Fingerling rainbow troul Oncorhynchus mykiss with initial mean weights of 9 g (small fish) and 35 g (large fish) were fed diets adequate in all known nutrients except phosphorus (P). In two experiments, triplicate lots of rainbow trout were fed basal diets containing either 0.14 or 0.41% non-phytin P. with or without graded levels of supplemental P. Deficiency of P reduced growth, feed efficiency (weight gained/weight fed), bone ash, and whole-body ash contents. The requirement for non-phytin P by small trout for maximum growth and feed efficiency was not more than 0.41% of diet; the requirement by large trout was between 0.34 and 0.54% of diet. The requirement of non-phytin P for maximum bone ash development was about 0.51% of diet for small trout and more than 0.54% for large trout. Whole-body phosphorus content of small trout suggested a requirement above 0.51% but not more than 0.61% non-phytin phosphorus. Although an effect of si/e of trout on the requirement was not clearly demonstrated, these results show that trout required more dietary P for bone mineralization than for weight gain. The minimum dietary requirement for non-phytin P for bone mineralization was probably between 0.54 and 0.61% of diet. Discharges of P into effluent water increased significantly as trout were fed increasing levels of P. When trout were fed 0.61% available P, approximately 67% of P consumed was retained, and discharges of soluble P in effluents were 2.0 g P/kg weight gain or 1.8 g P/kg feed fed.

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Triplicate lots of young Atlantic salnon (Salmo salar) were fed a diet containing graded levels of supplemental inorganic phosphorus. The basal diet, containing mainly dehulled soybean meal and other plant materials, provided 40% crude protein, 0.7% phosphorus, 1.5% calcium, and 4,000 IU of supplemental cholecalciferol per kg of diet. Supplements of inorganic phosphorus significantly improved growth, feed utilization, and bone ash content. Inorganic phosphorus supplementation up to 0.6% of the diet increased growth rate and bone ash content; additions beyond this level had little further effect. This study suggests that when young salmon are fed diets containing 0.7% phosphorus from plant sources, the minimum requirement for supplemental inorganic phosphorus is approximately 0.6% of the diet.

Triplicate lots of fry of rainbow trout (Salmo gairdneri) were fed a basal diet (47% protein) containing 67% corn gluten meal with and without a mixture of essential amino acids. The composition of the mixture was based on the differences between the amino acid contents of corn gluten meal and trout eggs. Fry fed the basal diet without added essential amino acids gained little weight, suffered high mortality and had eroded caudal fins. Addition of the mixture of amino acids (lysine, arginine, histidine, isoleucine, threonine, valine and tryptophan) significantly improved weight gain and prevented nearly all mortality and fin erosion. Single deletions of the amino acids valine, tryptophan, threonine, histidine and isoleucine had no significant effect on weight gain but the deletion of lysine alone significantly reduced weight gain and caused fin erosion and mortality. Deletion of arginine reduced weight gain (P less than .05), but did not cause mortality or fin erosion. Feeding graded levels of each of these two amino acids showed that the minimum lysine requirement for maximum growth was about 6.1% of protein, and the minimum arginine requirement was between 5.4 and 5.9% of protein. The lysine requirements for prevention of fin erosion and mortality appeared to be lower than that for maximum weight gain.

Two experiments were conducted with rainbow trout Oncorhynchus mykiss to investigate the influence of several diets and supplemental phosphorus on discharges of phosphorus in hatchery effluent water. A diet was formulated to contain no fish meal and a reduced level of non‐phytin phosphorus (approximately 0.9%) provided, in part, by supplemental defluorinated rock phosphate, which has a low solubility in water. Feeding rainbow trout this diet supported 86% of the growth attained with a conventional hatchery diet while discharges of phosphorus in the effluents decreased by 40–51%.

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Previous researchers demonstrated that a mortality in fry (called Cayuga syndrome) of Atlantic salmon Salmo salar from Cayuga Lake (New York) was associated with low levels of thiamine. They reduced the mortality of fry by bathing or injecting fry with thiamine. We injected four to six gravid female Atlantic salmon with either physiological saline (PS) or PS plus thiamine (7 mg/kg weight) 14-23 d before eggs were stripped, fertilized, and incubated in individual lots. Chemical analyses showed that eggs from control and treated salmon contained 1.1 and 1.6 nmol thiamine/g, respectively. Thiamine injections had no significant effect on the percentage of eggs that hatched. Between 700 and 800 Celius degree-days postfertilization, control fry (saline) showed signs of Cayuga syndrome and a 45% incidence of mortality; in contrast, mortality was only 1.9% for fry that received thiamine. By 1,078 degree-days postfertilization, mean mortality of control fry was 98.6%, whereas that for thiamine-injected salmon was 2.1%. This study showed that thiamine injections of prespawning female salmon from Cayuga Lake increased thiamine content of their eggs and prevented the Cayuga syndrome and subsequent mortality of fry. Historically, overfishing, pollution, and building of dams and barriers to spawning migration were suggested as possible causes of the decline of the Atlantic salmon in Lake Ontario and Cayuga Lake. Based on our findings and other reports, we suggest another possible contributing cause of the extirpation of landlocked Atlantic salmon in Lake Ontario and some other inland waters of New York: the entrance of alewives Alosa pseudoharengus containing thiaminase, which induced thiamine deficiency in eggs and increased mortality in fry of the predatory salmon.Atlantic salmon Salmo salar, which were once

Fry of Atlantic salmon (Salmo salar) fed a diet containing isolated fish protein grew significantly faster than those fed a diet containing casein without supplemental amino acids, and had improved feed conversion and lower mortality. Supplementing the casein diet with essential amino acids to the levels in the isolated fish protein diet significantly increased growth rate, reduced mortality, and improved feed conversion.When fingerling rainbow trout (S. gairdneri) were fed diets containing soybean meal as the sole source of protein, additions of amino acids to simulate those levels of essential amino acids in trout eggs and isolated fish protein significantly improved growth. Additions of methionine, lysine, histidine, and leucine individually and in several combinations had no effect.