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The oxygen environment around buried sandeels (Ammodytes tobianus) was monitored by planar optodes. The oxygen penetration depth at the sediment interface was only a few mm. Thus fish, typically buried at 1-4 cm depth, were generally in anoxic sediment. However, they induced an advective transport through the permeable interstice and formed an inverted cone of porewater with 93% air saturation in front of the mouth. From dye experiments the mean ventilatory flow rate was estimated at 0.26±0.02 ml min-1 (86.9±7.3 ml min-1 kg-1) (N=3). Expelled water from the gills induced a 1 cm circular plume with <15% air saturation around the gills. During this quasi-steady ventilation mode, fish extracted 86.2±4.8% (N=7) of the oxygen from the inspired water. However, 13% of the investigated fish (2 of 15) occasionally wriggled their bodies and thereby transported almost fully air-saturated water down along the body, referred to as 'plume ventilation'. Yet, within ~30 min the oxic plume was replenished by oxygen-depleted water from the gills. The potential for cutaneous respiration by the buried fish was thus of no quantitative importance. Calculations derived by three independent methods (each with N=3) revealed that the oxygen uptake of sandeel buried for 6-7 h was 40-50% of previous estimates on resting respirometry of non-buried fish, indicating lower O2 requirements during burial on a diurnal timescale. Buried fish exposed to decreasing oxygen tensions gradually approached the sediment surface, but remained in the sediment until the inspired water reached 5-10% air saturation. [ABSTRACT FROM AUTHOR]

• Response to simulated predatory attack was used to determine round goby as bold or shy. • Bold fish pay the costs of higher resting metabolic rate and smaller size-at-age than shy fish. • Metabolic underpinning of personality results in reduced growth in bold fish. • Bold fish at the invasion front may compensate by increased access to food. Differences between individuals in behavioral type (i.e. animal personality) are ecologically and evolutionarily important because they can have significant effects on fitness components such as growth and predation risk. In the present study we are used the invasive round goby (Neogobius melanostomus) from an established population in controlled experiments to examine the relationships among personality, metabolic performance, and growth rate (inferred as size-at-age). Boldness was measured as the time to return to normal behavior after a simulated predator attack, where fish with shorter freezing times were categorized as "bold" and fish with longer times were categorized as "shy." We show that bold fish have significantly higher standard metabolic rate (SMR) than their shy conspecifics, whereas there was no difference between personality types in their maximum metabolic rate (MMR) or aerobic scope (AS). Bold fish furthermore had a smaller size-at-age as compared to shy fish. Together this provides evidence of a metabolic underpinning of personality where the high-SMR bold fish require more resources to sustain basic life functions than their low-SMR shy conspecifics, indicating that bold round goby from established populations with high densities (and high competition for food) pay a price of reduced growth rate. [ABSTRACT FROM AUTHOR]

The round goby (Neogobius melanostomus ; Pallas, 1814) is one of the most widespread invasive fish species. It originates from the Black Sea and the Sea of Azov but has un-intentionally been introduced to fresh and brackish water bodies on both sides of the Atlantic. Small-scale fishermen catch large amounts of the invasive round goby as the species continues to spread and populate new areas of the Baltic Sea. We were concerned with the possibilities for a "use and reduce" solution to the round goby invasion. However, to capture the interest of restaurants, supermarkets, and distributers, more information about seasonality in product supply and nutritional quality is needed. We therefore studied a round goby bycatch fishery in the Western Baltic Sea (Denmark) and describe the seasonal dynamics in catch rates, size distribution, condition factor, lipid and protein content, fatty acid profile, and meat texture. We found that while the catch rates peaked in spring, lipid content and meat texture improved significantly, later in the year. Protein content also peaked in late summer and fall, but it was only marginally higher compared to spring. We compare the results to relevant species and conclude that round goby is a relatively lean fish all year (only slightly fatter than for example cod). The firmness of the meat in fall, resembles farmed trout and it has a highly favorable fatty acid composition, reflected by a low n-6 to n-3 ratio. The main bottleneck related to the introduction of round goby to the consumer market is likely going to be the small size. [ABSTRACT FROM AUTHOR]

A quantity of studies have documented how greater condition and older age of individual fish enhances reproductive success via a variety of processes from egg production to larval survival. If these relations translate into relationships between stock demography and recruitment, maintaining a "healthy" age composition may be a key step towards ensuring stock productivity. We examined the correlation between indicators of the age and size composition and the residual-variation from the stock-recruitment relationship (i.e. the variation not explained by the spawning stock biomass) in eleven commercially exploited fish stocks in the North Sea. We also analyzed to what extent spawner age and size composition responded to variations in fishing mortality. Before detrending to accommodate any temporal patterns, recruitment residuals correlated negatively with the relative age composition in all eleven stocks (plaice, whiting, and saithe being significant). However, after detrending the recruitment residuals, the correlations weakened and only nine out of eleven stocks correlated negatively. Lastly, we also conducted a delay difference analysis, which yielded a more or less even distribution between negative and positive correlations, and in addition two stocks (cod and Norway pout) came out showing significant positive correlations between recruitment residuals and age composition. In contrast, eight of the eleven stocks showed positive correlations between spawner weight and recruitment residuals and correlations were significant for plaice, cod, and saithe. After detrending the data, the significant correlations disappeared, but the overall tendency towards positive correlations between spawner weight and recruitment residuals prevailed. Overall, these results suggest that fish condition is more likely to show positive relationships with recruitment success than age composition. Lastly, it was found that the majority of stocks showed a strong link between fishing mortality and the two indicators of age composition, and when looking across stocks, the age composition appears to have returned to the same level as in the 1960 s. Conversely, spawner weight at age have not recovered, and considering the indications of a positive link between spawner weight and recruitment, recruitment success of the North Sea stocks may remain low in spite of the apparently successful rebuilding of the age composition. • A large proportion of old fish coincided with increased recruitment in Atlantic cod and Norway pout. • Individual weight of old fish in the spawning stock was often positively correlated with recruitment. • As expected, the age composition responded directly to changes in fishing pressure. • There was a general declining trend over time in the individual weight of fish in the spawning stock. [ABSTRACT FROM AUTHOR]

This study examines the sediment preferences of small sandeel (Ammodytes tobianus), an elongated forage fish common in marine and brackish environments of northern Europe. Sandeel have a high fidelity for sandy habitats and spend much of their lives buried, as an important part of both their diel behavioural cycles and overwintering behaviour. A series of independent choice laboratory assays were conducted using wild-caught schools of small sandeel, to: (1) determine their preferred substrate composition for burial; (2) identify the upper limits of sediment grain-sizes that may be utilised for burial, and; (3) investigate the effects of light intensity on burial behaviour. Initial experiments found a clear preference for burial within sediments composed of coarse sand and fine gravel (0.5–4.0 mm) but showed at least some utilisation of both coarser and finer sediment compositions. In further trials, burial was found to be almost entirely eliminated in sediments that contained significant gravel components >4.0 mm. Light manipulation experiments also showed that light intensity was an important factor that influences their choice of burial area. This study is the first to experimentally investigate the sediment preferences and grain-size tolerance limits of small sandeel. These results specifically highlight how subtle differences in both sediment composition and light may influence the habitat usage of small sandeel, which may be valuable for understanding their distribution in the wild and to inform future management and conservation for the species. • Investigated sediment preferences for small sandeel (Ammodytes tobianus). • Preferred substrate is coarse sand and fine gravel, but avoidance are observed when exposed to larger gravels of pebbles. • Initial findings of light gradients that influence sandeel burial behaviour are reported. • Results provide insights for understanding sandeel behaviour, ecology, and distribution in the wild. • A multinomial modelling approach is introduced to enhance data interpretation and address uncertainties for experimental studies. [ABSTRACT FROM AUTHOR]

Passive integrated transponder (PIT) tags are commonly used to assess fish movement for use in fisheries management. Here, we investigated physiological and behavioral effects of tagging on sandeels ( Ammodytes tobianus) using PIT tags constituting 2.1 ± 0.9% of their body weight. Swimming stamina ( RSS ), calculated as time spent swimming against the current relative to total swimming time, and tail beat frequency were compared between tagged and untagged fish as was blood hematocrit levels at 7, 14, and 42 d post-tagging. Survival and tag retention were also documented at 14, 42, and 84 d (via x-rays and dissections). RSS was not different between tagged and untagged fish with means (± SD) of 60 ± 9% and 61 ± 12%. Tail beat frequency was not different between tagged and untagged fish at 2.8 ± 0.3 and 3.0 ± 0.4 beats s −1 for tagged and untagged fish, respectively. Likewise, hematocrit was not affected by tagging and levels were between 21–26% for both groups. Survival rates were high and did not differ between groups (96% for tagged and 99% untagged fish). Tag retention was 100%. X-rays and dissections did not reveal any signs of tag movement at 14–84 d, and there was no difference between relative positions of the tags. None of the tags were encapsulated in the body cavity after 14 d, whereas 40 and 56% of the tags were encapsulated in a thin tissue membrane between the intestine and kidney after 42 and 84 d, respectively. After 14 d all incisions had healed with only minor or no signs of the tag insertion site. Collectively, these data provide substantial evidence for the possibility of conducting large-scale tagging studies on this species in the field. [ABSTRACT FROM AUTHOR]

The effects of pelagic trawling on the health and welfare of Atlantic herring (Clupea harengus L.) were investigated on a refrigerated seawater vessel operating in the North Sea. A total of 495 Atlantic herring (Clupea harengus L.) were sampled during five hauls from two fishing trips in September 2021 and 2022. For assessments of consciousness and mortality, a Reflex Action Mortality Predictor test (i.e. RAMP-test) was used on herring collected following trawling and pumping. Inspections for external and internal damage or wounds were performed via morphological welfare indicators and analyses of photos and radiographs. In addition, blood samples were taken and analysed for haematological indicators of stress. Following trawling and pumping, only 5% of the investigated herring showed signs of external wounds associated with the morphological indicators of welfare, and no internal damage was observed in the radiographic inspections. However, 96% of the assessed herring scored 0 on all three reflexes included in the RAMP-test and were therefore judged dead. On average, herring lost 95% of their scales, while 95% of herring had a very high degree of ruptured red blood cells (i.e. haemolysis). Extensive scale loss results in a deterioration of the skin's protective barrier function, which in turn impairs the osmoregulatory capacity of the herring. This was evident by elevated levels of plasma osmolality and circulating chloride concentrations, which could also likely explain the high occurrence of haemolysis in captured herring. Extended trawling time and larger catch size proved to be two important factors to consider, as the former led to increased plasma levels of osmolality, whereas the latter was associated with elevated plasma levels of lactate and cortisol. In conclusion, the high mortality appears to be influenced by a combination of factors such as severe stress, loss of osmoregulatory ability, crowding density within the trawl, and extended trawling times. This study provides important information on the welfare of wild Atlantic herring caught using pelagic trawls and highlights areas where improvements can be made to safeguard the welfare of fish captured in pelagic fisheries in the future., (© 2024. The Author(s).)

The round goby (Neogobius melanostomus) is a fish native to the Ponto-Caspian region that is highly invasive through freshwater and brackish habitats in northern Europe and North America. Individual behavioural variation appears to be an important factor in their spread, for example a round goby's personality traits can influence their dispersal tendency, which may also produce variation in the behavioral composition of populations at different points along their invasion fronts. To further analyze the drivers of behavioral variation within invasive round goby populations, we focused on two populations along the Baltic Sea invasion front with closely comparable physical and community characteristics. Specifically, this study measured personality within a novel environment and predator response context (i.e., boldness), and directly analyzed links between individuals' personality traits and their physiological characteristics and stress responses (i.e., blood cortisol and lactate, brain neurotransmitters). In contrast to previous findings, the more recently established population had similar activity levels but were less bold in response to a predator cue than the older population, which suggests that behavioral compositions within our study populations may be more driven by local environmental conditions rather than being a result of personality-biased dispersal. Furthermore, we found that both populations showed similar physiological stress responses, and there also appeared to be no detectable relationship between physiological parameters and behavioral responses to predator cues. Instead, body size and body condition were important factors influencing individual behavioral responses. Overall, our results reinforce the importance of boldness traits as a form of phenotypic variation in round goby populations in the Baltic Sea. We also highlight the importance of these traits for future studies specifically testing for effects of invasion processes on phenotypic variation in the species. Nonetheless, our results also highlight that the physiological mechanisms underpinning behavioural variation in these populations remain unclear., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Invasive species exert negative impacts on biodiversity and ecosystems on a global scale, which may be enhanced in the future by climate change. Knowledge of how invasive species respond physiologically and behaviorally to novel and changing environments can improve our understanding of which traits enable the ecological success of these species, and potentially facilitate mitigation efforts. We examined the effects of acclimation to temperatures ranging from 5 to 28°C on aerobic metabolic rates, upper temperature tolerance (critical thermal maximum, CT max ), as well as temperature preference ( T pref ) and avoidance ( T avoid ) of the round goby ( Neogobius melanostomus ), one of the most impactful invasive species in the world. We show that round goby maintained a high aerobic scope from 15 to 28°C; that is, the capacity to increase its aerobic metabolic rate above that of its maintenance metabolism remained high across a broad thermal range. Although CT max increased relatively little with acclimation temperature compared with other species, T pref and T avoid were not affected by acclimation temperature at all, meaning that round goby maintained a large thermal safety margin (CT max - T avoid ) across acclimation temperatures, indicating a high level of thermal resilience in this species. The unperturbed physiological performance and high thermal resilience were probably facilitated by high levels of phenotypic buffering, which can make species readily adaptable and ecologically competitive in novel and changing environments. We suggest that these physiological and behavioral traits could be common for invasive species, which would only increase their success under continued climate change., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2021. Published by The Company of Biologists Ltd.)

With the aim of understanding the molecular underpinnings of the enormous variation in the temperature sensitivity of hemocyanin-O2 affinity encountered in crustaceans, we measured O2 binding to Carcinus maenas hemocyanin at two temperatures, varying pH values and in the absence and presence of lactate ions in order to assess the contributions of oxygenation-linked binding of protons (the Bohr effect) and lactate ions to the overall enthalpies of oxygenation (DeltaH'). The hemocyanin binds maximally 0.35 lactate ions per functional subunit. Lactate (which accumulates under hypoxic conditions) increases O2 affinity by preferentially raising the association equilibrium constant of the hemocyanin in the low-affinity Tense state (KT), without significantly affecting that of the high-affinity Relaxed state (KR). In the absence of lactate, the variation in the temperature sensitivity observed with decreasing pH tallies neatly with changes in the nature and magnitude of the Bohr effect. Accordingly, the normal, absent and reverse Bohr effects observed under alkaline, neutral and acid conditions, respectively, reflect endothermic proton dissociation, absence of proton binding and exothermic proton association, respectively, upon oxygen binding. Oxygenation-linked lactate binding is exothermic, highly pH dependent and peaks near pH 7.6, where it contributes approximately -30 kJ mol(-1) to the overall heat of oxygenation. This predictably increases the temperature sensitivity of O2 affinity, potentially hampering O2 loading in warm, hypoxic habitats. The data demonstrate governing roles for lactate and proton ions in determining the temperature sensitivity of hemocyanin-O2 affinity in crustaceans.