FISHERY BULLETIN: VOL. 70. NO. 2 



apparent that a release rate with ecological sig- 

 nificance would have to consider both branchial 

 and renal release. 



Since the only data available from which one 

 can calculate nitrogenous release rates for ma- 

 rine teleosts are for nearshore or bottom fish 

 such as the sculpin, the starry flounder, and the 

 blue sea perch (Wood, 1958) , the following work 

 was undertaken using significant pelagic species 

 in order to assess the importance of marine 

 teleosts as a source of ammonia, urea, and cre- 

 atine in the euphotic zone. 



METHODS 



Experiments with the northern anchovy, 

 Engraulis mordax, were conducted in August 

 1970, in the laboratories of the Fj'shery-Ocean- 

 ography Center, La Jolla, California. Between 

 experiments the fish were kept in a tank of flow- 

 ing seawater and, unless specified otherwise, 

 were fed frozen brine shrimp daily. For each 

 experiment ten fish were placed in a 32-liter 

 circular Plexiglas chamber similar to that de- 

 scribed by Lasker (1970). During the first ex- 

 periment the chamber was darkened and 24 °C 

 seawater flowed through it at a constant and de- 

 termined rate. Beginning at the time the fish 

 were introduced, effluent was sampled at 10-min 

 intervals for 40 min. The fish had not been 

 fed for 24 hr. For experiments 2 and 3 the 

 flowing system was not used. The chamber was 

 filled initially with seawater and during the ex- 

 periments was exposed to room light. The tem- 

 perature during experiment 2 was 24°C and 

 water samples were taken at 10-min intervals 

 for 40 min. The fish had been fed 30 min prior 

 to their placement in the chamber. The temper- 

 ature during experiment 3 was 21.5°C and water 

 samples were taken at 10-min intervals for 70 

 min. The fish had not been fed for 48 hr and 

 ju.st after the 30-min sampling, 2.49 g of frozen 

 brine shrimp were thawed and added to the 

 chamber (the first and second portions of ex- 

 periment 3 will be referred to as 3a and 3b). 

 An appropriate control was run to determine the 

 eff'ect of the brine shrimp on the ammonia, urea, 

 creatine, and total nitrogen concentrations. 



Ten fish from the group used for experiments 

 1 and 2 and the ten used for experiment 3 were 

 sacrificed for weight determinations. Wet 

 weight determinations were made after blotting 

 the specimens on filter paper, and dry weight 

 was determined after they had been dried at 

 60 °C for 96 hr. 



Experiments with the Peruvian anchovy, 

 Engraulis ringens, were conducted off" the coast 

 of Peru in April 1969, during the RV Thompson 

 cruise 36. The methods of collection were de- 

 scribed by Whitledge and Packard (1971). Re- 

 lease rates for urea and ammonia were deter- 

 mined for each of three fish in separate one-liter 

 volumes of 0.45/a m Millipore^ filtered seawater 

 at 15°C. Each experiment was run until the 

 animal died (approximately 90 min). 



Experiments with the jack mackerel, Tra- 

 churus symmetricus, were conducted off the coast 

 of California in July 1970, during a cruise of the 

 RV Alpha Helix for the Institute of Marine 

 Resources Food Chain Research Group. Of 

 three specimens caught with lure and line, two 

 were placed in a 42-liter Plexiglas deck tank 

 which was continually flushed with surface sea- 

 water, and the third, which had been injured 

 when caught, was sacrificed for a weight deter- 

 mination. After approximately 5 hr the fish 

 were transferred to a similar tank recently 

 cleaned and filled with 19°C surface seawater 

 which had been filtered through a 173 /um nylon 

 mesh. Samples for ammonia and urea analyses 

 were taken at the beginning and at the conclusion 

 of the experiment 2 hr later. The fish were kept 

 another 20 hr and released. 



For samples from the E. ringens experiments 

 ammonia was determined by a modified form 

 of Johnston's (1966) rubazoic acid method and 

 urea by a urease hydrolysis coupled with the 

 rubazoic acid method. In all other experiments 

 ammonia was determined by the phenolhypo- 

 chlorite method (Solorzano, 1969) and urea by 

 the urease method (McCarthy, 1970). All de- 

 terminations were made in duplicate immedi- 

 ately after each experiment. Creatine concen- 

 trations were measured using a fluorescent com- 

 plex with alkaline ninhydrin (Whitledge and 

 Dugdale, in press). Total nitrogen was deter- 

 mined with the ultraviolet oxidation technique 



396 



