Review: Phosphorus in Fish Nutrition

substance, we commonly find that, during the latter months of pregnancy, the urine hardly contains more than traces
of it, even when the diet has been sufficiently abundant (p. 128)." He also wrote, "The amount of the excreted
phosphoric acid is . . . diminishing during prolonged abstinence, without, however, like the chloride of sodium,
finally altogether disappearing (Schmidt observed that after prolonged abstinence, a cat excreted daily only
one-third of the normal quantity of phosphoric acid. Mosler has made similar observations on man (p. 319)."
Bischoff (1867) found that when dogs were fed lean beef P was excreted about 12-thirteenths in the urine, mostly
combined with the alkalis, while the reminder left the body in the feces combined principally with Ca, Fe and Mg.
On a diet of bread, a much larger amount of P appeared in the feces. Anderson's book published in 1878 is full of
radical hypotheses (mostly incorrect, but entertaining) with few references. The basic theory that he called
"capillary nutrition" was based on the observation that inorganic and nitrogenous materials were continuously
excreted in urine, and on the assumption that various diseases were deficiency of available forms of mineral
compounds in food. He wrote, "The diseases of nutrition, where the chemical composition of tissue undergoes
alteration, are--- starvation, arising from general innutrition; fatty degeneration, dependent on organic innutrition
(defici ency of albuminates in flesh); and the diseases which on the theory here advocated depend upon inorganic
innutrition. These last are scurvy, rickets, scrofula, consumption, cancer, and leprosy (p. 94)." Anderson
incorrectly concluded that urinary excretion of phosphate was due to matamorphosis of tissues (tissue renewal) and
phosphorus used for brain and nerve, and thus the phosphorus excreted in urine was obligatory loss. From this, and
his ballpark calculation of phosphorus balance, he suggested phosphorus deficiency was very likely (and thus causes
"scurvy") (p. 110-111). He also wrote, "Many articles of food materially increase the quantity of phosphoric acid
voided in the urine. An invalid, fed on milk alone, passes 5.5 grammes of phosphoric acid in his urine; beer, also,
must have the effect of increasing the secretion of this acid, as phosphoric acid exists in appreciable quantities in
beer. Phosphoric acid arising from such sources as this can take no part in nutrition; in order to arrive at anything
like an accurate estimate of the quantity of phosphoric acid taking part in nutrition, these sources of error should be
avoided (p. 63)." Apparently, he was aware that any excess of dietary P is excreted in urine and is useless in
nutrition. Leder (1881) fed dogs with 500 or 1000g of meat of either raw or cooked, and found that the peak
excretion of P and sulfur in urine occurred during the second hour, while the nitrogen peak did not occur until 4th
hour. All had dropped to normal in 12 hours. In humans, North (1883) found that about equal quantities of P in
foods were excret ed by the kidney and by the bowel. Gevaerts (1901) found that P excretion in the urine of white
rats consuming a P-free diet was very much less in the amount than P present in the urine during starvation; and that
on a ration of sucrose and edestin, or on sucrose and ovalbumin, there was much less P in the urine than on a ration
of sucros e alone. Plimmer et al. (1909-1910) found that Pi in urine constitutes 90-100% of the whole. They
wrote, "The quantity (of Pi) excreted (in urine) depends entirely on the intake of P 2O 5 . . . (conversely) the daily
output (of the organic P 2O 5) in our subject was extremely irregular; . . . The organic P 2O 5 in the urine is therefore
uninfluenced by diet and must originate in the body, i.e. it must be endogenous." (-- words in parentheses were
added). Maurel (1901, 1904) estimated daily P requirement in normal diets by experimenting on himself and
based solely on the urinary P excretion. Heubner (1909) produced rickets by feeding two young dogs a
P-deficient diet (egg-white based diet) for 7 weeks. Three other dogs received a high-P ration containing casein
and P-supplement, etc. The P content of the urine differed greatly, and corresponded to the amount of P in the diet.
The P content in the feces of these dogs, however, was similar throughout the period and was unrelated to the food.
Wolf & Oesterberg (1911) noted that feeding starving dogs with a small amount of protein reduced urinary P
excretion to a very low level, while feeding starch and fat had little or no effect on P excretion. Denis (1912-13)
collected urine from dogfish (elasmobranch) quantitatively for 24 h. The fish were tied by means of inch wide
bandages to a board about 2 feet in length, which was placed in a large tank of running seawater and fastened in
such a position that the cloaca was raised above the surface of the water. The urine was collected through the
cannula tied to the urinary papilla. Alternatively, some fish were placed in a narrow trough without fastening the
fish to a board. The author noted that pithing (destroying) the spinal cord up to about the level of the dorsal fin was
helpful. The urine was analyzed for many components, and the average P concentration of 10 dogfish (fasting) was
4520 ppm as P 2O 5 (= 1973 ppm as P). The urine was acidic, and when neutralized earthy phosphates precipitated.
Denis (1913-14) analyzed urine of goosefish (teleost) collected from the bladders of 6 fish after death. The urine
contained 440 ppm as P 2O 5 (= 192 ppm as P). Smith (1930, 1932) demonstrated that essentially all of the
absorbed P, Mg, Ca, and sulfate which leave the body are excreted by the kidney alone. In humans (Grosser 1920)
and dogs (Salvesen 1923), it has been shown that even when calcium is injected subcutaneously, it is excreted
mainly by the bowel; whereas under similar conditions P is passed in the urine, and no increase being noted in the
feces. Grafflin (1936) concluded that the glomerular kidney of sculpin as well as the aglomerular kidney of the
goosefish and toadfish excretes Pi that is derived from some unidentifi ed precursor other than Pi in the plasma.
Kaune & Hentschel (1987) reported that goldfish excrete P by regulating renal tubular reabsorption as well as renal
© 2000, 2005. Shozo H. Sugiura. All rights reserved.
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