The relationship between Protein Source and Nitrogen Metabolism in the Trout

Abstract

Various experiments connected with the use of
novel proteins (SCP's) in fish diets are described. In
the first series of experiments classical nitrogen balance
techniques were used. From these, MFN was found to be
175 mg N/100g diet and EUN 12.37 mg N/100g fish/day.
Using this data, true NPU's were determined at various
levels of N intake ranging from 36 to 140 mg/100g fish/
day. True NPU decreased linearly as N intake increased,
the rate varying only slightly with protein source. For
herring meal (HM) these values were between 0.97 and 0.48,
the others being - petroyeast (PY) 1.0 - 0.67; bacterial
protein (MB) 0.71 - 0.48; algal protein (SA) 0.87 - 0.55;
and fungal protein 0.79 - 0.54. Apparent NPU was practically
constant regardless of N intake. A further experiment
showed that the decrease in true NPU was not ameliorated
by the use of high energy diets.
Growth experiments incorporating NPU determinations
by carcass analysis gave the following true digestibility
(%), true NPU, BV and PER values:- PY 91.6, 0.42, 0.46,
2.01; MB 93.5, 0.37, 0.40, 1.62; SA 83.1, 0.32, 0.38, 1.33;
HM 91.2, 0.38, 0.41, 1.91; soyabean (SY) 43.6, 0.18, 0.41;
brewers yeast (BY) 79.9, 0.30, 0.38, 1.17; casein (CS)
98.7, 0.40, 0.41, 1.97. Dietary effects on growth rate,
body composition and food intake were also noted. For
carp, the equivalent values were:- PY 96.6, 0.47, 0.49,
2.08; MB 95.5, 0.49, 0.52, 2.54; SA 87.1, 0.36, 0.41, 1.15;
HM 80.3, 0.64, 0.79, 2.82,; SY 83.7, 0.42, 0.5, 1.353
CS 93.0, 0.49, 0.52, 2.54. The results are discussed in
relation to the amino composition of the diets.
Food preference trials with demand feeders gave
inconclusive results as trigger preference was often
prevalent. Additional work on photoperiod and demand
feeding rhythm showed that trout at 12°C exhibit peaks
of feeding every 8 hours.

Date of Award	1979
Original language	English
Awarding Institution	Aston University