MILLIKIN: NUTRIENT REQUIREMENTS OF FISHES 



Since dietary protein quantity and quality are 

 major determinants of growth in fish, numerous 

 investigations have been conducted to determine 

 protein requirements for specific fish species. 

 Protein requirement studies that examine vari- 

 ous concentrations of dietary protein with higher 

 carbohydrate concentrations being substituted 

 for protein in lower protein diets often produce 

 reliable approximations of quantitative dietary 

 protein requirements (Table 2). However, accord- 



generally decrease with increasing age or fish 

 size. For example, salmonids require about 50% 

 protein" during the initial feeding stage of fry, 

 decreasing to 40% protein after 6 to 8 wk, with a 

 further reduction to 35% protein for yearlings 

 (National Research Council 1973). Channel cat- 

 fish fry require a minimum of 40% protein, de- 

 creasing to 30 to 36% for fingerlings and 25 to 

 30% protein for subadults weighing >114 g (Na- 

 tional Research Council 1977; Andrews 1977). 



Table 2.— Quantitative protein requirements of several fish species. 



'G = growth, FC = feed conversion, BP = body protein, PER = protein efficiency ratio. 

 2 Protein requirement increased from 40 to 45% as salinity increased from 10 to 20%o. 

 'Highest protein concentration examined. 



ing to Rumsey (1978), protein sources generally 

 have higher metabolizable energy values than 

 carbohydrate sources for salmonids. Thus, in 

 many dietary protein requirement studies, fishes 

 were probably offered higher metabolizable en- 

 ergy values in the high protein diets compared 

 with the low protein diets. Since fish fed low pro- 

 tein diets may have had less available energy, 

 additional protein may have been shunted for 

 metabolic requirements other than growth. 

 Many of the quantitative protein requirements, 

 listed in Table 2, may be overestimated values 

 due to this shift in utilization of protein in low 

 protein diets (Rumsey 1978). Therefore, protein- 

 energy studies examining several energy concen- 

 trations within each of several dietary protein 

 concentrations provide better estimates of quan- 

 titative dietary protein requirements of fishes. 

 Dietary protein concentration requirements 



The higher protein concentrations in these two 

 ranges produce better growth of channel catfish 

 fingerlings and subadults, whereas the lower 

 protein concentrations provide better protein 

 conversion (weight protein fed -r weight gain) 

 (Andrews 1977). 



Increased water temperature has variable 

 effects on the minimal protein or energy require- 

 ment for maximal growth rate of fishes. For ex- 

 ample, chinook salmon fingerlings require 40% 

 protein at 8°C and 55% protein at 15°C (DeLong 

 et al. 1958). Striped bass fingerlings (initial 

 mean weight = 1.4 g) require 47% protein at 

 20.5°C, while additional dietary protein is re- 

 quired (about 55%) at24.5°C for maximal growth 

 of slightly larger fingerlings (initial mean 



4 Nutrient content of diets is expressed as percentage of the 

 diet on a dry weight basis, unless otherwise noted. 



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