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ABSTRACT ObjectiveWe experimentally tested whether adult Black Sea Bass Centropristis striata belonging to the northern stock could theoretically overwinter in Long Island Sound (LIS) and whether doing so would affect their survival, growth, and gonadal investment and the lipid and lean content of their gonad, liver, and white muscle tissues. MethodsFish were caught via hook and line in LIS before and after their offshore winter migration (October 2022 and May 2023, respectively). Fifty individuals from October were reared for 200 d under flow-through conditions and fed diets of crushed mussels or herring. At the end of the experiment, laboratory and wild fish were assessed for their growth, gonadosomatic index, hepatosomatic index, and tissue-specific lipid and lean contents. ResultsLaboratory fish experienced unfavorable winter temperatures (∼5–12°C) for more than 5 months, exhibiting negligible growth and high mortalities. Mortalities began accruing after temperatures had reached their seasonal minimum of about 5°C in early February (day 120). Mortalities were lower for fish on the mussel diet (40%) than for those on the herring diet (68%), but survivors from the latter group had higher tissue lipid contents. Wild Black Sea Bass returning to LIS in spring had higher tissue lipid contents and greater gonadosomatic indices than surviving laboratory fish on either diet. ConclusionsAt present, overwintering in LIS appears possible but likely disadvantageous for Black Sea Bass because offshore winter migration results in greater energy reserves and subsequent reproductive investment. In the future, however, warming coastal waters will continue to shorten the duration of unsuitable winter temperatures, which could become conducive to year-round inshore residency or partial migration patterns in the northern stock of Black Sea Bass. 

Abstract Experiments examining fish sensitivities to future oceanic CO2 levels have greatly expanded over past decades and identified many potentially affected traits. Curiously, data on reproductive trait responses to high CO2 are still scarce, despite their strong link to Darwinian fitness and thus to population vulnerability to ocean acidification. We conducted two rearing experiments on the first broadcast-spawning marine fish model (Atlantic silverside, Menidia menidia) to examine how long-term and novel whole life-cycle exposures to predicted future CO2 levels (∼2,000 µatm) affect laboratory spawning, temperature-specific reproductive investment, fecundity, and size distributions of maturing oocytes. At low temperatures (17°C), female body size and therefore potential fecundity (FPot, oocytes/female) slightly increased with CO2, while relative fecundity (FRel, oocytes/g female) remained unaffected. At high temperatures (24°C), high CO2 substantially reduced both FPot (−19%) and FRel (−28%) relative to control treatments. Irrespective of CO2, females at 24°C grew larger and heavier than those at 17°C, and although larger females produced larger oocytes at some developmental stages, they also had lower gonadosomatic indices and lower FRel. Our findings contrast with most previous studies and thus highlight the need to investigate reproductive impacts of increasing CO2 on multiple fish species with contrasting life history strategies.