NITROGEN EXCRETION BY ANCHOVY (ENGRAULIS MORDAX AND 

 E. RINGENS) AND JACK MACKEREL (TRACHURUS SYMMETRICUS)' 



James J. McCarthy^ and Terry E. Whitledge^ 



ABSTRACT 



Teleost fish have been shown to excrete a variety of nitrogenous substances among which 

 are ammonia, urea, and creatine. Previous reports show values for excretion of near- 

 shore or bottom fish but not of pelagic species. 



Two species of anchovy and jack mackerel were placed in chambers and their nitro- 

 genous excretion products were measured. Ammonia, urea, and creatine accounted for 

 82% of the total nitrogen excreted by Engraulis mordax and the identified fraction was 

 83% ammonia, 16%> urea, and 1% creatine. 



The significance of pelagic fish as a source of ammonia and urea in California coastal 

 waters is discussed. 



On the basis of the major end product of their 

 protein catabolism, animals are classified as am- 

 monotelic, ureotelic, and uricotelic. Although 

 these categories can be useful in evolutionary 

 considerations (Baldwin, 1964), they are some- 

 what arbitrary in that the excreta of most ani- 

 mals contain a mixture of ammonia, urea, and 

 uric acid. Mammals, elasmobranch fish, some 

 amphibians, and some reptiles are considered 

 to be ureotelic; teleost fish, some amphibians, 

 and most invertebrates are ammonotelic; and 

 birds and some reptiles are uricotelic (Baldwin, 

 1964). In ureotelic animals urea is produced 

 via the ornithine cycle. It is, however, unlikely 

 that this metabolic pathway is operative in non- 

 ureotelic organisms such as some teleosts, which 

 excrete substantial quantities of urea. Brown 

 and Cohen (1960) have shown that no marine 

 teleost has the enzymes necessary for the first 

 two steps in the ornithine cycle. The complete 

 complement of ornithine enzymes has been found 

 in the coelacanth however (Brown and Brown, 

 1967). 



Arginase is present in the livers of teleost 

 fish and hence dietary arginine has been sug- 



'■ Contribution #623 of the Department of Oceanog- 

 raphy, University of Washington, Seattle, WA 98105. 



^ Formerly at Scripps Institution of Oceanography, 

 La Jolla, California 92037; present address: 213 Ma- 

 caulay, Department of Earth and Planetary Sciences, 

 The Johns Hopkins University, Baltimore, MD 21218. 



^ Department of Oceanography, University of Wash- 

 ington, Seattle, WA 98105. 



gested as a source of urea (Hunter and Dauph- 

 inee, 1924-1925; Hunter, 1929), but this sug- 

 gestion is considered unlikely since arginine is 

 an essential amino acid for this group of or- 

 ganisms (Forster and Goldstein, 1969). Purine 

 catabolism also has been suggested as a means 

 of urea formation via uricolysis (Brunei, 1937), 

 and in support of this Goldstein and Forster 

 (1965) found uricolytic activity in the livers of 

 five species of marine and freshwater teleosts. 

 Delaunay (1929), Grafflin and Gould (1936), 

 Grollman (1929), and Smith (1929) determined 

 the composition of the urine of eight species of 

 marine teleosts and their results were summa- 

 rized by Scheer and Ramimurthi (1968). The 

 proportions of various components of the total 

 nonprotein urinary nitrogen varied greatly 

 within, as well as between, species (ammonia 

 varied from 0.5 to 9.6?f , urea varied from 0.1 

 to 30.8%, creatine varied from 6.5 to 61.7%, 

 and amino-N varied from 4.0 to 21.4%). In 

 1929 Smith used a divided chamber to permit 

 separate determinations of the nitrogen released 

 by the gills and by the kidneys, and his results 

 showed that essentially all of the ammonia and 

 urea released originated from the gills. In ad- 

 dition to these compounds, the branchial excreta 

 consisted of amine or amine oxide derivatives 

 while the less diffusible nitrogenous end products 

 such as creatine, creatinine, and uric acid were 

 excreted solely by the kidneys. It is therefore 



Manuscript accepted December 1971. 



FISHERY BULLETIN: VOL. 70, NO. 2, 1972. 



395 



