Review: Phosphorus in Fish Nutrition

was lower and Pi/total P ratio was higher than when fish were stocked at normal density. McCartney (1971a)
determined Pi, nucleic acid-P, phosphoprotein-P, lipid-P, barium-precipitated P in the erythrocytes of three trout
species. McCartney (1971b) det ermined in brook trout the effect of dietary glucose, fructos e and galactose on
plasma P levels at various fractions, including Pi, lipid-P, phosphoprotein-P, nucleic acid-P, fructose 6-phosphate and
fructose 1,6-bisphosphate. Pi (153-171 ppm) and lipid-P (130-139 ppm) dominated the plasma total P (307-328
ppm) regardless of the dietary treatments. Fish fed fructose, however, had higher levels of phosphoprotein-P and
nucleic acid-P, and those fed glucose had higher levels of fructos e 6-phosphate and fructos e 1,6-bisphosphate than
those fed the other nonsaccharides. In higher animals, administration of glucose or fructose is known to cause
acute hypophosphatemia (Berner & Shike 1988, IOM 1997). Hammond & Hickman (1966) found that the
plasma Pi of rainbow trout increased rapidly with strenuous exercise, but took 1-8 hours to return to the original
level. Hille (1982) reviewed literatures on blood analyses of rainbow trout, and presented the normal ranges of
various blood components and factors that might affect such measurements. He wrote: Cardiac sampling is the
only suitable way since blood withdrawal from caudal vessels is subjected to contamination of tissue fluid. Plasma
containing EDTA (as an anticoagulant) is unsuitable for the analyses of P, AP, and among others. The plasma
concentration of phosphoprotein-P is about 0.25 ppm, which increases with estrogen during maturation. Serum
phosphate does not depend on food phosphate supply (sic.). Compared with mammals, trout plasma contains large
amounts of phospholipids, between 4610-8250 ppm. Hrubec & Smith (1999) reported that P values were higher
in the serum than in plasma in all species tested (rainbow trout, hybrid striped bass, channel catfish, and hybrid
tilapias). The authors suggested that the difference observed between serum and plasma most likely represents
metabolic utilization of blood constituents while the blood was clotting.
IOM (1997) used serum Pi concentration as the criteria to estimate dietary P requirement for humans. In
turkey, however, Hurwitz et al. (1978) reported that plasma Pi increased linearly with absorbed P, while P retention,
bone ash and weight gain all plateaued. Baeverfjord et al. (1998) did not find differences in plasma total P or Ca
levels between P-depleted and P-suffici ent Atlantic salmon. Skonberg et al. (1997) concluded that blood plasma P
levels were insensitive and fallacious as a response indicator of P status of fish because (1) blood P levels tend to
reflect recent dietary intake more than the actual P status of the fish, (2) different methods measure di fferent
fractions of P in the serum, plasma or whole blood (i.e., not only inorganic P but various acid-labile organic P
compounds), and (3) non-nutritional factors, such as sampling time (aft er meal), handling of the samples, collection
methods, temperature, salinity, and various stresses on fish when or before sampling, also have profound effects on
the blood P level. The authors collected plasma from rainbow trout (body wt 1.9-5.3 g) that had been starved for
1.5 days, and found little difference in the P concentration among fish fed diets of varied P levels. Vielma & Lall
(1998b) reported a large difference in plasma P concentrations between samples collected 4 h after feeding and those
collected 24 h aft er feeding. Thus, when estimating fish’s P status or adequacy of dietary P intake, the serum or
plasma P, though sensitive, may not be reliable, unless the sampling procedure, especially feed intake of each fish
and the postprandial sampling time, is well-controlled. Bureau & Cho (1999) reported the relationship between
plasma P concentration and urinary P excretion. But, as these authors suggested, plasma Pi is highly variable over
the whole day, and this may complicate the use of plasma Pi measurement to estimate urinary P output of fish (c.f.
section “ Urinary P”).
Response criterion: Urinary P
Phosphorus was first discovered from urine in 1667 by Brandt who believed that human urine contained something
that could convert silver into gold. Having been disappointed, he did not publish this discovery for years. Liebig
(1842) wrote that the urine of carnivores is acidic and contains large amounts of alkaline bases united with uric,
phosphoric, and sulfuric acids, and that these salts in blood are separated in the kidney. He believed that P in urine
was derived from the "metamorphosed tissues" (p. 76). Liebig also wrote that the urine of gramnivora (e.g.,
horses) contains only traces of P, and a large amount of carbonates. He considered the difference in urinary P
content between carnivora and hervivora as due to different rat es of tissue metamorphosis. Lehmann's book
published in 1850 and translated into English in 1851 also reported a similar hypothesis, "The constant occurrence
of phosphate of lime . . . obviously strengthen the opinion that this substance plays an important part in the
metamorphosis of the animal tissues, and especially in the formation and in the subsequent changes of animal cells
(p. 416)." Aubert (1852) found that while his normal daily excretion of phosphoric acid was 2.8g, it rose to 4.1g
after he had swallowed 31g of phosphate of soda. Sick (1857) found that the ingestion of sodium P increased
urinary P by more than the added amount, with a decrease of earth P and an increase of alkali P. Day (1860) wrote,
"The quantity of phosphate of lime in the urine is dependent on the quantity of this substance occurring in the food,
and on the demands of the organism for this salt. From the great demand on the part of the foetus for this
© 2000, 2005. Shozo H. Sugiura. All rights reserved.
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