QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online May 13, 2004
Journal of Experimental Biology 207, 2011-2020 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00956

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in JEB Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Barimo, J. F. Articles by Walsh, P. J. Search for Related Content PubMed PubMed Citation Articles by Barimo, J. F. Articles by Walsh, P. J.

Dogmas and controversies in the handling of nitrogenous wastes: Ureotely and ammonia tolerance in early life stages of the gulf toadfish, Opsanus beta

John F. Barimo^1,*, Shelby L. Steele², Patricia A. Wright² and Patrick J. Walsh¹

¹ Division of Marine Biology and Fisheries, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149-1098, USA
² Department of Zoology, University of Guelph, Guelph, Ontario N1G 2W1, Canada

View larger version (25K): [in a new window]   Fig. 1. Map of South Florida and the Florida Keys depicting field locations in Florida Bay (FB-1) and Biscayne Bay (BB-1) where artificial habitats or shelters were deployed. The FB-1 site was used to document toadfish spawning activity and sample water for in situ nitrogen excretion within shelters. BB-1 was used to sample early life history stages of toadfish for OUC enzyme analysis and to harvest whole nests (shelter + adult + offspring) for experimental studies.

View larger version (15K): [in a new window]   Fig. 2. Urea-N and ammonia-N excretion rates for juvenile toadfish (N=7, 14–15 mm TL). Juveniles were reared from eggs collected in Biscayne Bay and were used within 1 week of full yolk-sac absorption. The percent of waste nitrogen expressed as urea-N (% ureotelic) appears above bar pairs at each 24 h sampling interval. Values are means + S.E.M.

View larger version (14K): [in a new window]   Fig. 3. A representative 26 h record of cumulative urea-N and ammonia-N from an individual juvenile toadfish (14 mm TL). Urea pulsing was noted in all juvenile toadfish tested (N=7) but the intensity and frequency of the pulse varied among individuals. This individual was collected as a fertilized egg in Biscayne Bay and was used within 1 week of full yolk-sac absorption. Note the urea pulse at 10–12 h and that the ammonia excretion rate was relatively constant.

View larger version (14K): [in a new window]   Fig. 4. Results of the ammonia 96-h LC50 test plotting survivorship of juvenile fish (<16 mm TL) against total ammonia-N concentration (N=30 for each treatment group). Juveniles were reared from eggs harvested in Biscayne Bay and were used within 1 week of full yolk-sac absorption. An arrow depicts the calculated LC50 value. The test was conducted in individual 2-litre chambers for each treatment group with a daily 50% water change, and ammonia concentrations were verified at t0 and at 24 h intervals thereafter.

View larger version (18K): [in a new window]   Fig. 5. Enzyme activities for glutamine synthetase (GSase), ornithine transcarbamylase (OTCase), arginase and carbamoyl phosphate synthetase III (CPSase III) measured in homogenized whole toadfish. Developmental stages presented are egg II (10–20 days post-fertilization), yolk-sac larvae I (1–7 days post-hatch), yolk-sac larvae II (8–14 days post-hatch) and juveniles (yolk-sac completely absorbed; <16 mm TL). Various developmental stages were collected in Biscayne Bay and flash frozen with liquid N2. Statistically different groupings (a–d) from one-way ANOVA post-hoc analysis are presented above bars for each ornithine–urea cycle enzyme group. Values are means + S.E.M., =0.05 and N=6 for each developmental stage. Note that CPSase III activity is expressed as nmol min–1 g–1 (y2 axis).

View larger version (17K): [in a new window]   Fig. 6. The proportion of CPSase II and CPSase III occurring in toadfish developmental stages, which include egg II (10–20 dayspost-fertilization), yolk-sac larvae I (1–7 days post-hatch), yolk-sac larvae II (8–14 days post-hatch) and juveniles (yolk-sac completely absorbed; <16 mm TL). Developmental stages were collected in Biscayne Bay and immediately frozen with liquid N2. Statistically different groupings (a–c) from one-way ANOVA post-hoc analysis are presented above bars for each group of developmental stages. Values are means + S.E.M., =0.05 and N=6 for each developmental stage.

View larger version (18K): [in a new window]   Fig. 7. Enzyme activities for glutamine synthetase (GSase), ornithine transcarbamylase (OTCase), arginase and carbamoyl phosphate synthetase III (CPSase III) were measured in juvenile toadfish exposed to 0, 500 and 1000 µmol N l–1 ammonia for 96 h. Data are presented as means + S.E.M. Juveniles were reared from eggs harvested in Biscayne Bay and were used within 1 week of yolk-sac absorption. OTCase was the only enzyme group with a significant difference (P<0.05) among ammonia treatments. The sample size was N=4 for all categories except for the OTCase control and 500 µmol N l–1 treatment (N=6). Statistically different groupings (a,b) from the one-way ANOVA post-hoc analysis are presented above bars for each OUC enzyme. Note that CPSase III activity is expressed as nmol min–1 g–1 (y2 axis).