Age-0 Fish Research Articles

Increased mercury concentrations in walleye and yellow perch in lakes invaded by zebra mussels.

Zebra mussels (Dreissena polymorpha) are invasive species that alter ecosystems and food webs with the potential to affect aquatic mercury cycling and bioaccumulation in fishes, although the effect of zebra mussels on fish tissue mercury has not been tested in inland lakes. We assessed differences in fish tissue mercury concentrations and food webs in Minnesota lakes with and without zebra mussels while controlling for other lake and watershed characteristics. Mercury concentrations in adult walleye (Sander vitreus) and yellow perch (Perca flavescens) were 72 % and 157 % higher, respectively, in lakes containing zebra mussels compared to uninvaded lakes. Mercury in young of year (age-0) fish was also elevated, with mercury concentrations 97 % and 82 % higher in age-0 walleye and yellow perch, respectively, in zebra mussel lakes. Walleye mercury concentrations exceeded 0.22 ppm - a threshold triggering more restrictive human consumption advisories for sensitive populations - at a 23 % smaller size, and average-sized walleye (420 mm) exceeded this threshold at a rate of 77 % in invaded lakes, compared to 35 % in uninvaded lakes. Walleye and yellow perch relied more on littoral resources in lakes with zebra mussels but did not feed at meaningfully higher trophic levels. Increased fish tissue mercury in lakes invaded by zebra mussels have consequential implications for fisheries and human health.

Factors Influencing the Prevalence of Hyperpigmented Melanistic Lesions in Smallmouth Bass Micropterus dolomieu in the Susquehanna River Basin, Pennsylvania.

Hyperpigmented melanistic lesions (HPMLs) are a visual anomaly documented on the skin of smallmouth bass Micropterus dolomieu in the Susquehanna River Basin, Pennsylvania and in numerous other geographical locations. Currently, there is a lack of information on environmental and fish characteristics that may influence the prevalence of HPMLs associated with a recently described Adomavirus. The goal of this study was to understand potential drivers associated with HPMLs in socioeconomically and ecologically important riverine smallmouth bass populations. A total of 16,220 smallmouth bass were collected and examined for HPMLs between 2012 and 2022 in the Susquehanna River Basin. Overall, HPMLs were documented on 2.9% of fish collected. The interaction between temperature and fish size suggested differing relationships between shorter and longer fish with respect to temperature. Predicted probability of HPML prevalence ranged from 1.1% (95% CI = 0.3, 3.2) at 4°C to 0.01% (CI = 0.00, 0.04) at 26°C for an age-0 (125 mm) fish. In contrast, predicted probability of HPML prevalence ranged from 10.5% (95% CI = 5.8, 18.9) at 4°C to 0.8% (CI = 0.4, 1.5) at 26°C for an adult (322 mm) fish. Overall, HPMLs were more common in longer fish during cooler temperature periods which also corresponds to key life history periods for smallmouth bass (e.g., pre-spawn and overwintering) and could represent different exposure histories for juvenile and adult fish.

A method for estimating biomass of age-0 fish in case of protracted spawning leading to multiple larval cohorts in the population

We propose a new method for estimating the density and biomass of fish larvae and early juveniles when spawning is extended over time and the egg production in spawning groups varies widely with time. As a proof of concept, the method is applied to catch data for age–0 polar cod (Boreogadus saida), collected by the ichthyoplankton survey in the Kara Sea in 2019. The biomass among different size classes of age–0 fish was calculated based on the selectivity of a Bongo net with 500-μm mesh size. The age of larvae and juveniles in each group and average length at hatch (5.5 mm) were determined used for assessing average growth rate (0.18 mm/day) and hatching date for each age–0 fish assemblage. By fitting the population curve to the samples of age–0 polar cod collected in a small area sequentially over ten days, the instantaneous rate of natural mortality was estimated as ∼ 0.05 day-1. Changes in abundance and biomass over time were modeled by the Baranov's equation and power growth function. The average biomass for the time step of interest was calculated by projecting each cohort abundance to a selected point in time and taking a weighted average of all cohort biomasses.

Validity of winter sampling for estimation of salmonid abundance by electrofishing

Electrofishing removal sampling is a common method for abundance estimation of juvenile salmonids in streams and is usually performed during autumn. European guidelines specify that sampling should be conducted at water temperatures ≥ 5 °C, but studies investigating the validity of sampling below this threshold are lacking. We conducted electrofishing experiments during autumn and winter in three Norwegian rivers, comparing abundance estimation accuracy, rate of fish emigration from electrofishing sites, and mortality for juvenile Atlantic salmon Salmo salar and brown trout Salmo trutta. Abundance estimates were significantly more accurate during autumn than during winter, less accurate for age-0 fish than for older parr, and more accurate when the number of electrofishing passes was increased. By digging through the substrate after electrofishing, we found that a higher proportion of fish were uncatchable during winter than during autumn, and that age-0 fish were more likely than older fish to be uncatchable. For salmon older than age-0, both autumn and winter sampling consistently yielded relatively accurate abundance estimates. However, the rate of fish emigration from electrofishing sites was significantly higher during autumn than during winter and if block nets are not used, emigration during autumn sampling could cause severe underestimation of Atlantic salmon abundance. Fish mortality did not differ between autumn and winter sampling and was low for both species and all age groups. We recommend the use of block nets and conducting five electrofishing passes to reduce the likelihood of severe estimation error.

A mathematical model predicting the abundance and spatio-temporal dispersal of adfluvial salmonid (Salvelinus malma) fry in a stream

Models describing the spatial and temporal distributions of fishes are necessary for conservation and management of populations and their habitats. The early life stages of fishes are a particularly important period that can influence population dynamics and fisheries productivity. The fry of riverine migratory fish species are particularly influenced by downstream transport although relatively few models have been used to predict spatio-temporal abundance and dispersion of fry in combination with life history parameters in unperturbed habitats. We present a novel model predicting the downstream dispersal of age-0 adfluvial Dolly Varden in a spawning stream draining into Kronotskoye Lake basin, Kamchatka Peninsula, Russia. The model accounted for the number of and distance between known spawning grounds, diel activity, daily fish growth, and intra-specific diversity (i.e., morphotype) to describe how fry abundance changed at a specific stream location over the course of spring and summer. Data were collected using a trapnet monitored periodically during spring and summer to record changes in abundance, size (growth), and life history composition (‘nosed’ or ‘white’ morphotype) of fish between age-0 and -2. The experimental data were fitted to the model using a gradient descent optimization algorithm and a mean squared error loss function was used to verify how well experimental data fit to the theoretical model. The predicted abundance of age-0 fish was 18,831 with a mean dispersion rate of ∼36 m/day and a transit time between spawning area and stream mouth ranging 32–76 days. The catch was mainly comprised (81%) of the slower growing ‘nosed’ morphotype and exhibited variation in abundance over time and decreased considerably by the end of summer. Our comprehensive model will be useful to simulate the downstream dispersal of salmonid fishes whose early life stages inhabit riverine systems.

Age affects otolith shape in a coastal pelagic fish (Scomber colias Gmelin, 1789)

Otolith shape analysis is a common and efficient technique to study the population structure of fish species. This approach compares the overall otolith shape among individuals collected along the species´ distribution range. Otolith shape may change during ontogeny; thus, comparing otolith sample collections comprising multiple and variable age classes may lead to biased results. Therefore, it is crucial to test for possible effects of age on the otolith shape for a given species before interpreting potential differences in otolith collections. Here, we explored the effect of age on the otolith shape of a coastal pelagic fish species with a wide geographical distribution and fast growth rate, the Atlantic chub mackerel Scomber colias (Gmelin, 1789). This effect was tested across different years using different age assignment techniques (direct age reading and age back-calculation) and otolith shape descriptors (Elliptic Fourier and Discrete Wavelet). The results show that the age effect on otolith shape is most noticeable between age-1 and older fish, possibly due to rapid growth during the first year of life. Also, the age effect on otolith shape depended on the descriptor used, being more detected when using the Discrete Wavelet descriptor compared to Elliptic Fourier. Our results highlight the need to carefully examine age effects on otolith shape before conducting population structure analysis on mixed-age sample collections.

Nursery origin of yellowfin tuna in the western Atlantic Ocean: significance of Caribbean Sea and trans-Atlantic migrants

Natural geochemical markers in the otolith of yellowfin tuna (Thunnus albacares) were used to establish nursery-specific signatures for investigating the origin of fish captured in the western Atlantic Ocean (WAO). Two classes of chemical markers (trace elements, stable isotopes) were used to first establish nursery-specific signatures of age-0 yellowfin tuna from four primary production zones in the Atlantic Ocean: Gulf of Mexico, Caribbean Sea, Cape Verde, and Gulf of Guinea. Next, mixture and individual assignment methods were applied to predict the origin of sub-adult and adult yellowfin tuna from two regions in the WAO (Gulf of Mexico, Mid Atlantic Bight) by relating otolith core signatures (corresponding to age-0 period) to baseline signatures of age-0 fish from each nursery. Significant numbers of migrants from Caribbean Sea and eastern Atlantic Ocean (EAO) production zones (Gulf of Guinea, Cape Verde) were detected in the WAO, suggesting that fisheries in this region were subsidized by outside spawning/nursery areas. Contributions from local production (Gulf of Mexico) were also evident in samples from both WAO fisheries, but highly variable from year to year. High levels of mixing by yellowfin tuna from the different production zones and pronounced interannual trends in nursery-specific contribution rates in the WAO emphasize the complex and dynamic nature of this species’ stock structure and population connectivity. Given that geographic shifts in distribution across national or political boundaries leads to governance and management challenges, this study highlights the need for temporally resolved estimates of nursery origin to refine assessment models and promote the sustainable harvest of this species.

Spatiotemporal variations and influential factors affecting reproductive dynamics of Pacific saury in the Northwest Pacific during fishing season.

This study examined the spatial and monthly variations in reproductive dynamics of Pacific saury collected in the high sea (40°N-49°N, 149°E-168°E) of the northwestern Pacific during the fishing season of the Taiwanese stick-held dip-net fisheries (July-November) from 2018 to 2019. Generalized additive mixed-effects models (GAMMs) were applied to explore the relationship between the probability of maturing and spawning occurrence (PMOS ) and the explanatory variables (month, body length, sea-surface temperature [SST] as fixed effects, and fishing set as a random effect) for the age 0 and age 1 fish, respectively. In addition, the impact of the geographical difference in growth rates of age 0 fish, quantified as the radius of the otolith annual ring, on the PMOS of age 1 fish was explored in the GAMMs. Results showed that the mean values of the condition factor (CF) varied by months, and higher mean CFs were observed north of 45°N. However, the mean values of the gonado-somatic index did not show a clear spatiotemporal pattern. The spatial distribution of the ovarian maturation states revealed that the spawning ground of Pacific saury during July-November was broader than that previously known and had partly overlapped with the high-sea fishing ground. The best GAMM showed that the predicted PMOS of the age 0 fish were generally low (mean = 19%, standard deviation [SD] = 10%) and tended to increase with increasing body length. In contrast, the predicted PMOS were relatively higher (mean = 37%, SD = 10%) for the age 1 fish and increased with increasing SST and decreasing latitude. Two candidate GAMMs, which are equally supported as the best model (ΔAIC < 2), provide evidence that a higher growth rate of age 0 fish may result in higher reproductive activity in age 1 fish. This is one of few studies focusing on the reproductive dynamics of Pacific saury during the fishing season; current limitations, future directions, and conservation implications were discussed.

Dietary comparison of age-0 sturgeon (Scaphirhynchus sp.) between upper and lower Missouri River basins

Understanding potential limiting factors affecting population growth of the endangered pallid sturgeon, Scaphirhynchus albus, is important in the upper (UMOR) and lower Missouri River (LMOR) basins. The UMOR is upstream of several reservoirs and generally has more natural habitat features, whereas the LMOR is downstream of these reservoirs and has been channelized to support navigation. In both sections, pallid sturgeon recruitment to age-1 is a concern, but hypothesized for different reasons. One hypothesis in the LMOR centers on food limitation for age-0 fish, which is not considered an issue in the UMOR, but evaluating this hypothesis is challenging given the rarity of age-0 pallid sturgeon. As a result, the related, more abundant shovelnose sturgeon (S. platorhynchus) has been considered as a potential surrogate to assess food-related hypotheses. Thus, the purpose of our study was to compare diets of age-0 sturgeon captured in 2016 from three reaches in the LMOR (Copeland, Langdon, and Lexington) with individuals captured from a reach in the UMOR (Williston) during the same year to provide additional context regarding potential food limitation in the LMOR. Consumption percentage (prey weight in the gut as a percentage of body weight) was similar among all reaches, but diet composition was different for the most downstream reach in the LMOR. Age-0 sturgeon in the UMOR reach as well as the two upstream LMOR reaches primarily consumed Diptera larvae along with Ephemeroptera nymphs. In contrast, age-0 sturgeon in the most downstream LMOR reach (Lexington) almost exclusively consumed Diptera larvae. These results may provide information on relative differences in prey availability between Lexington and the other upstream reaches but the similarity in consumption percentage values across all reaches provide further evidence that age-0 sturgeon are not food limited in the LMOR.

Reduction in overwinter body condition and size of Pacific sand lance has implications for piscivorous predators during marine heatwaves

Acute anomalous ocean warming events, including marine heatwaves (MHWs), have significant effects on reproduction and survival of piscivorous seabirds. Additionally, MHWs have negative effects on seabird fish prey, exacerbating these consequences and resulting in population implications for seabirds. We evaluated the relative body condition of Pacific sand lance Ammodytes personatus, an important seabird forage species, in Haro Strait, a highly productive region of southern British Columbia, Canada. We compared body condition and length of fish cohorts that experienced the 2016 MHW year (MHW cohorts) with fish hatched during 3 subsequent post MHW years (2017-2019). Age-0 MHW cohorts had a seasonal decline in body condition in age-0 fish from 100% in the summer to 81% in the winter, while age-1 fish showed a decline from summer-fall highs of 93.5% to wintertime low of 79.5%. In comparison, post MHW cohorts had a winter body condition that was 2-4 times higher than their MHW cohorts. Similar to previous studies in Alaska during the MHW, age-1 fish failed to grow and reach the typical size that distinguishes them from age-0 fish. Poor sand lance condition and growth in winter may explain the ramifications of a warming ocean for top predators, including seabirds and Pacific salmon, which depend on these prey fish in Haro Strait. Our results support the idea that Haro Strait, which is influenced by estuarine circulation resulting in cooler temperatures than surrounding areas, serves as a climate refugium for sand lance populations in summer and provides buffering capacity to ocean climate warming events.

Condition, size, and winter duration affect winter survival probability of juvenile Atlantic cod Gadus morhua in a coastal subarctic ecosystem

Juvenile Atlantic cod Gadus morhua in coastal Newfoundland, Canada, settle in nearshore habitats in 3-6 pulsed events each year, from mid-summer to early winter, creating a broad size range of age-0 fish within each year-class, with potentially different survival trajectories entering their first winter. We hypothesized that early-arriving pulses, high autumn body condition, and low winter severity would contribute to high first-winter survival of age-0 cod. To test these hypotheses, we examined juvenile cod catch data, archived samples, and winter temperature records to determine the impact of winter duration, body condition, and settlement time on winter survival from 2001 to 2019. Settlement pulse, pre-winter condition, and winter duration had an interactive effect on survival. Fish condition did not vary across pulses within a given year-class, but we observed improved winter survival during long winters when body condition was high, with highest survival among the larger, early-arriving pulses of fish. Late-arriving pulses of fish were small-sized before winter onset, but these pulses unexpectedly survived better than pulses settling earlier in the season during short winters when body condition was high. However, all settlement pulses had a survival advantage when settlement occurred earlier on average (associated with warmer autumns), suggesting that increased growth and size within a pulse can also contribute to overwintering success. Our findings challenge some assumptions of overwintering ecology (e.g. ‘bigger is better’, low temperature stress) but illustrate the importance of cohort effects for overwintering survival in a sub-arctic marine ecosystem in a changing climate.

Pacific cod or tikhookeanskaya treska (Gadus macrocephalus) in the Chukchi Sea during recent warm years: Distribution by life stage and age-0 diet and condition

Many fish species have moved poleward with ocean warming, and species distribution shifts can occur because of adult fish movement, or juveniles can recruit to new areas. In the Bering Sea, recent studies document a dramatic northward shift in the distribution of Gadus macrocephalus (Pacific cod in English and tikhookeanskaya treska in Russian) during a period of ocean warming, but it is unknown whether the current northward distribution shift continues into the Chukchi Sea. Here, we use catch data from multiple gear types to present larval, age-0, and older Pacific cod distributions from before (2010 and 2012) and during (2017, 2018, and 2019) recent Chukchi Sea warming events. We also report on the habitat, diet, and condition of age-0 Pacific cod, which were present in the eastern Chukchi Sea in recent warm years (2017 and 2019), but were absent in a cold year (2012). We hypothesize that age-0 recruitment to the eastern Chukchi Sea is associated with recent warm temperatures and increased northward transport through the Bering Strait in the spring. Age-0 fish were present in both benthic and pelagic habitats and diets reflected prey resources at these capture locations. Age-1 Pacific cod were observed in the western Chukchi Sea in 2018 and 2019, indicating possible overwinter survival of age-0 fish, although there was little evidence that they survive and/or remain in the Chukchi Sea to age-2. Observed low lipid accumulation in age-0 Pacific cod from the Chukchi Sea suggests juvenile overwinter mortality may be relatively high compared to more boreal regions (e.g. Gulf of Alaska). Adult Pacific cod were also observed in the Chukchi Sea during 2018 and 2019. Although densities in the western Chukchi Sea were very low compared to the Bering Sea, the adults are the first known (to us) records from the Chukchi Sea. The increased presence of multiple age-classes of Pacific cod in the Chukchi Sea suggests poleward shifts in both nursery areas and adult summer habitat beyond the Bering Sea, but the quantity and quality (e.g. summer productivity and overwintering potential) of these habitats will require continued surveys.

Характеристика першого селекційного покоління антонінсько-зозуленецького внутрішньопородного типу українських порід коропа на 3 та 4 році життя

Purpose. To provide a comprehensive characterization of the first selective breeding generation of the Antoninsko-Zozulenetsky intrabreed type of Ukrainian carp breeds at the 3rd and 4th year of life based on piscicultural and biological parameters. Methodology. The material for the study were age-2+ and age-3+ Antoninsko-Zozulenetsky carps. The main piscicultutral and biological parameters were studied during spring valuation and autumn harvest according to generally accepted methods in fish farming. The external evaluation of the experimental groups was carried out according to the following parameters: body weight and length, body depth, body girth. Measurements were made with a centimeter tape with an accuracy of 1 mm. Individual weighing of fish was carried out on electronic commercial scales with an accuracy of 1 g. Based on the results of the measurements, following exterior parameters were analyzed and determined: girth index, body length to depth ratio, head index. Findings. The study showed that both age-2 and age-3 framed carp had a lower weight loss rate of 11.95 and 10.11%% compared to 12.89 and 12.73%% in the scaly form. The yield from wintering was within 88.6–89.8% of age-2 fish and 88.9–89.3% of age-3 fish. The average body weight gain age-2+ framed carp during the season was 1.3 kg, the scaly carp - 1.1 kg. On the fourth year of life, this parameter in scaly carp was 1.6 kg, framed carp - 1.5 kg. Survival rate during the growing season was higher than standard values and was on average 96.8% in age-2+ fish and 95.9% in age-3+ fish. According to external parameters, age-2+ framed carp had higher values ​​of the body length to depth ratio by 0.3, compared to their peers with a scaly cover. The advantage of this experimental group was also in terms of condition factor: 2.56 versus 2.26. On the other hand, among age-3+, scaly individuals had an advantage according to the body length to depth ratio. Age-3+ framed carp prevailed in terms of the condition factor. Originality. A comparative analysis of piscicultural and biological parameters of the replacement and brood stock of the first selection generation of the Antoninsko-Zozulenetsky intrabreed type of carp was carried out in the conditions of Ukraine for the first time. Practical value. The use of brood fish of a new inbred type with defined features of the genotype will allow obtaining new promising lines for industrial cultivation at different levels of intensification of aquaculture and in different climatic zones, as well as hybrids between geographically isolated populations. Key words: carp, selective breeding, intra­breed type, generation, exterior, weight, condition factor.

Four decades of climatic fluctuations and fish recruitment stability across a marine-freshwater gradient.

Investigating the effects of climatic variability on biological diversity, productivity, and stability is key to understanding possible futures for ecosystems under accelerating climate change. A critical question for estuarine ecosystems is, how does climatic variability influence juvenile recruitment of different fish species and life histories that use estuaries as nurseries? Here we examined spatiotemporal abundance trends and environmental responses of 18 fish species that frequently spend the juvenile stage rearing in the San Francisco Estuary, CA, USA. First, we constructed multivariate autoregressive state‐space models using age‐0 fish abundance, freshwater flow (flow), and sea surface temperature data (SST) collected over four decades. Next, we calculated coefficients of variation (CV) to assess portfolio effects (1) within and among species, life histories (anadromous, marine opportunist, or estuarine dependent), and the whole community; and (2) within and among regions of the estuary. We found that species abundances varied over space and time (increasing, decreasing, or dynamically stable); and in 83% of cases, in response to environmental conditions (wet/dry, cool/warm periods). Anadromous species responded strongly to flow in the upper estuary, marine opportunist species responded to flow and/or SST in the lower estuary, and estuarine dependent species had diverse responses across the estuary. Overall, the whole community when considered across the entire estuary had the lowest CV, and life histories and species provided strong biological insurance to the portfolio (2.4‐ to 3.5‐fold increases in stability, respectively). Spatial insurance also increased stability, although to a lesser extent (up to 1.6‐fold increases). Our study advances the notion that fish recruitment stability in estuaries is controlled by biocomplexity—life history diversity and spatiotemporal variation in the environment. However, intensified drought and marine heatwaves may increase the risk of multiple consecutive recruitment failures by synchronizing species dynamics and trajectories via Moran effects, potentially diminishing estuarine nursery function.

Age validation and growth in an exploited but poorly studied tropical fish species, the horse-eye jack (Caranx latus)

In this study, we investigated the size-at-age structure and growth of the horse-eye jack (Caranx latus), a highly mobile neritic species with significant commercial value in many parts of the tropical southwest Atlantic. For this, we combined size (standard length – SL) data and otolith readings from 282 juvenile and adult specimens of the species captured across a range of inshore (estuaries) and offshore habitats spread along the Brazilian coast between 2017 and 2019. Both otolith edge-type interpretation and marginal-increment width analysis suggested that annuli are deposited only once a year for C. latus in this part of the world, the opaque band being formed between May and August. The growth parameters estimated by the growth model that fitted best our size-at-age data (von Bertalanffy) were 782.37 mm for Linf, 0.179 for k and − 0.436 years for t0. Interestingly, fish ages differed between local inshore and offshore habitats: 91.8% of the individuals captured in the estuaries (36–223 mm SL) were age-0 fish, while all age groups (0–13 years) were found in the offshore marine area, where sizes ranged from 155 to 760 mm SL. Growth is apparently the fastest in the first year of life, allowing to reach up to 22.75% of the local maximum size expected for the species at one year. These results can inform fishery and ecosystem management strategies in Brazil but also elsewhere, as the present study provides the first assessment of C. latus growth in the South-Western Atlantic based on detailed size-at-age data for most life stages and lifetime habitats.

Характеристика рибницько-біологічних показників дволіток коропа, відтворених із застосуванням методів кріоконсервування статевих продуктів

Purpose. To create stocks of age-1 and 1+ carp produced with the use of defrosted and native sperm and provide the comprehensive characteristics of their quantitative and qualitative parameters. Methodology. The material for the study were age-1 and 1+ Nyvky scaly and non-scaly carp. Main quantitative and qualitative parameters were studied during spring assessment and autumn harvest using conventional aquaculture methods. Stocking density of age-0+ fish for wintering was 10 thousand kg/ha, age-1 fish – 1 thousand fish/ha. The exterior assessment of multiple age groups was carried out using following parameters: body weight and length, body depth, body circumference. Measurements were done using a measuring tape with a precision of 1 mm. Fish were weighed individually on electronic balances with a precision of 1 g. Following main exterior indices were determined and analyzed: circumference index, body length to depth ratio, head index. Findings. The study showed that age-1 fish produced from defrosted sperm had 0.25 and 4.5% higher survivability during wintering with the prevalence of non-scaly carp, however they were characterized by higher weight loss: 1.13% for scaly carp and 1.65% for non-scaly carp. Age-1+ fish produced from defrosted sperm prevailed over their age-0+ by weight by 2.69% for scaly carp and by 7.34% for non-scaly carp. However, fish of the experimental group were characterized by lower survivability by 1.0% and 3.25% compared to the control group. Fish productivity parameters during the study period varied from 810.7 to 1056.0 kg/ha. Originality. For the first time in Ukraine, a comparative analysis of quantitative and qualitative parameters of age-1 and 1+ carp produced with the use of defrosted and native sperm was performed. Practical value. Use of the method of cryopreservation of sperm obtained from brood fish with desired peculiarities of genotype allows improving creation of highly productive stocks using methods of individual selection, getting highly productive crosses as well as hybrids between geographically isolated populations. Key words: carp, defrosted sperm, age-1 fish, age-1+ fish.

Reproductive ecology and adaptive host choice correlated with body size in an autumn-spawning bitterling Acheilognathus typus.

The life history and reproductive ecology of an autumn-spawning bitterling Acheilognathus typus were studied under natural and experimental conditions. In the study pond, the embryos of A. typus emerged from mussels in May and grew rapidly until August, whereas overwintered age-1 fish grew slowly. Adult A. typus in the pond was smaller (32-47 mm in standard length) than they were in other habitats and mainly spawned in smaller mussels. The number of A. typus embryos in mussels was negatively correlated with the shell length of the mussel, and a lower number of embryos were observed in larger mussels (over 110 mm in shell length). In the mussel size-choice experiment conducted in an enclosure, smaller A. typus selected smaller mussels, and larger A. typus selected larger mussels for spawning. In some cases, smaller A. typus spawned in larger mussels and the number of spawned eggs ejected increased by over four times compared with other cases. These results of the enclosure experiment explained the lower number of embryos in larger mussels in the study pond. In addition, reproductive traits such as ovipositor length and the number of ovulated eggs of female A. typus, which are considered to contribute to their size-dependent host utilization, were positively correlated with their standard length. Because A. typus is geologically or seasonally isolated from other bitterling species, this size-dependent host utilization contributes to a reduction in intraspecies rather than interspecies competition.

Resource partitioning may limit interspecific competition among Arctic fish species during early life

Arctic cod (Boreogadus saida) strongly dominates the ichthyoplankton assemblages of High Arctic seas, hence competition with other native species seldom has been studied. Yet, interspecific competition could negatively impact the survival of early life stages of fishes in Arctic areas where higher diversity prevails. We surveyed the ichthyoplankton community of the Greenland Sea, in August–September 2017. Gadids (mostly Arctic cod, with a low number of ice cod Arctogadus glacialis) and non-gadids (bigeye sculpin Triglops nybelini and gelatinous snailfish Liparis fabricii) co-dominated age-0 fish assemblages. Here, we document their diet, prey selectivity, horizontal and vertical distributions as well as that of their prey to assess resource partitioning and the potential for interspecific competition. All fish species occupied the top 30 m of the water column, but Arctic cod occurred in highest abundances over the continental slope, whereas other species distributed almost exclusively over the continental shelf. A particle track analysis suggests that Arctic cod larvae could have hatched in the open waters of the Northeast Water Polynya, drifted with the East Greenland Current, and benefited from the high secondary production associated with these oceanographic features. The diet of gadids did not overlap significantly with the diet of non-gadids, but strong selectivity for Pseudocalanus spp. and Calanus spp. copepodites among the larvae suggests potential competition for these key prey items, although limited by size partitioning of the prey. We thus conclude that interspecific competition among early life stages of Arctic fishes is limited for now. However, changing conditions and the northward range expansion of boreal species following climate change could increase competition and, in turn, negatively affect the recruitment of Arctic ichthyoplankton.

Foraging ecology of nearshore fishes in the Gulf of Alaska

The survival of juvenile marine fishes, which support commercial fisheries and provide a prey resource, is often dependent on conditions in protective and nearshore habitats. We examined the trophic interactions of several juvenile fishes in the nearshore Gulf of Alaska (GOA) including Pacific cod (Gadus microcephalus), saffron cod (Eleginus gracillis), walleye pollock (Gadus chalcogrammus), Pacific sand lance (Ammodytes hexapterus), Pacific herring (Clupea pallasii), rockfish (Sebastes spp.) and greenlings (Hexagrammos spp.). We used fatty acid (FA) and stable isotope (SI) markers to evaluate foraging ecology and the potential for competition among age-0 fish species in broad east (134°W – 136°W) and west (149°W – 153°W) regions of the GOA. Sampling efforts were greater in the west GOA, so many of our findings were focused in that region. In the west GOA, FA and SI markers indicated that Pacific cod and saffron cod usually shared similar diets, potentially leading to competition for resources. Also in the west GOA, we found evidence that Pacific cod and walleye pollock both relied to similar extents on calanoid copepods during summer. Juvenile sand lance and herring were much smaller than the other species and had diets that contrasted with all other species. In both the east and west GOA, rockfish were present in two distinct size classes with the smaller size feeding at a lower trophic level than all other fish species in the study. The smaller rockfish likely consumed mainly calanoid copepods. Throughout the east and west GOA, greenling and rockfish typically consumed prey with a very different lipid source than the other juvenile fish. In addition, we noted few consistencies in FA and SI markers between the east and west, except in rockfish diets. Overall, we found a complex relationship within the nearshore fish communities in the east and west GOA that showed substantial variation across bays, seasons and subareas.

Assessing habitat for lake sturgeon (Acipenser fulvescens) reintroduction to the Maumee River, Ohio using habitat suitability index models

Lake sturgeon (Acipenser fulvescens) were a candidate for reintroduction in the Maumee River, Ohio, where they were historically abundant, but are now functionally extirpated. Our objective was to determine if current habitat quality and quantity could support reintroduction efforts. We developed a spatially explicit habitat suitability index model for two lake sturgeon life stages: spawning adult and age-0 fish. To estimate habitat quality, substrate, water depth, and water velocity were assessed and integrated into suitability index values to delineate good, moderate, and poor areas for each life stage. Each habitat characteristic was mapped and combined to provide an overall assessment of habitat suitability, quantity, and location. Model results indicated 208 ha (10.2% of all habitat) of good adult spawning habitat (e.g., coarse substrates, depths between 0.3 and 8 m, and velocity between 0.5 and 1 m/s) and 529 ha (28.2% of all habitat) of good age-0 habitat (e.g., fine substrates, depths between 0.2 and 6 m, and velocity between 0.1 and 0.7 m/s). Good age-0 habitat was located mostly downstream of good spawning habitat, which will provide nursery areas for age-0 fish after hatch. Our models suggested habitat is not limiting for lake sturgeon and efforts to reintroduce this species into the Maumee River, and for the first time in the Lake Erie basin, were supported. The results of this work supported reintroduction efforts that began in 2018.