Fish Age Research Articles

Can amino acid racemization be utilized for fish age validation?

We investigated the relationship between aspartic acid d:l ratios and otolith-derived age estimates in Gulf of Mexico red snapper, Lutjanus campechanus (ages 1–26 years; R2 = 0.89) and Caribbean yellowtail snapper, Ocyurus chrysurus (ages 2–17 years; R2 = 0.84). The estimated racemization rate was 0.61 × 10−3 year−1 for red snapper and 1.28 × 10−3 year−1 for yellowtail snapper, reflecting temperature differences between study regions. Mean jackknifed error in ages predicted from aspartic acid d:l was 1.70 ± 0.39 years for red snapper and 1.57 ± 0.41 years for yellowtail snapper. Results suggest amino acid racemization may be an effective tool for direct age estimation and potentially age validation in fishes.

Age prediction by deep learning applied to Greenland halibut (Reinhardtius hippoglossoides) otolith images.

Otoliths (ear-stones) in the inner ears of vertebrates containing visible year zones are used extensively to determine fish age. Analysis of otoliths is a time-consuming and difficult task that requires the education of human experts. Human age estimates are inconsistent, as several readings by the same human expert might result in different ages assigned to the same otolith, in addition to an inherent bias between readers. To improve efficiency and resolve inconsistent results in the age reading from otolith images by human experts, an automated procedure based on convolutional neural networks (CNNs), a class of deep learning models suitable for image processing, is investigated. We applied CNNs that perform image regression to estimate the age of Greenland halibut (Reinhardtius hippoglossoides) with good results for individual ages as well as the overall age distribution, with an average CV of about 10% relative to the read ages by experts. In addition, the density distribution of predicted ages resembles the density distribution of the ground truth. By using k*l-fold cross-validation, we test all available samples, and we show that the results are rather sensitive to the choice of test set. Finally, we apply explanation techniques to analyze the decision process of deep learning models. In particular, we produce heatmaps indicating which input features that are the most important in the computation of predicted age.

Acute Copper Toxicity Displays a Nonmonotonic Relationship with Age Across the Medaka (Oryzias latipes) Life Span.

The ability of an organism to cope with environmental stressors varies across the life span because of developmental stage-specific responses and age-related functional declines. In the present study, we examined the effect of age on acute copper toxicity in Japanese medaka (Oryzias latipes). We first determined the median lethal concentration (LC50) at 96 h for embryos, 7-day-old fry, and 6-month-old medaka. Embryos were exposed to 0, 15, 30, 60, 125, 250, and 500 ppb CuSO4 through hatching. Fry were exposed to 0, 20, 50, 75, 100, 150, 250, and 500 ppb CuSO4 for 96 h. Adult fish were exposed to 0, 100, 150, 200, 250, and 300 ppb CuSO4 for 96 h. The 96-h LC50 was 804 ppb for embryos, 262 ppb for embryonically exposed larvae, 60.3 ppb for 7-day-old fry, and 226 ppb for adults. We then challenged cohorts of fish aged 2, 3, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, and 16 months with a 225-ppb CuSO4 exposure to determine the acute toxicity across the life span. The fish exhibited a bimodal tolerance to copper, with tolerance peaking in 2- and 3-month-old fish and again at 10 and 11 months of age. Our data demonstrate that copper sensitivity is dynamic throughout the medaka life span and may be influenced by trade-offs with reproduction. Environ Toxicol Chem 2022;41:2999-3006. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Evaluation of establishment and maintenance of primary cell cultures from several strains of common carp (Cyprinus carpio L.).

As a surrogate for the whole organism, primary cultures and cell lines serve as valuable tools for investigating exogenous and endogenous cytopathy. Studying cell responsiveness to diseases and contaminants is considered a less demanding and more readily accessible research approach that minimizes animal distress and provides more specific data. In the current work, the authors established primary cultures from several different organs and tissues of common carp (Cyprinus carpio L.) for subsequent use in other applications. They investigated the technical challenges in obtaining successful and durable carp-derived tissue cultures. The trials indicate that the type of tissue grown, carp strain and fish age impact equally upon culturing success, as do the cultivating conditions. Cells from gill epithelia, head and trunk kidneys, spleen, skin, gonads and ocular tissue were successfully established and maintained for further use in in-vitro testing. The primary cultures were, therefore, used to investigate and assess pathogens and pollutants emerging in carp's environment.

Persistent high hatchery recruitment despite advanced reoligotrophication and significant natural spawning in a whitefish

Many lakes of the pre-Alpine region suffered from severe eutrophication that affected the natural reproduction of whitefish (Coregonus spp.) and necessitated large-scale supportive breeding programs. With the advanced reoligotrophication, it is now important to evaluate the relevance of continued artificial breeding for population dynamics. We focused on a whitefish population of a lake that has reached phase III of the reoligotrophication, i.e., lake biomass production is declining since 2012 in response to low phosphorus concentrations. We show that most eggs are naturally spawned, the observed oxygen concentrations would again support embryo development at all depths, and ready-to-hatch embryos can indeed be found on spawning grounds. We marked all hatchery-produced eggs of the 2014 cohort with Alizarin red, stocked them as usual (at larval or early juvenile stages), and recaptured them over a period of five years. Fish were aged from yearly growth rings on scales, and otoliths were checked for marks. We found 90.3 % of the 2014 cohort to be hatchery-born. This ratio did not decline with fish age. We also determined juvenile growth of the cohorts 2012–2020 (based on the first annual ring on scales) and found that stocking intensity predicted juvenile growth (r2 = 0.67). This strong density dependence of individual growth suggests that stocking has largely determined cohort size over the first nine years of reoligotrophication phase III. We conclude that large areas of spawning grounds allow again for successful embryogenesis, that large quantities of eggs are naturally spawned, but that natural recruitment is significantly reduced by ecological or evolutionary factors, e.g., competition with hatchery-born fish, desynchronization of trophic interactions, or long-term effects of fishing- or hatchery-induced evolution.

Usefulness of Otolith Weight for EstimatingAge‐BasedLife History Metrics of Lake Trout

AbstractTo determine if otolith weight can be used to accurately and precisely estimate age‐based life history metrics of Lake TroutSalvelinus namaycushpopulations, we quantified relationships between Lake Trout otolith age and weight sampled from a wide geographic and size range of North American lakes. Separate nonlinear age–weight models for each of 22 surveys (each year within each area or lake) described 82.8% of variation in the relationship between otolith age and weight, whereas separate age–weight models for each of 13 lakes or areas within lakes (years combined) described only 0.4% less variation. Over all surveys, age increased at an average rate of 1.13 years per milligram increase in otolith weight and the otolith weight–age relationship was significantly nonlinear. Age of individual fish could not be estimated accurately from otolith weight alone, although bias of mean age estimated from mean otolith weight was small, whether using survey‐specific or general otolith age–weight relationships. Age at maturity and survival derived from indirect otolith age–weight relationships were estimated with less bias than growth parameters. We conclude that a general model for estimating Lake Trout age from otolith weight may be more useful for maturity and survival analyses that are less susceptible to estimation error of individual (often old) fish than for growth analysis that can be susceptible to estimation error of individual (often old) fish.

Challenges in fish aging: the role of otolith preparation technique and experience level in aging lake whitefish (Coregonus clupeaformis)

Lake whitefish ( Coregonus clupeaformis (Mitchill, 1818)) is an important commercial and recreational species in the Great Lakes. Precise age estimates are important for management, and two widely used techniques for otolith preparation are thin-section and crack-and-burn, which have not been compared for lake whitefish. Sagittal otoliths were collected from 92 lake whitefish in Green Bay and Lake Michigan and aged using thin-section and crack-and-burn techniques. Otoliths were aged independently by three individuals (two novices and one expert) to assess repeatability in estimated ages. Our investigation highlights the inherent difficulty of aging lake whitefish, where thin-section produced significantly older estimated ages (6–30 years) compared to crack-and-burn (5–26 years). Percent agreement of estimated ages between preparation techniques was low for all readers within ±0 years but increased when tolerance buffers were applied. Mean coefficient of variation values from both experience levels (>10.8%) exceeded the acceptable range reported in the literature (5%–7%); however, species longevity and nature of the structure must be considered when establishing target values. Variation in estimated ages is attributed to the experience level and interpretation of structural features. Species-specific training and establishing an objective framework to identify annuli will improve precision metrics.

Factors related to fish mercury concentrations in Iowa lakes.

Mercury contamination in aquatic ecosystems is a global concern due to the health risks of consuming contaminated fishes. Fish mercury concentrations are influenced by a range of biotic and abiotic factors that vary among regions, but these complex interactions are difficult to disentangle. We collected bluegill (Lepomis macrochirus), white and black crappie (Pomoxis annularis; P. nigromaculatus), largemouth bass (Micropterus salmoides), walleye (Sander vitreus), muskellunge (Esox masquinongy), and northern pike (E. lucius) from waterbodies throughout Iowa and analyzed them for mercury concentrations. We used land use, water chemistry, and fish characteristics to explain variation in mercury concentrations among and within systems. Mercury concentrations were generally low and undetectable (< 0.05mg/kg) in 43% of fish analyzed. Detected mercury concentrations were highest in largemouth bass, muskellunge, northern pike, and walleye, lowest in black and white crappie and bluegill, and positively related to fish length and age. Mean lake depth, pH, watershed area to lake area ratio, and percent of watershed as open water were positively related to fish mercury concentrations whereas lake area and percent of watershed as agriculture, developed, forested, and grassland were negatively related to mercury concentrations. Additionally, mercury concentrations were higher in shallow natural lakes compared to other lake types. Our results indicate fish mercury concentrations are lower in Iowa lakes compared to other regions. Models we developed in this study can be used to identify other waterbodies that may have elevated mercury concentrations that can guide fish mercury monitoring programs.

QUALITATIVE STRUCTURE OF SANDER MARINUS CUVIER, 1828 IN THE MANGISTAU COAST OF THE MIDDLE CASPIAN.

Predatory fish in aquatic ecosystems regulate the abundance of other species, which weakens the tension of competitive relations and stabilizes the community. Walleye refers to large pelagic predators, which, with a high number, effectively eat small and low-value commercial fish, performing a biomeliorative function in the fishing part of the community. At the same time, pike perch is in great demand, both on the foreign and domestic market. Its meat is considered a dietary product — its fat content is minimal. The nutritional value of walleye is very high — the protein content in it exceeds 18%. Zander meat contains 20 amino acids, 8 of which are irreplaceable (that is, they are not synthesized by the human body), and, in addition, contains a lot of minerals necessary for humans (phosphorus, potassium, iodine, molybdenum, manganese and others). It should also be noted that in Kazakhstan, only ordinary pike perch is caught and exported, the reserves of which are being depleted. Therefore, as an alternative, it is supposed to use a sea walleye.The biological resources of sea pike perch and other marine fish species of the Caspian Sea are not sufficiently exploited, since marine fisheries in our country are poorly developed, and the commercial population of these fish species allows increasing the catch in water areas under the jurisdiction of Kazakhstan. This paper describes the qualitative characteristics of sea zander caught in the research catches of the Mangistau coast of the Middle Caspian, as well as the degree of study in the Caspian Sea and other water bodies. The article describes the methodology for conducting a complete biological analysis of fish and presents statistical data processing. The paper gives a description of the following indicators: size-weight, age, sex ratio. Calculated fatness and determined the rate of size and weight growth in sea zander. Based on the results of these studies, a high correlation was found between age and weight, age and size of fish, and size and weight.

Abundance and Growth of the European Eels (Anguilla anguilla Linnaeus, 1758) in Small Estuarine Habitats from the Eastern English Channel

Abundance and growth of the European eel from six small northern French estuaries during their growth phase were examined to explore variations according to the local habitat characteristics. The length–weight relationships and growth models fitted to length-at-age back-calculated otolith growth increments were used to compare the growth. Higher abundances were observed in the smaller estuaries (2.4 to 10.5 ind. fyke nets 24 h−1). The eel length ranged from 215–924 mm with an age range of 4–21 years. There was no significant difference in fish eel lengths or age except in the Liane estuary where the individuals were larger. The length–weight relationships showed an isometric or positive allometric growth in most estuaries. The Gompertz growth models, which best fits the growth, showed no significant differences between estuaries except for female eels from the Liane and the Somme estuaries where the growth performance index was higher. The estimated annual growth rate varied from 2.7 to 115.0 mm·yr−1 for female and from 4.4 to 90.5 mm·yr−1 for male. The present study shows that eels in the six estuaries had CPUE and growth rates similar to those previously reported in larger habitats. These results reinforce the idea that small estuaries are important habitats that contribute significantly to the eel population and, therefore, play an essential role in conservation strategies for European eel.

Role of cytosolic carbonic anhydrase Ca17a in cardiorespiratory responses to CO2 in developing zebrafish (Danio rerio).

The sensing of environmental fluctuations and initiation of appropriate physiological responses is crucial to homeostasis. Neuroepithelial cells (NECs) in fishes are putative chemoreceptors, resembling mammalian Type I (glomus) cells, that respond in vitro to changes in O2, CO2, NH3, and pH. Cytosolic carbonic anhydrase (Ca17a) is thought to be involved in CO2 sensing owing to its presence in NECs. Zebrafish (Danio rerio) lacking functional Ca17a were generated via CRISPR/Cas9 technology and used to assess the role of Ca17a in initiating the cardiorespiratory responses to elevated CO2 (hypercapnia). Unfortunately, the homozygous knockout mutants (ca17a-/-) did not survive more than ∼12-14 days postfertilization (dpf), restricting experiments to early developmental stages (4-8 dpf). Changes in ventilation (fV) and cardiac (fH) frequency in response to hypercapnia (1% CO2) in wild-type (ca17a+/+), heterozygous (ca17a+/-) and ca17a-/- fish were used to investigate Ca17a-dependent CO2 sensing and downstream signaling. Wild-type fish exhibited hyperventilation during hypercapnia as indicated by an increase in fV. In the ca17a-/- fish, the hyperventilatory response was attenuated markedly but only at 8 dpf. Hypercapnic tachycardia was observed for all genotypes and did not appear to be influenced by the absence of Ca17a. Interestingly, ca17a-/- fish exhibited a significantly lower resting fH that became more pronounced as the fish aged. The decrease in resting fH was prevented ("rescued") when ca17a-/- embryos were injected with ca17a mRNA. Collectively, the results of this study support a role for Ca17a in promoting hyperventilation during hypercapnia in larval zebrafish and suggest a previously unrecognized role for Ca17a in determining resting heart rate.

792 Association of Dietary and Obstetric Factors with the Type of Gallstone

Abstract Aim Dietary and many other factors have been shown to increase the risk of gallstones, but their association with stone type is poorly understood. This study aims to assess the association of dietary and obstetric factors with the type of gallstone. Method 116 consecutive patients requiring cholecystectomy due to gallstone disease, admitted in our hospital, from January 2019 to December 2020 were included in this study. Demographic details, medical history, lifestyle and dietary habits, obstetric history and laboratory parameters were recorded using a data collection form developed by the researchers. Removed gallstones were classified as being cholesterol or pigment by gross visual inspection. Results Cholesterol gallstones were found in 76 (65.5%) and pigment stones in 40 (34.5%) of 116 total patients. Drug use was significantly higher in pigment stone group as compared to cholesterol group (p=0.002). Patients with cholesterol stones consumed significantly higher beef, fish and confectionery items than patients with pigment stones with a p-value of 0.043, 0.017 and 0.041, respectively. Parity was significantly higher in patients with pigment stones as compared to patients with cholesterol stones (p=0.023). A logistic regression model to assess the effect of beef, fish and confectionery item consumption and age at first pregnancy with the likelihood of having cholesterol gallstone was statistically significant (p=0.017) and showed that risk is higher in patients with age ≤ 20 years at first pregnancy [OR 6.89 (95% CI 1.24–38.15), p=0.027]. Conclusions This study concludes that diet and obstetric factors can influence the type of gallstone.

Age group DNA methylation differences in lemon sharks (Negaprion brevirostris): Implications for future age estimation tools.

Age information is often non‐existent for most shark populations due to a lack of measurable physiological and morphological traits that can be used to estimate age. Recently, epigenetic clocks have been found to accurately estimate age for mammals, birds, and fish. However, since these clocks rely, among other things, on the availability of reference genomes, their application is hampered in non‐traditional model organisms lacking such molecular resources. The technique known as Methyl‐Sensitive Amplified Polymorphism (MSAP) has emerged as a valid alternative for studying DNA methylation biomarkers when reference genome information is missing, and large numbers of samples need to be processed. Accordingly, the MSAP technique was used in the present study to characterize global DNA methylation patterns in lemon sharks from three different age groups (juveniles, subadults, and adults). The obtained results reveal that, while MSAP analyses lack enough resolution as a standalone approach to infer age in these organisms, the global DNA methylation patterns observed using this technique displayed significant differences between age groups. Overall, these results confer that DNA methylation does change with age in sharks like what has been seen for other vertebrates and that MSAP could be useful as part of an epigenetics pipeline to infer the broad range of ages found in large samples sizes.

Influence of hydrochemical factors on morphometric variability of Scardinius erythrophthalmus in a freshwater river system

Studying fish growth is a complex task because growth depends on many factors. The process of fish growth is influenced by ecological factors of the water environment. Each species of fish has growth characteristics and characteristic changes in this process as a result of the action of natural and anthropogenic factors. We investigated the morphometric features of Scardinius erythrophthalmus in the hydroecosystem conditions of the Horyn River. Fish were caught by amateur fishing methods during 2018–2021 in the section of the hydrographic system of the Horyn River within the Rivne Plateau, which is the northern part of the Volhynian Upland , namely the Horyn River and its tributaries – the Zamchysko River, the Ustia River, and the Stubelka River. The catches included fish aged from 0+ (one-year-olds) to 5+ (five-year-olds). Growth variability was studied for fish aged 1+ to 4+ because their numbers were sufficient for statistical evaluation. We noticed clear features of the morphometric variability of the fish. According to the coefficient of variation for the general populations of S. erythrophthalmus from different rivers, there was mostly significant variability of such growth characteristics as the largest and smallest fish body height, total length, Smith length and short body length of fish. We also noticed the similarity of the morphometric variability of fish of different ages for the Horyn River and Stubelka River and Zamchisko River and Ustia River. The analysis and evaluation of the surface water quality of these rivers was also similar. Thus, Horyn and Stubla districts had a transitional state from II to III quality class, and the Zamchysko River and Ustya River districts had a transitional state from III to IV quality class. We conducted a multivariate regression and it revealed statistical significance and a close correlation between the coefficients of variation of the growth characteristics of fish with the phosphate content in the water (with an average value of the weighting coefficients of 0.50 ± 0.06), nitrite nitrogen (0.39 ± 0.10) and nitrate nitrogen (0.84 ± 0.34). The calculation of the specific growth of fish by full length revealed that the intensity of growth is the highest between the first and second year of life of fish for small rivers (Zamchysko River, Ustya River, Stubelka River) and between the second and third year for the Horyn River. The results presented in the article are valuable and describe the local variation in the morphometric variability of S. erythrophthalmus. This expanded the understanding of the influence of ecological factors of the aquatic environment on the formation of growth characteristics of this species of fish. In the future, our research will continue and study the linear growth of natural fish populations against the background of changes in the ecological and hydrological conditions of the studied region

Bomb Radiocarbon, Otolith Daily Increments and Length Modes Validate Age Interpretations of Chilean Jack Mackerel (Trachurus murphyi)

Ages of Chilean jack mackerel (Trachurus murphyi) in the southern Pacific Ocean were validated using three methods: 1) daily microincrement readings in sagittal otoliths of young-of-the year (YOY) fish to validate the first annulus; 2) modal progression of strong year-classes (PSYC) to validate the first, second and third annuli, and 3) bomb radiocarbon analysis of otolith cores to validate the absolute age in older fish &amp;gt;38 cm fork length (FL). A Laird-Gompertz (LG) model was fitted to fork length (cm) at age (days) relationship in fish ranging from 3.4 to 25.0 cm FL and from 56 to 550 days in age. The LG model estimated a mean FL of 22 cm at the end of the first year of life, which was large compared with the mean FL estimated through conventional ageing in whole otoliths. The comparison between daily age with annual growth bands from whole otoliths, showed a false increment formed at 185 ± 34 days and a second translucent increment formed at 352 ± 79 days, corresponding to the first annulus for fish with the mean FL of 21.4 ± 1.8 cm. The PSYC coinciding with the recruits of 2008 (age 0), was tracked through three subsequent years with high accuracy, attaining 23, 27 and 30 cm FL in 2009, 2010 and 2011, respectively. These modes identified as age 1, age 2 and age 3 in the PSYC, matched to the mean length of fish with 2, 4 and 5 translucent increments in sagittal otoliths. Results from bomb radiocarbon analysis confirmed that most of the ages were correct, because the Δ14C content of adult otolith core matched the reference chronology. The absolute mean ages for the assayed otoliths, based on the comparison with the reference chronology, ranged from 7 to 13 years for sizes between 39 and 60 cm FL. The age validation for T. murphy as addressed in the current study provided crucial information for enhancing stock assessment output of this important transboundary commercial species.

Multivariate Nature of Fish Freshness Evaluation by Consumers.

The aim of the present study was to evaluate the sensory acceptability limit of refrigerated fish through a multivariate approach, involving classic physicochemical and bacteriological indicators and considering different consumer profiles. The results of the survival analysis demonstrated that, in general, consumers still considered the fish to be suitable for purchase (4.128 days of storage), despite being microbiologically unsuitable for consumption. However, the subsequent division of consumers into clusters indicated that women and individuals with high income and education levels tend to reject fish with few days of storage (3.650 days), mainly due to discoloration, despite still being microbiologically suitable for consumption. Thus, these segments present a safer behavior regarding the purchase of fresh fish. The influence of different frequencies of fish consumption and age of consumers on the assessment of fish freshness was not clarified. The responsibility for ensuring safe and healthy products at the point of sale must lie with the producers and distributors. However, improving consumers’ ability to make good choices when buying fresh fish would bring social and economic benefits related to public health and to the seafood industry, because it would enable them to make relevant claims and demand their rights.

Edwardsiella tarda- The Despised Threat to Nigerian Aquaculture and Human Health: A Review

Impediment to the aquaculture industry and consequently, impoverishment of the Nigerian populace can be attributed to several factors ranging from managemental to infectious or noninfectious. Despite the abundantly blessed land capacity and nourishment, the industry continues to face several losses. As part of the very important infectious agents known to cause high morbidity and mortality across several fish species is Edwardsiella tarda. E. tarda is directly associated with enteric septicemia in several fish species and ages. Infections caused by this bacterium is usually presented as gastrointestinal (gastroenteritis) and extra-intestinal (myonecrosis, bacteremia and septic arthritis) infections. E. tarda is an economic and public health threat because of its extensive impacts on the aquaculture industry as well as its ability to cause severe human infections such as diarrhea, gastroenteritis, typhoid-like illness, peritonitis with sepsis, cellulitis and meningitis. Furthermore, they are associated with the global antimicrobial resistance (AMR) in human and animal population. The threat posed by this bacterium have necessitated this current review on the overview of the risk factors and the presence of the organism in Nigeria. An elucidation into the bacterium, its epidemiology, threat to aquaculture industry and the global population are reviewed and the probable ways to control the presence of the organism are also discussed. Novel genetic engineering of the genes of the organism as a vital tool to drug and vaccine development are germane in this current age as a useful tool and strategy to have a world safe and in health. In conclusion, this review highlighted the necessary steps and approach to mitigate the bacterium and safe the Nigerian aquaculture from the emergence of a fatal infectious disease from fishes to human, as well as improvement in global trading.

Comparing growth and body condition of wild and hatchery M YY brook trout in streams and alpine lakes

Biologists have theorized that stocking YY males (created via in-hatchery hormonal sex-reversal and selective breeding; hereafter MYY fish) could be used to eradicate unwanted non-native vertebrate populations, but little is known about the fitness of MYY individuals once released into the wild. We compared growth and body condition of stocked hatchery-reared MYY brook trout (Salvelinus fontinalis Mitchell) to wild conspecifics in two streams and two alpine lakes. Maximum age for wild fish was age 6 at one stream and age 4 or 5 at the remaining waters, whereas for hatchery MYY fish, maximum age was age 5 at one stream and age 4 at the remaining waters. Total length ranged from 103 to 359 mm for wild brook trout and 115 to 353 mm for hatchery MYY brook trout. Growth rates and body condition of stocked MYY brook trout did not differ from wild fish in the same waters. Given that the success of MYY eradication programs is primarily contingent upon MYY individuals having fitness characteristics similar to wild conspecifics, our results provide further evidence that the stocking of hatchery-reared MYY fish may be a viable tool for eradicating unwanted non-native fish populations.

Levels, time trends, and distribution of dioxins and polychlorinated biphenyls in fishes from the Baltic Sea

Fish absorb dioxins from the environment through water and contact with sediments but the main source is food. These contaminants also enter the human body with food, including through the consumption of fish. This study presents the dioxin and polychlorinated biphenyl (PCB) concentrations in 145 samples of four fish species (herring, sprat, sea trout, salmon) caught in the southern Baltic Sea. The study results permit assessing whether the efforts made in recent years to reduce dioxin and PCB emissions into the environment have translated into decreases in concentrations of these pollutants in Baltic Sea fishes and whether these raw fish materials meet food law requirements. The safest fish species with regard to dioxins were designated, as were those of which consumption should be limited. The influence of fish age (length) and weight on dioxin and dioxin-like polychlorinated biphenyl (dl-PCB) concentrations was investigated. The correlation between fat content and dioxin concentration was determined. The Baltic Sea region and fishing ports from which the least contaminated fish come were also determined. The studies indicated that dioxin and PCB concentrationsin fishes from Polish fishing areas are currently lower than they were twenty years ago.

Information on forage fish ages from otoliths collected in avian stomach contents

Otolith analysis allows studying multiple aspects of fish biology, including age estimation; however, otoliths collected from avian stomach content have not been used to estimate the age of ingested fish. We evaluated the potential ability to estimate the age of Pacific sardine (Sardinops sagax) from otoliths collected from blue-footed booby (Sula nebouxii) stomach contents sampled in the Galapagos Islands. Blue-footed boobies were selected because they mostly forage close to their colony (&lt;100 m) and were, therefore, more likely to have almost intact otoliths. To estimate age, we employed three previously developed methods for otoliths. We then related these estimates to the fish's standard length and compared these relations statistically using the Akaike Information Criterion (AIC) to determine which method was most parsimonious. We collected 32 otoliths in relatively good condition, of which we aged 31 with the surface-reading method, 26 with the otolith weight method, and 29 with the posterior otolith length method. Average ages obtained with the otolith methods were 5.6 ± 1.7 yr (± standard deviation), 5.7 ± 2.0 yr, and 3.9 ± 1.5 yr, respectively. Estimates obtained with the otolith weight method had the highest correlation with standard length and the lowest AIC values of the three suggesting it was the best method for aging. Our results indicate that aging otoliths extracted from bird stomachs are possible; however, their use depends on the availability of previously developed methods and how digested the fish are when the birds return to the colony.