Hemolymph osmolality and cation concentrations in Litopenaeus vannamei during exposure to artificial sea salt or a mixed-ion solution: Relationship to potassium flux

Interest in culturing the Pacific white shrimp Litopenaeus vannamei in low-salinity and brackish-well waters has led to questions about the ability of this species to osmo- and ionoregulate in environments containing low concentrations of ions and in environments with ionic ratios that differ from those found in sea water. After seven days, hemolymph osmolality and potassium, sodium and calcium values were all significantly affected by salinity (as artificial sea salt) with values decreasing with decreasing salinity. These decreases were small, however, relative to decreases in salinity, indicating iono- and osmoregulation with adjustment for gradients. The hemolymph osmolality and sodium and calcium concentrations in shrimp exposed to either 2 g/L artificial sea salt or 2 g/L mixed-ion solution (a mixture of sodium, potassium, calcium, and magnesium chlorides that approximate the concentrations and ratios of these cations found in 2 g/L dilute seawater) did not differ significantly. However, hemolymph potassium levels were significantly lower in shrimp held in the mixed-ion environment. Potassium influx rates were similar in shrimp held in either artificial sea salt or mixed ions. The results of this study indicate that salinity affects hemolymph-cation concentrations and osmolality. Further, differential potassium-influx rates do not appear to be the basis for low hemolymph potassium levels observed in shrimp held in mixed-ion environments

The Use of Tricaine Methanesulfonate, Clove Oil, Metomidate, and 2-Phenoxyethanol for Anesthesia Induction in Alewives

The efficacy of four anesthetic agents—tricaine methanesulfonate (MS-222), clove oil, metomidate, and 2-phenoxyethanol (2-PE)—was studied in adult, juvenile (133.3 ± 1.5 mm, 27.5 ± 8.9 g; mean ± SE), and larval Alewives Alosa pseudoharengus. In an initial trial, wild-caught adults were anesthetized to a state where they failed to respond to strong tactile stimuli when dosed with 87.5–112.5 mg/L MS-222, 25–40 mg/L clove oil, 0.5–5.0 mg/L metomidate, and 125–550 mg/L 2-PE. Optimal doses for anesthesia, defined as those providing the combined shortest induction and recovery times, were similar for larvae and juveniles: 75–100 mg/L MS-222, 40 mg/L clove oil, 5–7 mg/L metomidate, and 500 mg/L 2-PE. All juvenile fish survived 48 h postexposure to each optimal dose. In a longer (24 h) sedation experiment, juvenile Alewives were netted and exposed to low clove oil (2.5 and 5.0 mg/L) and metomidate (0.25 and 0.50 mg/L) doses, after which plasma cortisol was measured. Fish exposed to the clove oil treatments exhibited a cortisol stress response that was prolonged in the higher-dose treatment. No cortisol stress response was observed in the metomidate treatments. Overall, optimal acute anesthesia doses for Alewives were similar to those reported for other species, and metomidate may be useful for longer-term sedation