Physiological Changes in the Red Drum after Long-Term Freshwater Acclimation |
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| Authors: | Mariel Gullian-Klanian |
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| Institution: | Universidad Marista de Mérida, Periférico Norte Tablaje Catastral 13941 Carretera Mérida-Progreso , Post Office Box 97300, Mérida , Yucatán , Mexico |
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| Abstract: | Abstract The effect of long-term freshwater acclimation on the blood and plasma ion composition of Red Drum Sciaenops ocellatus was investigated with the goal of elucidating the necessity of ion remediation. Four replicates (n = 50) of freshwater-acclimated (FW) fish (1.6 ± 0.2 g) were raised in 25-m3 tanks supported by 140,000 L of recirculating water. Four replicates (n = 50) of seawater (SW) fish groups were placed in 40-m3 offshore cages at 32–35 psu. Blood was collected from 100 fish (FW = 578 ± 50 g; SW = 686 ± 45 g) of each group (FW, SW) after 8 months of rearing. During the grow-out phase, the survival of FW and SW fish was 57.5% and 92.2%, respectively. The water ion composition (mainly the Ca2+/K+ 43%] and Ca2+/Mg2+ ratios 1%]) explained 56.6% of the plasmatic ion variability in the fish groups. Freshwater exposure produced significant reductions in osmolality and in several plasma indicators (Na+, Cl?, and Mg2+); the K+ levels from FW fish were the most compromised parameter. The water Ca2+/Na+ ratio had a greater influence (44%) on the plasma chemistry parameters, mainly glucose and creatinine. Freshwater-acclimated fish had a higher percentage of hematocrit, hemoglobin, and red blood cells than SW fish, but the water quality explained only 12.5% of the blood parameter variability between the FW and SW groups. The results support the conclusion that Red Drum tolerates salinity variations and can adopt a relatively stable condition for short periods; however, the data suggest that Red Drum have only a limited ability to withstand a hyposmotic environment for long periods due to their limited ability in maintaining K+ concentrations without external supplementation. Freshwater environments with high Ca2+/Na+, Ca2+/K+, and Ca2+/Mg2+ ratios appear to be a chronic stress factor that should be considered in future experiments. Received June 11, 2012; accepted March 17, 2013 |
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