Methods: In this study, relationship between fish length and otolith length, -width and -weight of Sardinella sindensis from Bandar Lengeh and Qeshm Island, Persian Gulf were analyzed. In total, 128 and 120 fishes collected from Commercial catches during March 2011- February 2012 in the Bandar Lengeh and Qeshm Island respectively. Results: There were no significant differences between left and right otolith (t-test, P > 0.05) or between males and females otoliths (ANCOVA, P > 0.05). For these reasons, only right otoliths were used for next analysis and data of both sexes were pooled. Relationships between fish length and otolith length, width and weight were described by linear regression models and high correlation was shown for all relationships. The highest correlation was between fish length and otolith length (Bandar Lengeh, R² = 0.8722; Qeshm Island, R² = 0.8661) and relationship between fish length and otolith width showed less correlation than other relationships (Bandar Lengeh, R² = 0.7355; Qeshm Island, R² = 0.7275). Conclusions: The result from this study shows that fish length and otolith growth have a positive relationship, so can be a useful tool to evaluate the growth of fish and fish stocks and finally fisheries management. [ABSTRACT FROM AUTHOR]

Fire in uplands and wetlands results in a release of nutrients and increased light in the burned area. However, fire effects on aquatic community dynamics are not well understood. We hypothesized that the addition of light and nutrients resulting from prescribed burns in wetlands increases periphyton biomass and supports increased standing stock of marsh fishes. In the oligotrophic Everglades of Florida, USA, we conducted a 2 × 2 factorial experiment using prescribed burns over standing water (increased nutrients and light), mowing with removal of above-water vegetation (no nutrient increase), and shade houses (no light) to test the prediction that fire effects would lead to more periphyton biomass and greater abundance and size of fish compared to other treatments. We observed increased periphyton percent cover and biomass per area in response to fire treatments. Fish abundance showed a short-term increase in burned plots. Fish length, mass, and condition factor did not respond consistently to treatments, though some species responded to specific treatments. Wildfires in dry marshes that may combust organic soils and vegetation may impact wetlands more than prescribed burns in flooded marshes. Our study suggests that wetland fires can affect aquatic animal and plant community structure, at least for short periods post-fire. [ABSTRACT FROM AUTHOR]

To manage fishery resources, defining the spatial distribution of biological populations is paramount. However, identification of populations can be controversial according to the methods used. The parasitofauna of the southern hake, Merluccius australis, in the Patagonian Fjord and Channel System of southern Chile, were analysed to determine if there was more than one ecological population. Samples were collected between spring 2004 and winter 2005 in three areas of the sea channels: in Chiloé (1); north of the Strait of Magellan (2); and south of the Strait of Magellan (3). In these areas, 219 hake specimens were collected, harbouring 26,071 parasites from 25 taxa. To determine whether any parasite taxon behaved as a biological tag, its abundance and prevalence was compared given body length, sex, and seasonality of the fish samples. The parasite communities among these areas were compared using GLM on the scores of the multivariate DECORANA analysis. The following criteria were used to select the taxa studied 1) taxa with a prevalence >5%, 2) parasites that accumulated through time (body length) in the fish, and 3) variability of their abundance among sites. The greatest variability in parasite abundance in these hakes was due to fish body length and sampling area, but not to fish sex and in general, not to seasonality to distinguish fish samples among the three areas. The digenean Aporocotyle australis characterized the samples from Chiloé that represented the smallest in body size. The nematode Anisakis sp. characterized the samples from south Magallanes that were the largest specimens. Fish from north Magallanes were similar in size to those of Chiloé but with smaller length range, and a transition of parasitofauna from Chiloé and south Magallanes samples. Statistical analyses of parasite taxa with a prevalence >5% and fish of all size classes (56–85 cm) showed significant differences in the parasitofauna abundance of southern hakes from the three sites. The analysis of fish length class 66–75 cm, the first maturity size, showed no significant differences among the Magallanes sites but both were different between the Chiloé sites. The parasitofauna of taxa with a prevalence >5% were useful as biological tags to discriminate between ecological stocks in the Magallanes areas compared to individual taxa but was time-consuming. Seven endoparasites and one ectoparasite are proposed as biological tags for future monitoring of ecological stocks in Chiloé and Magallanes. • The spatial definition of ecological populations of Merluccius australis is essential to manage this fishery resource. • The 16-taxa parasitofauna of the southern hake was used to discriminate ecological populations in the Chilean Patagonia. • Parasite community analysis distinguished two different ecological populations in both Magallanes areas. • Seven endoparasites and one ectoparasite are proposed as biological tags. [ABSTRACT FROM AUTHOR]

Natural fluctuations in the abundance and length of targeted fish are often disrupted by acute environmental changes and anthropogenic impacts, particularly fishing pressure. Long-term assessments of targeted fish populations inside and outside areas closed to fishing are often necessary to elucidate these effects, yet few of these studies extend over long time periods. We assessed trends in the abundance and length of six targeted fish species in areas open and closed to fishing on seven occasions spanning a 9-year period (2005-2010 and 2013) at the Houtman Abrolhos Islands, Western Australia. Shallow (8-12 m) and deep (22-26 m) coral-dominated reef sites were sampled across four geographically separated island groups using baited remote underwater stereo-video (stereo-BRUV). Between 2005 and 2010, populations of Lethrinus miniatus, Lethrinus nebulosus, Plectropomus leopardus, and Chrysophrys auratus became increasingly dominated by larger individuals, potentially indicative of an ageing population. Between 2010 and 2013, however, there was a significant increase in the proportion of smaller L. miniatus, L. nebulosus, and P. leopardus in both open and closed areas, reflecting increased recruitment perhaps due to changing environmental conditions associated with a marine heat wave anomaly. This recruitment pulse was not observed for the other species in this study ( Chr. auratus, Choerodon rubescens, and Glaucosoma hebraicum). Lethrinus miniatus, L. nebulosus, Chr. auratus, and P. leopardus were larger in closed areas relative to open areas; however, they were not more abundant. These complex responses to protection also varied across sampling years for certain species (e.g., P. leopardus). Monitoring changes over the long-term in areas open and closed to fishing provides a sound basis for separating environmental variability from that associated with fishing mortality, which is crucial for optimising fisheries management. [ABSTRACT FROM AUTHOR]

The relationships between size (length and width) of the lagenar (asteriscus) and the utricular (lapillus) otoliths and body length for five cyprinid fish species, freshwater bream Abramis brama, white bream Blicca bjoerkna, Prussian carp Carassius gibelio, brond-snout Chondrostoma regium, and rudd Scardinius erythrophthalmus, collected from Lake Ladik from November 2009 through October 2010, are presented. The right and left side measurements of otoliths were pooled in all cases except asteriscus length in Prussian carp. Nonlinear and linear functions provided the best fit for 80% and 20% of all species, respectively. All relationships were highly significant (P < 0.001, R² > 0.71) and the mean percent prediction errors were less than 10%. The results showed that reliable original size estimates of all species studied are obtainable from their otolith biometrics. The regressions from this study can be useful for investigators examining food habits of piscivorous fauna and sizes of these fishes in archaeological samples. [ABSTRACT FROM AUTHOR]