Seasonal changes in phosphorus content of fish tissue as they relate to diets of renal patients.

OBJECTIVE: To investigate seasonal variations in tissue phosphorus (P) levels, P to protein ratio, and P to omega-3 fatty acid (ω3-FA) ratio in 2 species of fish that are commonly consumed in Lebanon. We aim to determine suitability for dietary management of renal patients. DESIGN AND SETTING: Siganus rivulatus (rabbitfish) and Diplodus sargus (white seabream) were caught in traps off the coast of Beirut and transported on ice to the laboratory during various seasons. Fillets of fish were removed, dried to constant weight at 95°C, finely ground, and stored at -20°C. Protein, P, P to protein ratio, and P to ω3-FA ratio were determined. RESULTS: Compared with white seabream (carnivore), rabbitfish (algaevore) had a significantly lower mean P content (±SE) (895 ± 32 mg/100 g vs. 1,132 ± 23 mg/100 g; P < .0001), a significantly lower P to protein ratio (±SE) (10.35 ± 0.39 vs. 13.15 ± 0.34 mg P/g of protein; P < .001), and a significantly lower P to ω3-FA ratio (±SE) (2.81 ± 0.29 vs. 5.93 ± 1.05 g of ω3-FA/g of P; P < .005). P content in flesh of both species varied significantly with season (P < .0001). Rabbitfish P content was least in August and greatest in June (P < .05), whereas white seabream P content was greatest in April and least in June (P < .05). Rabbitfish muscle P to protein ratio and P to ω3-FA ratio was least in August, with a significantly greater P to ω3-FA ratio during the rest of the year. White seabream exhibited wider seasonal variation in P to protein ratio and P to ω3-FA ratio as compared with rabbitfish. CONCLUSION: Because of differences and seasonal variations in P levels that exist among fish species, renal dietitians may need to identify the seasonal proximate composition of individual fish species in various habitats and formulate dietary regimens accordingly. Such advice notwithstanding, oily marine fish remain a healthy food choice for dialysis patients if the fillet is consumed without bones.

Branchial carbonic anhydrase activity and ninhydrin positive substances in the Pacific white shrimp, Litopenaeus vannamei, acclimated to low and high salinities.

The Pacific white shrimp, Litopenaeus vannamei, acclimated to 30 ppt salinity, was transferred to either low (15 and 5 ppt), or high (45 ppt) salinity for 7 days. Hemolymph osmolality, branchial carbonic anhydrase activity, and total ninhydrin-positive substances (TNPS) in abdominal muscle were then measured for each condition. Hemolymph osmotic concentration was regulated slightly below ambient water osmolality in shrimp acclimated to 30 ppt. At 15 and 5 ppt, shrimp were strong hyper-osmotic regulators, maintaining hemolymph osmolality between 200 and 400 mOsm above ambient. Shrimp acclimated to 30 ppt and transferred to 45 ppt salinity were strong hypo-osmotic and hypo-ionic regulators, maintaining hemolymph osmolality over 400 mOsm below ambient. Branchial carbonic anhydrase (CA) activity was low (approximately 100 micromol CO(2) mg protein(-1) min(-1)) and uniform across all 8 gills in shrimp acclimated to 30 ppt, but CA activity increased in all gills after exposure to both low and high salinities. Anterior gills had the largest increases in CA activity, and levels of increase were approximately the same for low and high salinity exposure. Branchial CA induction appears to be functionally important in both hyper- and hypo-osmotic regulations of hemolymph osmotic concentrations. Abdominal muscle TNPS made up between 19 and 38% of the total intracellular osmotic concentration in shrimp acclimated to 5, 15, and 30 ppt. TNPS levels did not change across this salinity range, over which hemolymph osmotic concentrations were tightly regulated. At 45 ppt, hemolymph osmolality increased, and muscle TNPS also increased, presumably to counteract intracellular water loss and restore cell volume. L. vannamei appears to employ mechanisms of both extracellular osmoregulation and intracellular volume regulation as the basis of its euryhalinity.