Review: Phosphorus in Fish Nutrition

diet. Schäfer et al. (1995b) fed common carp for 63 days with a soybean meal-fish meal based diet (ca. 0.24%
available P/DM) with or without supplemental Ca(H 2PO 4) 2. The fish growth and the contents of ash and P in
dorsal scales and whole body increased in proportion to the amount of P added to the basal diet (ca. 0.42 or 0.60%
available P/DM). The backbone (defatted) and opercula seems to be less sensitive than scales to dietary available P
concentrations. Kim et al. (1998) estimated dietary available P requirement for mirror carp to be about 0.7% for
the maximum growth and minimum loss of P (per kg wt gain). The feed conversion of the diets was about 1.0
(max). Fish (body wt, initial 18 g; final max 44 g) were fed diets containing fish meal, soybean meal, wheat flour,
etc. with varied levels of P supplied as Ca(H 2PO 4) 2. The authors calculated the available P content of the
P-supplemented diets assuming that the P in Ca(H 2PO 4) 2 was 90% available. The final body P content of the fish
was similar among treatments, but wt gain of the fish clearly responded to the dietary P concentrations. The initial
fish had even lower concent ration of P in the body than fish fed the diet of the lowest P content (0.24% available P)
for 8 weeks. This suggests that the dietary requirement might be overestimated since P-deficient fish require P not
only for growth but also for replenishing the body P pool. The retetion plateau of P has been shown to be
influenced by the P status of the body or previous diet history (Edwards & Gillis 1959, Sugiura et al. 2000).
P requirement in Salmonids
Ketola (1975) studied the dietary requirement of P for Atlantic salmon based on weight gain, feed conversion and
bone ash content. Incremental amounts of P were added to the basal diet containing soybean meal (70%) and
CaCO 3 (3%). Fish grew from 6.5 g to only 9.8 g (max.) during a 5 wk feeding period with feed conversion ranging
1.69-2.75. Although the basal diet contained 0.7% total P, the content of available P might be substantially low
(not measured). The Ca added to the basal diet could precipitate phytate-P and some Pi. Ogino & Takeda (1978)
estimated dietary P requirement for rainbow trout in a 6 wk feeding trial using egg albumin-based diets of four P
levels and two Ca levels. Fish consuming P-adequate diets increased their initial weight about 3 times (initial wt.
1.2 g, final max wt. 3.6 g) with the feed efficiency of 1.1 (max). The dietary requirement of availabl e P for the
normal growth was between 0.32 and 0.64% in the low-Ca diet, and more than 1.1% (no plateau) in the high-Ca diet
(the authors concluded di fferently). Levels of Ca and P in the whole body of fish fed the low-Ca diet increas ed
proportionately to the dietary P levels (no plateau); however, the ash level reached the plateau at 0.64% P in the diet.
Among fish fed high-Ca diets, there seemed to be no plateau at all for ash, Ca and P contents in the body. The P
availability (absorption) in the low-Ca and high-Ca diets was not measured. Watanabe et al. (1980) determined
the dietary P requirement for chum salmon (initial wt. 1.5 g, final max. wt. 4.9 g) in a 7 wk-feeding trial. Fish were
fed four times daily to apparent satiation. Feed effi ciency ranged from 33% (lowest P) to 101% (adequate P).
The diets contained ~0.37% Ca supplied primarily as Ca lactate. The absorption (availability) of dietary P was not
measured. The estimated dietary P requirement for growth and bone development was 0.5-0.6% as total P. Fish
receiving the diet of the lowest P content had markedly lower fat content in the body and viscera, which is an
opposite observation from others. Ketola (1985) devised a new, low-cost diet that contained only a modest amount
of P supplied mainly from defluorinated rock phosphate. He claimed that the diet supported "significantly slower,
but adequate growth" and reduced P pollution by more than 50%. The P pollution that the author meant was the
soluble P that was not retained by the fish. This soluble fraction of P excreted by fish generally represents dietary
available P that was absorbed by the fish and excreted subsequently via urine due to an excess intake. Apparently,
the total P in diets was more than the dietary requirement since the basal diet contained soybean meal and casein (or
corn gluten meal) as the major ingredients, and this diet was further supplied with either dicalcium phosphate or
defluorinated rock phosphate in the amount about the dietary requirement for the fish. Depending on the
availability of P in these P sources, the fish simply excrete an excess portion as soluble P. This excess portion must
be reduced by reducing the amount of available (excess) P in the diet to the minimum requirement level for the fish.
Unfortunately, the author reported neither the amount of P retained by the fish (body P content) nor the amount
excreted into feces (P availability), nor even the total amount of P in the diets. Vielma & Lall (1998a) fed Atlantic
salmon (initial wt 15 g) to satiation for 16 wk. The basal diet containing 4 mg P/g (0.15 mg available P per KJ DE)
was supplemented with eight graded levels of Ca(H 2PO 4) 2·H 2O. The fish required 0.28 mg available P per KJ DE.
Increasing dietary P increased P and Ca levels in plasma and bone, whereas liver cholecalci ferol level decreased.
In P-defi cient fish, the urine P concentration was 0.10 mmol/L before feeding and 0.25 mmol/L after feeding,
whereas in P-replete fish these concentrations were 1.09 and 5.11 mmol/L, respectively. The apparent absorption
of P was lower in P-replete fish than in P-deficient fish. Vielma et al. (2002) reported significantly lower tolerance
of whitefish against high water temperature in dietary P restriction. But, there was no detectable difference in
low-oxygen tolerance in dietary P deficiency.
© 2000, 2005. Shozo H. Sugiura. All rights reserved.
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