Experimental setup:
50 adult specimens were collected by boat off Stonington Borough, CT (41° 20’37.8” N 71° 54’51.4” W) between September 15th and October 10th, 2022. Individuals were collected via hook and line angling and were transported in aerated coolers to the Rankin seawater laboratory where adults were acclimated and equally split between two 3785-l tanks. Each tank was supplied with flowing, sand-filtered seawater from eastern LIS which naturally ranges in temperature from 25 to 4°C and a salinity between 28 to 33 ‰. Prior to the start of the experiment adults were fed previously frozen loligo squid (Seafreeze LLC, North Kingstown RI) 3× a week ad libitum.
Experimental design:
The adult experiment assessed the inshore overwintering potential of adult BSB under two distinct diets and a current inshore temperature regime for 200 days (October 10th, 2022, to April 28th, 2023). Following each specimen collection period, a subset of individuals was immediately euthanized with an overdose of MS-222 to act as a wild ‘pre-migratory’ baseline (‘fall’, n = 17) and dissected (“see methods in “Adult black sea bass winter survival and lipid dynamics: Wild fish”).
At the start of the experiment (October 10th, 2022) 50 specimens were briefly anesthetized, measured in length (TL = 32.8 ± 6.6 cm) and weight (wW = 514.7 ± 250), tagged with monofilament Floy-tags, and randomly allocated to one of two 3785-l tanks which was allocated a diet treatment; ‘mussels’ (Mytilus edulis; American Mussel Harvesters, North Kingston RI) and ‘herring’ (Clupea harrengus; Seafreeze ltd., North Kingston RI).
Fish were then fed 2% of the initial stocked biomass 3× a week throughout the experiment. Experimental tanks were flow-through (9060 l h-1), with conditions ambient to local LIS conditions and had a set of lights whose photoperiod was gradually changed weekly (11.5 h light: 12.5 h dark to 9 h light: 15 h dark and back up). Temperature was monitored in one tank by a Eureka Manta probe which recorded tank temperature every 30 minutes, while pH was monitored twice weekly via a handheld pH probe (Hach Handheld HQ40D), ammonia and salinity were measured once a week, and each tank was siphoned twice weekly to remove detritus. Over the course of the experiment there was no ammonia (0 ppm), while the mean pH and salinity were 8.04 ± 0.12 pH units and 31.8 ± 1.07 ‰, respectively.
Over the course of the experiment, fish were examined twice daily for mortalities or loss of equilibria. In the case of lost equilibria, specimens were immediately removed, euthanized with an overdose of MS-222, and dissected as previously described. Over the course of the experiment three individuals from the Herring diet treatment jumped overnight and weren’t included in subsequent analyses.
Since C. striata tend to have a high site-fidelity, beginning of April 2023, sampling occurred weekly on the same reef that the experimental and fall baseline specimens were collected on in order to collect ‘post-migratory’ baseline specimens (‘spring’, n = 21), upon their first entry into LIS (April 27th, 2023; see methods in “Adult black sea bass winter survival and lipid dynamics: Wild fish”). Specimens were immediately euthanized, measured, and dissected as previously described and the experiment ended the following day (April 28th, 2023). Upon ending the experiment all surviving specimens were measured for length (TL; 33.7 ± 4.4 cm), body depth (BD; 8 ± 0.9 cm), and wet weight (wW; 532.6 ± 227 g). During dissections, the stomach was removed to calculate a stomachless whole weight to standardize for consumed prey items, and the liver and gonad was then removed, individually weighed (0.01 g) and frozen at -20°C for future lipid extractions. A subsample of dorsally located white muscle tissue was also removed and frozen.
Response traits:
For experimental adults, we only calculated cumulative growth in length (GR), and specific growth rates (SGR). For all adults, we calculated gonadosomatic (GSI; %) and hepatosomatic (HSI; %) indices using stomachless fish mass (wW – stomach mass), to standardize for stomach contents, as {e.g., 100 × [(gonad or liver mass, g) / (stomachless fish mass)].
We quantified gonad, liver, and white muscle, storage lipid, lean-mass, and ash weights of each surviving experimental individual and baseline specimen. Samples were frozen at -50°C for 1 week and remeasured for whole body dry weight (dWb, 0.001 g). Following published protocols (Schultz and Conover 1997, Guo et al. 2021, 2022, Zavell et al. 2023), dried specimens were loaded into preweighed Alundum medium-porosity extraction thimbles and transferred to a custom-designed Soxhlet apparatus, where they were bathed in petroleum ether for 3.5 h to extract all metabolically available lipids. Samples were then dried overnight (60°C) and re-measured, with the change in pre- and post-extraction weights (ΔdW), representing the storage-lipid fraction (dWLipid). Samples were then muffle furnaced for 4 h at 550°C and reweighed with ΔdW, representing the lean-mass fraction (dWLean) and the remaining mass represents the inorganic fraction (dWAsh).
Organism Identifier (LSID, Life Sciences Identifier)
Centropristis striata, urn:lsid:marinespecies.org:taxname:159348
