McCarthy and whitledge: nitrogen excretion 



of Armstrong, Williams, and Strickland (1966) 

 as described by Strickland and Parsons (1968), 

 but modified by the addition of sodium hypo- 

 chlorite (chlorine bleach, 5,25% active ingre- 

 dients) . One ml sodium hypochlorite per 100 ml 

 sample was found to increase the percentage of 

 conversion of creatine to nitrate. If added in 

 excess, the sodium hypochlorite will react with 

 the hydrogen peroxide to release oxygen. The 

 conversion of a standard solution of creatine to 

 nitrate in the digester was 43.4%, but the addi- 

 tion of sodium hypochlorite increased this val- 

 ue to 95.0%. Urea standards showed 96-100% 

 conversion without addition of sodium hypo- 

 chlorite. 



All chambers were washed with either fresh 

 or distilled water immediately prior to each ex- 

 periment and experimental periods were kept 

 to a minimum in an effort to reduce possible 

 effects of bacteria. Antibiotics interfere with 

 both of the ammonia methods mentioned above, 

 and could not be used to reduce bacterial ac- 

 tivity. Wood (1958) showed that in fish excre- 

 tion experiments running as long as 24 hr, bac- 

 teria on the surface of the fish do not affect 

 the results and the concentrations of released 

 nitrogen compounds were unchanged for an ad- 

 ditional 24 hr. 



The data were analyzed statistically using the 

 Mann Whitney U and the Tukey-Siegel tests 



to compare the medians and variabilities respec- 

 tively. Significant differences between exper- 

 iments were at the 0.05 level. 



RESULTS 



The release rates for ammonia, urea, creatine, 

 total nitrogen and the ammonia-urea ratios for 

 all experiments are given in Table 1. The re- 

 sults of the E. mordax experiments represent 

 the mean of the 10-min interval samples for 

 each experiment. An example of the data ob- 

 tained in one of these experiments is shown in 

 Figure 1. At the conclusion of the first E. mor- 

 dax experiment all of the fish had acquired dark- 

 ened dorsal coloration and one was locked into 

 the panic response described below for E. 

 ring ens. Immediately after release into the 

 large holding tank, food was added and all ex- 

 cept the one panicked fish, which died a few 

 hours later, fed normally and regained normal 

 coloration. During the other experiments with 

 E. mordax, the fish behaved normally and re- 

 tained their normal coloration. The fish in the 

 E. mordax experiment 3b were restricted from 

 feeding in their normal frenzied manner because 

 of the size of the chamber and at the con- 

 clusion a small portion of the food remained 

 uneaten. Creatine and total nitrogen values for 

 the second E. mordax experiment indicate that 



Table 1. — Excretion of nitrogenous compounds by Engraulis viordax, E. ringens, and 



Trachurus syimnetricus. 



397 



