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Over the last decade, ocean temperature on the U.S. Northeast Continental Shelf (U.S. NES) has warmed faster than the global average and is associated with observed distribution changes of the northern stock of black sea bass ( Centropristis striata ). Mechanistic models based on physiological responses to environmental conditions can improve future habitat suitability projections. We measured maximum, standard metabolic rate, and hypoxia tolerance (S crit ) of the northern adult black sea bass stock to assess performance across the known temperature range of the species. Two methods, chase and swim-flume, were employed to obtain maximum metabolic rate to examine whether the methods varied, and if so, the impact on absolute aerobic scope. A subset of individuals was held at 30°C for one month (30 chronic °C) prior to experiments to test acclimation potential. Absolute aerobic scope (maximum–standard metabolic rate) reached a maximum of 367.21 mgO 2 kg -1 hr -1 at 24.4°C while S crit continued to increase in proportion to standard metabolic rate up to 30°C. The 30 chronic °C group exhibited a significantly lower maximum metabolic rate and absolute aerobic scope in relation to the short-term acclimated group, but standard metabolic rate or S crit were not affected. This suggests a decline in performance of oxygen demand processes (e.g. muscle contraction) beyond 24°C despite maintenance of oxygen supply. The Metabolic Index, calculated from S crit as an estimate of potential aerobic scope, closely matched the measured factorial aerobic scope (maximum / standard metabolic rate) and declined with increasing temperature to a minimum below 3. This may represent a critical threshold value for the species. With temperatures on the U.S. NES projected to increase above 24°C in the next 80-years in the southern portion of the northern stock’s range, it is likely black sea bass range will continue to shift poleward as the ocean continues to warm.

The highly migratory nature of bluefish Pomatomus saltatrix makes comprehensive study of their populations and their potential responses to factors such as competition, habitat degradation, and climate change difficult. Body composition is an important ecological reference point for fish; however, estimating body composition in fish has been limited by analytical and logistical costs. We applied bioelectrical impedance analysis (BIA) to estimate one body composition component (percent dry weight) as a proxy of condition in bluefish. We used a tetra polar Quantum II BIA analyzer and measured electrical properties in the muscles of bluefish at two locations per fish (dorsal and ventral). In total, 96 bluefish ranging from 193 to 875 mm total length were used in model development and testing. On 59 of these fish BIA measures were taken at both 15 • C and 27 • C. Temperature had a significant negative effect on resistance and reactance. A subsample of these fish was then analyzed for dry weight as a percentage of their whole body weight (PDW), which is a good indicator of condition because it is highly correlated with fat content in fish. The BIA models predicting PDW inclusive of all lengths of bluefish were highly predictive for 15 • C (stepwise regression) and 27 • C. Regression (R 2 pred ) values that estimate future predictive power suggest that both models were robust. Strong relationships between PDW and other body composition components, coupled with the BIA models presented here, provide the tools needed to quantitatively assess bluefish body composition across spatial and temporal scales for which assessment was previously impossible.The growth of fish is believed to be an integrated measure of well-being that is linked to reproductive success, survival, habitat quality, and competition (Brandt et al. 1992;Roy et al. 2004;Amara et al. 2009;Vehanen et al. 2009). In aquaculture and other applications, such as those employing fish bioenergetics models, growth is often determined by measuring differences in the total weight of fish over time. However, fish are 60-90% water, and they often compensate for loss of fat by replacing it with water, making the use of total weight to measure growth and condition problematic (Shearer 1994;Breck 2008;Hartman and Margraf 2008). To fully evaluate growth in weight of fish requires knowledge of the percent dry mass of the fish. Dry mass can be measured on an individual by oven drying or by freeze drying but, in addition to being lethal, this process can be cumbersome for large individuals or impossible for rare taxa.Bioelectrical impedance analysis (BIA) has been used to determine water mass in human subjects since the 1970s and is now widely used in health clubs to assess human body condition. 307 308 HARTMAN ET AL.

Abstract. The limited available evidence about effects on marine fishes of high CO2 and associated acidification of oceans suggests that effects will differ across species, be subtle, and may interact with other stressors. This report is on the responses of an array of early life history features of summer flounder (Paralichthys dentatus), an ecologically and economically important flatfish of the inshore and nearshore waters of the Mid-Atlantic Bight (USA), to experimental manipulation of CO2 levels. Relative survival of summer flounder embryos in local ambient conditions (775 μatm pCO2, 7.8 pH) was reduced to 48% when maintained at intermediate experimental conditions (1808 μatm pCO2, 7.5 pH), and to 16% when maintained at the most elevated CO2 treatment (4714 ppm pCO2, 7.1 pH). This pattern of reduced survival of embryos at high-CO2 levels at constant temperature was consistent among offspring of three females used as experimental subjects. No reduction in survival with CO2 was observed for larvae during the first four weeks of larval life (experiment ended at 28 d post-hatching (dph) when larvae were initiating metamorphosis). Estimates of sizes, shapes, and developmental status of larvae based on images of live larvae showed larvae were initially longer and faster growing when reared at intermediate- and high-CO2 levels. This pattern of longer larvae – but with less energy reserves at hatching – was expressed through the first half of the larval period (14 dph). Larvae from the highest-CO2 conditions initiated metamorphosis at earlier ages and smaller sizes than those from intermediate- and ambient-CO2 conditions. Tissue damage was evident in larvae as early as 7 dph from both elevated-CO2 levels. Damage included dilation of liver sinusoids and veins, focal hyperplasia on the epithelium, and separation of the trunk muscle bundles. Cranio-facial features changed with CO2 levels in an age-dependent manner. Skeletal elements of larvae from ambient-CO2 environments were comparable or smaller than those from elevated-CO2 environments when younger (7 and 14 dph) but were larger at developmental stage at older ages (21 to 28 dph), a result consistent with the accelerated size-development trajectory of larvae at higher-CO2 environments based on analysis of external features. The degree of alterations in the survival, growth, and development of early life stages of summer flounder due to elevated-CO2 levels suggests that this species will be increasingly challenged by future ocean acidification. Further experimental studies on marine fishes and comparative analyses among those studies are warranted in order to identify the species, life stages, ecologies, and responses likely to be most sensitive to increased levels of CO2 and acidity in future ocean waters. A strategy is proposed for achieving these goals.

ABSTRACT:The relationship between the growth of early juvenile winter flounder (Psuedopleuronectes americanus, Walbaum; 17 to 27 mm standard length [SL]) and the spatial dynamics of estuarine gradients immediately following larval settlement was examined using field enclosure techniques in a temperate nursery. Enclosures (n = 60; 3 fish per enclosure) were deployed throughout the Navesink River/Sandy Hook Bay estuarine system, New Jersey, in a nested spatial design that allowed measurement of growth variation in time at 3 spatial scales (between regions: × -distance [D]

The effects of constant and diurnally fluctuating levels of dissolved oxygen on the growth of young-of-theyear winter flounder, Pseudopleuronectes americanus, were examined under controlled laboratory conditions. Fish were exposed for either 10 or 11 weeks to constant levels of 6.7 (high) and 2.2 (low) mg l-l, and a diurnal fluctuation, ranging from 2.5 to 6.4 mg O2 1-l. Growth rates, calculated for both standard length and weight, for fish exposed to low and diurnally fluctuating levels were significantly reduced (p < 0.001) as compared to those for fish exposed to the high level. Growth rates of fish exposed to the high level were over twice those of fish held under low oxygen conditions. Under fluctuating conditions, fish grew at intermediate rates. Following these exposures, all fish were subsequently held at 7.2 mg O? 1-l for five weeks. Growth rates increased over two and a half times for fish previously exposed to the low oxygen level and were significantly (p < 0.001) higher than for the other two groups.