The relative solubility, stability, and absorptivity of lutein and @-carotene were determined in 18 organic solvents. The solubility of both carotenoids was greatest in tetrahydrofuran, while hexane exhibited the least solubility for lutein; methanol and acetonitrile exhibited the least solubility for @-carotene. Stability was monitored for 10 days at room temperature by measuring absorbance changes at the wavelength maximum. In the majority of the solvents, initial absorbance decreased by less than 10% during the 10-day period. Degradation was greatest for both carotenoids in cyclohexanone. The relative absorptivities were determined by calculating the carotenoid concentration in a reference solvent using a reference absorptivity, and then Beer's Law was applied to the measured absorbance of the same carotenoid concentration in other organic solvents. Absorbance maxima and relative absorptivities were in good agreement with available literature values.

Two experiments were conducted to determine the effects of phytase on growth, apparent phosphorus (P), calcium (Ca), iron (Fe), zinc (Zn), magnesium (Mg), and copper (Cu) absorption, and apparent protein digestibility by striped bass Morone saxatills fed a high phytate diet. In experiment one, four diets with graded levels of phytase supplementation, 0, 500, 1,000, and 2,000 phytase units/kg of diet (PUkg), and a diet supplemented with inorganic P (positive control, total P, 0.73%; phytin P, 0.35%) were assigned to duplicate tanks, and were fed to fingerling striped bass for 16 wk. A digestibility trial was conducted at weeks 16-18, using 0.5% Cr20J as an indigestible marker in the diets. Phytase was sprayed post-extrusion on the basal diet (P-total, 0.58%; P-phytin, 0.35%). Experiment two consisted of a 2-wk digestibility trial with three treatments: 0 (basal; total P, 0.73%; phytin P, 0.34%), 1,000, and 2,000 PUkg, assigned to four, three and three replicate tanks respectively. Each tank contained an average of 20 striped bass (mean weight: 400 9). The diet used was similar to the basal in experiment one, which was modified to have low essential trace mineral concentrations, in order to increase the sensitivity of the assay. In experiment one, significant improvements (P 5 0.05) in growth, feed conversion ratios, and vertebral and scale ash concentrations of fish at the end of the experiment were achieved with either added inorganic P or increasing phytase supplementations. Results from both digestibility trials indicated that P absorption was improved with the addition of at least 500 PUkg. Absorptions of Ca and Fe were significantly increased (P 5 0.05) and Zn absorption marginally improved (P 5 0.06) when at least 2,000 PUkg was supplemented to the diet. Protein digestibility, Mg and Cu absorption were not significantly different in any treatment. Whole carcass P retention was significantly improved with the addition of 1,OOO PUkg, and 2,000 PUkg, when compared to fish fed the basal diet, 500 PUkg and positive control treatments. Results from these experiments indicate that phytase supplementation of at least 1,OOO PUkg is adequate to maintain growth rate and health comparable to an inorganic P supplemented diet. In addition, bioavailability and utilization of P is increased with increasing phytase supplementation. Diet supplementation of 2,000 PUkg increased Ca, Fe, and Zn digestibility by striped bass fed a high phytate diet.Feed costs in aquaculture operations account for approximately 50% of total operational costs (Ratafia 1994). It is, there-fore, critical that future research on fish feed for cultured species will find ways to reduce these costs and enable increased nutrient utilization of the diets. Currently most practical fish feeds for carnivorous fish,

Three experiments were performed in singlepass, flow-through systems to determine the dietary phosphorus requirement of striped bass Morone saxatilis. In Experiment 1, three semi-purified diets were formulated to contain 0.20,0.40, or 0.60% total phosphorus (entirely from animal protein) and were fed to striped bass having an average initial weight of 321 g. After 14 wk of feeding, significant differences in bone and scale mineralization were found among treatment groups. At a level of 0.40% dietary phosphorus there was a significant improvement of serum calcium (Ca) and tissue mineralization. In Experiment 2, five diets were formulated with graded levels of monopotnssium phosphate to yield total phosphorus levels of 0.15 (no P supplementation), 0.35,0.55,0.75, and 0.95% and fed to juvenile striped bass initially weighing an average of 7.9 g. After 6 wk, significant improvement in scale and vertebral mineralization occurred when fish were fed diets containing at least 0.55% phosphorus. Improvements were observed in growth, serum phosphorus, incidence of scoliosis, survival, and feed efficiency when the diet contained at least 035% P. In Experiment 3, the dietary phosphorus levels fed were 0.30, 038, 0.46, 0.54, and 0.62% total phosphorus using graded levels of monopotassium phosphate. Diets were fed to striped bass fingerlings initially weighing an average of 48 g. After 10 wk, significant improvement in scale, vertebral, and dorsal fin mineralization was observed when dietary phosphorus was at least 0.46%. A summary of the broken-line regression analyses of the data from these experiments indicated that the average total dietary phosphorus level required for optimal growth and mineralization of striped bass was 0.58%. Phosphorus (P) is considered to be the most limiting nutrient for plant and algal growth in freshwater estuaries. When algae die, oxygen in the water is reduced due to degradative reactions associated with the resulting dry matter. This often results in severe oxygen depletion of the water. A level of 10-30 hg/L phosphate P has been reported for unpolluted lakes (U.S. EPA 1976). The latter is considerably below values observed in some intensive fish culture systems. The excessive P content of many com-

Vitamin D is a complex of secosteroids that must undergo metabolic alterations to reach optimal biological activity. The parent compounds 1) ergocalciferol (D2) and 2) cholecalciferol (D3) can be synthesized in the leaves of many plants or in the skin of most animals, respectively. Transport of vitamin D steroids after absorption is associated with vitamin D binding proteins (DBP). In general, the relative binding affinities of the vitamin D steroids are: 25-hydroxy vitamin D3 [25-(OH)D3] = 24,25-dihydroxy vitamin D3 [24,25-(OH)2D3] = 25,26-dihydroxy vitamin D3 [25,26-(OH)2D3] > 25-hydroxy vitamin D2 (25-(OH)D2) > 1,25-dihydroxy vitamin D3 [1,25-(OH)2D3] > vitamin D3. The DBP in poultry does not bind D2 forms effectively, and therefore poultry can not use this form of vitamin D adequately. The concentration of 25-(OH)D3 in blood seems to be well correlated with dietary vitamin D intake or exposure to ultraviolet light. The 1 alpha hydroxylase enzyme in the kidney is subject to negative feedback regulation and is critical for formation of the active metabolite 1,25-(OH)2D3. The intracellular vitamin D receptor (VDR) specifically binds 1,25-(OH)2D3 and is necessary for cellular action. Increased levels of two to three orders of magnitude are required for 25-(OH)D3 to compete with 1,25-(OH)2D3 for binding on VDR. Feeding studies with 25-(OH)D3 suggest it has nearly twice the activity of vitamin D3. Hatchability studies have shown that 25-(OH)D3 supports good fertility and hatchability, whereas hens fed only 1,25-(OH)2D3 did not have normal hatchability. Likewise, 1,25-(OH)2D3 seems to reach toxic levels at dietary concentrations only two to three times optimal dietary levels whereas feeding 25-(OH)D3 for extended periods at levels 8 to 10 times requirement seems to have no adverse effects. It seems that 25-(OH)D3 is the most active metabolite of vitamin D3, ultimately capable of supporting both cellular functions and embryonic development in chickens and turkeys when fed as the sole source of vitamin D3.

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