Review: Phosphorus in Fish Nutrition

and feed effi ciency were used as respons e criteria. In the first trial, large fish (initial wt. 321 g) were fed for 14
weeks but they gained only ca.30%. Consequently, the differences among treatments were very small. In the
second trial, fish (initial wt 7.9 g) doubled their weight after 6 weeks of feeding with diets of varied P levels (5
levels ranging 0.15-0.95%P). In the 3rd trial, fish grew only from 48 g to 61-72 g after 10 weeks of feeding, and
the responces of fish to dietary P levels (5 levels ranging 0.30-0.62%P) were no clear. The authors determined the
P requirements in the 2nd and 3rd trials based on each of the foregoing respons e criteria, and took an average. The
averaged dietary P requirement for optimum growth, feed effici ency and serum P level was 0.29%, whereas that for
ash, Ca, P in scales, vertebra, and dorsal fin was 0.58% as total P (available P was not measured). They also
reported 15% of fish fed P deficient diet had scoliosis, which could be due to vitamin C defici ency (see below).
Shim & Ho (1989) tested 3 levels of Ca and 3 levels of P to estimate dietary requirements of Ca and P for guppy,
Poecilia reticulata. Dietary Ca levels did not affect the growth but P levels affected growth, feed conversion and
bone ash, Ca and P levels. The authors concluded that the P requirement was between 0.53 and 1.23%. The highest
feed effi ciency was about 36%, and the fish only doubled the weight after 12 weeks of satiation feeding. The basal
diet contained 43% of cas ein (P content in casein is notoriously high), but the analytical data showed the diet
contained only 0.05% P/diet. The authors reported bone deformity such as scoliosis, lordosis and broken-back in
the group of fish fed diets without supplemental P. The P sources most commonly used in P requirement studies
are KH 2PO 4 and NaH 2PO 4. Supplementing test diets with such P sources lower dietary pH, which stabilizes
ascorbic acid in the diets during processing and storage. Thus, low-P diets could likely become defi cient in vitamin
C, unless the vitamin is stabilized or overforti fied. According to Rose (1938), "Rickets is a disease of the entire
bone; scurvy affects the growing ends. In rickets, the bone tends to bend; in scurvy, to break". In fish, this is also
the case; the broken-back syndrome is the sign of vitamin C defici ency (e.g., Lovell 1973), while bending bones are
the sign of P defici ency (e.g., Shearer & Hardy 1987). Baeverfjord et al. (1998) reported that the bones of
P-depleted Atlantic salmon were extremely pliable especially opercula and ribs. Scoliosis was observed frequently,
but there was no incidence of fractures. Shimeno et al. (1994) studied effects of dietary P supplementation on
perform ance and body compositions of juvenile yellowtail. In a 40-day feeding trial, fish growth, feed effi ciency
and PER were the highest when fish meal-based diet was supplemented with KH 2PO 4 at a 1.5% level (0.34% as P).
The dietary P level, however, had little effect on the whole body ash content. The amount of soluble P in diets
increas ed as the supplemental level of KH 2PO 4 increased. Thus, the percentages of water-soluble P per total P
were more than 50% in diets high in P. However, the apparent digestibility of P in such diets was only about
13-33%. El-Zibdeh et al (1995a) estimated the dietary P requirement of redlip mullet Liza hematochiela. Fish
grew from 3.8 to 44 g (max) in a 14-wk feeding trial and from 27 to 154 g (max) in another trial lasted for 12 weeks.
Dietary P (total P) requirement estimated based on the maximum weight gain was between 0.37 and 0.54% in the
first trial and between 0.56 and 0.71% in the second trial. Feed efficiencies were about 91% and 61% in the first
and second trials, respectively. The authors made numerous other measurements including feed intake,
hepatosomatic index, condition factor, blood analyses (hematocrit, hemoglobin, total protein, triglycerides, total
cholesterol, Ca, P), vertebral analyses (lipids, ash, Ca, P, Cu, Zn, Mn, Mg, Fe), and liver analyses (moisture, lipids,
protein, ash). Interpretations of the data are, however, diffi cult. For example, P content in vertebrae increased
proportionally to the dietary P intake (no plateau) in the first trial. In the second trial, fish consumed a diet of the
lowest P had the highest P content in both serum and vertebrae. El-Zibdeh et al (1995b) studied dietary P
requirem ent for yellow croaker Nibea albi flora. Fish grew from 20 to 66 g (max) in a 14-wk feeding trial with the
feed effi ciency of about 86% (max). The estimated dietary P requirement based on the weight gain and feed
efficiency appears to be between 0.42 and 0.65% as total P, while the requirement estimate based on the blood serum
P is between 0.32 and 0.42% total P (authors interpreted the data otherwise). Elangovan & Shim (1998) reported
that dietary (total) P requirement for the maximum weight gain of juvenile tiger barb was 0.52% based on the broken
line analysis of the data. The diets had a feed efficiency of 0.55 (max.). The sources of dietary P were cas ein (basal
ingredient) and KH 2PO 4 (graded). Chavez-Sanchez et al. (2000) reported that dietary P requirement for an
American ci chlid, Cichlasoma urophthalmus, was 1.5g/kg diet (sic) for optimum growth. Dietary P levels
inversely correlated to the carcass fat content of the fish. The authors claimed that optimum Ca/P ratio was 1.3
when P was supplied from casein and KH 2PO 4 and CaCO 3, respectively. The initial mean body wt of the fish was
only 0.4 g, suggesting that the fish were fed micro-particulate diets. In this case, a leaching loss of P from the diet
should be considered significant. What the authors fed might be different from what the fish consumed as
discussed before (cf. Chapter of phospholipids). The effect of supplemental calcium might also be attributed to its
possible effect on reducing soluble P in the diet by forming less soluble calcium phosphates. Pimentel-Rodrigues
& Oliva-Teles (2001) fed juvenile sea bream (initial body wt, 5.1g) for 42 days with 7 diets of varied P
concentrations (0.37-1.5% total P). The feed efficiency of the normal to high-P diets were 0.92-1.02. Fish fed
low-P diets had lower growth rate, but the body P content did not differ from those consumed high-P diets. Vielma
© 2000, 2005. Shozo H. Sugiura. All rights reserved.
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