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Parasites play a key but overlooked role in the functioning of marine systems. Understanding the drivers of parasite infection in fish is thus crucial. Anisakis levels in the Atlantic horse mackerel Trachurus trachurus resulted from both biotic and environmental drivers. Ontogenic variation of the diet was the first driver of Anisakis level. The nonlinear pattern confirmed that the variation in parasitism was related to ontogenetic dietary shifts. The impact of depth on diet also explained the effect of depth on parasites. In deeper areas, fish only access pelagic prey, where Anisakis presence is high, consistent with the pelagic nature of the parasite. Finally, relative proportions of parasitic burden by tissue appeared to be driven by lipid content. In lipid-rich species like T. trachurus, Anisakis can find favorable conditions in the body cavity and in muscle and avoid the liver. Parasitism levels in fish are thus the result of patterns at play at different levels, and these factors should be better considered before being able to include parasites in an integrated vision of marine ecosystem functioning. Key words: Anisakis, fish parasites, environmental drivers, ontogenic shift, Introduction Parasites are nowadays recognized as key players in the functioning of marine ecosystems. They represent a major part of biodiversity, up to half of the living species for some [...]

Fish length back-calculation from hard structures (e.g., scales, otoliths, spines, etc.) is a commonly used method to reconstruct individual growth rates and sizes at age/stage in the absence of an intensive sampling-resampling timeseries. However, reliable estimates via these methods require the empirical validation of multiple assumptions about the growth of these hard structures. Here, we focus on reducing bias in scale-based back-calculations and validating proposed improvements using archived scales from a wild population of anadromous steelhead trout (Oncorhynchus mykiss). We first describe a series of back-calculation problems and propose solutions that can be integrated into common back-calculation methods. We then compare back-calculation accuracy, precision, and bias between proposed solutions and traditional forms of two backcalculation methods: Fraser-Lee and Body-Proportional. We discovered that the assumption that rapid growth begins immediately after juvenile steelhead pass downstream of the fish fence (300 m upstream of the ocean) was invalid and required a correction factor to prevent overestimating fish length by an average of 14%. The proposed modified methods we described performed better than traditional back-calculation methods. Overall, these findings can improve estimates of fish length from scale-based back-calculations and illustrate the importance of validating key assumptions. Key words: back-calculation, measurement error models, salmonids, scales, smolts Le retrocalcul de la longueur des poissons a partir de structures dures (p. ex. ecailles, otolites, epines) est une methode frequemment utilisee pour reconstituer les taux de croissance et les tailles selon l'age ou l'etape de vie d'individus en l'absence d'une serie chronologique d'echantillonnage repete intensif. Des estimations fiables obtenues par ces methodes requierent toutefois la validation empirique de differentes hypotheses concernant la croissance de ces structures dures. Nous nous penchons sur la reduction des biais dans les retrocalculs bases sur les ecailles et la validation d'ameliorations proposees en utilisant des ecailles d'archives issues d'une population sauvage de truites arc-en-ciel anadromes (Oncorhynchus mykiss). Nous decrivons d'abord une serie de problemes de retrocalcul et proposons des solutions pouvant etre integrees a des methodes de retrocalcul repandues. Nous comparons ensuite l'exactitude, la precision et les biais du retrocalcul des solutions proposees et de formes traditionnelles de deux methodes de retrocalcul, soit la methode de Fraser-Lee et la methode en proportion du corps. Nous relevons que l'hypothese voulant que la croissance rapide commence immediatement apres le passage des truites arc- enciel en aval du barrage (30 m en amont de l'ocean) est invalide et necessite un facteur de correction pour prevenir une surestimation de la longueur des poissons d'en moyenne 14 %. Les methodes modifiees proposees que nous decrivons donnent de meilleurs resultats que les methodes de retrocalcul traditionnelles. Globalement, ces constatations peuvent ameliorer les estimations de la longueur des poissons obtenues par retrocalcul base sur les ecailles et illustrent l'important de valider les hypotheses cles. [Traduit par la Redaction] Mots-cles : retrocalcul, modeles d'erreur de mesure, salmonides, ecailles, smolts, Introduction Understanding patterns and processes underlying somatic growth and body size is foundational to much of modern ecology and resource management--particularly for species that exhibit indeterminate and nonlinear somatic growth, [...]

Abstract Common aquaculture practices involve measuring fish biometrics at different growth stages, which is crucial for feeding regime management and for improving farmed fish welfare. Fish measurements are usually carried out manually on individual fish. However, this process is laborious, time-consuming, and stressful to the fish. Therefore, the development of fast, precise, low cost and indirect measurement would be of great interest to the aquaculture sector. In this study, we explore a promising way to take fish measurements in a non-invasive approach through computer vision. Images captured by a stereoscopic camera are used by Artificial Intelligence algorithms in conjunction with computer vision to automatically obtain an accurate estimation of the characteristics of fish, such as body length and weight. We describe the development of a computer vision system for automated recognition of body traits through image processing and linear models for the measurement of fish length and prediction of body weight. The measurements are obtained through a relatively low-cost prototype consisting of a smart buoy equipped with stereo cameras, tested in a commercial mariculture cage in the Mediterranean Sea. Our findings suggest that this method can successfully estimate fish biometric parameters, with a mean error of ± 1.15 cm.

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.

Calcified structures are valuable indicators being used in fisheries research for the estimation of fish ages or back-calculations of fish lengths. Such back-calculations typically assume constant proportional growth of fish and calcified structures independent of internal or environmental factors. We analyzed extensive data (1935–2020) of scale measurements from Norwegian spring-spawning herring. We applied linear quantile regressions to investigate the fish length – scale size relationship and environmental influences on individuals growing at different rates. We demonstrated that the fish length – scale size relationship varied over time and between cohorts, individuals of the same year-class. Parts of this variation can be attributed to changing environmental conditions. We identified a negative effect of stock total biomass and a positive effect of temperature on fish length when conditioned on scale size. The effect of stock total biomass varied considerably but the effect of temperature was similar between fish characterized by different growth rates. Our results are essential for long-term studies highlighting potential biases associated with environmental effects and different growth rates of individuals. These biases should be accounted for in growth history reconstructions and applications of the calcified structures as ecological indicators.

In this study, the relationships between otolith weight and dimensions with fish length were investigated in Neogobius species from Gobiidae. During this research, 149 specimens belong to three species, Neogobius pallasi, N. caspius and N. melanostomus, were collected using hand trawl net from Anzali, in the southwestern part of the Caspian Sea. After removing of otolith from specimens, otolith weight, length and height were recorded. The mean of otolith weight and dimensions were significantly different between three species; N. melanostomus had lower value in these parameters with respect to other species. In N. pallasi and N. caspius, otolith weight showed the highest correlations with fish length. In N. melanostomus, however, in addition to otolith weight, otolith length showed high correlation with fish length. According to the results of this study, probably, otolith weight and dimensions could be used as useful tools for determination of Neogobius species length in studies of trophic relationships in this region.

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.

Estimated parameters include the intercept HT ht , random year effects HT ht , and covariate effects HT ht . Like Faulkner et al. (2019), we modeled all interannual variation in freshwater and marine factors on survival as random year effects: HT ht . [Extracted from the article]

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).

Threatened or endangered salmon and steelhead originating in the Snake River basin must pass through a series of eight major hydroelectric dams during their seaward migration. Understanding the effects of specific dam passage routes on lifetime survival for these stocks is essential for successful management. Juvenile fish may pass these dams via three primary routes: (1) spillways, (2) turbines, or (3) juvenile bypass systems, which divert fish away from turbines and route them downstream. Bypass systems may expose fish to trauma, increased stress, or disease. However, numerous studies have indicated that direct survival through bypass systems is comparable to and often higher than that through spillways. Some researchers have suggested that the route of dam passage affects mortality in the estuary or ocean, but this is complicated by studies finding that fish size affects the route of passage. We tested whether passage through bypass systems was associated with the probability of adult return after accounting for fish length and other covariates for two species of concern. We also investigated the association between fish length and the probability of bypass at dams and how this relationship could lead to spurious conclusions regarding effects of bypass systems on survival if length is ignored. We found that (1) larger fish had lower bypass probabilities at six of seven dams; (2) larger fish had a higher probability of surviving to adulthood; (3) bypass history had little association with adult return after accounting for fish length; and (4) simulations indicated that spurious effects of bypass on survival may arise when no true bypass effect exists, especially in models without length. Our results suggest that after fish leave the hydropower system, bypass passage history has little effect on mortality. Our findings underscore the importance of accounting for fish size in studies of dam passage or survival. [ABSTRACT FROM AUTHOR]

Otoliths are widely used to estimate the age and growth of fishes and to identify fish species. This information plays a vital role in fisheries management and population dynamics studies. The information about fish length and otolith dimensions relationship of Upeneus vittatus is lacking from the Indian water. In this study, a total of 237 numbers of individuals were collected from October 2018 to March 2019 and left otolith was studied since there were no significant differences between right and left otoliths. The relationships between total length and otolith dimensions were estimated by linear regression analysis and found a strong positive correlation. The maximum correlation was found between fish length and otolith length for Mumbai populations (R² = 0.9342). In contrast, Kakinada populations had the maximum correlation between fish length and otolith width (R² = 0.8957), and Puri populations had the maximum correlation between fish length and otolith weight (R² = 0.9101). Present study found a strong positive correlation between fish length and otolith dimensions of U. vittatus. This finding provides new insights into the field and can be used for the growth study, fish population assessment, and fisheries management. [ABSTRACT FROM AUTHOR]