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Nitrogen metabolism and excretion in the mangrove killifish Rivulus marmoratus I. The influence of environmental salinity and external ammonia

N. T. Frick and P. A. Wright^*

Department of Zoology, University of Guelph, Guelph, Ontario, Canada N1G 2W1

View larger version (14K): [in a new window]   Fig. 1. Diurnal ammonia excretion (JAmm) (A) and urea excretion (JUrea) (B) in laboratory-reared Rivulus marmoratus. Values are expressed as means + S.E.M. (N=18). Columns labelled with one or more letters that are the same are not significantly different. Columns labelled with no letters in common are significantly different (P<0.05).

View larger version (21K): [in a new window]   Fig. 2. Diurnal ammonia excretion (JAmm) (A) and urea excretion (JUrea) (B) in wild-caught Rivulus marmoratus. Values are expressed as means + S.E.M. (N=14). Columns labelled with one or more letters that are the same are not significantly different. Columns labelled with no letters in common are significantly different (P<0.05).

View larger version (28K): [in a new window]   Fig. 3. Ammonia excretion (JAmm) (A) and urea excretion (JUrea) (B) in Rivulus marmoratus exposed to 0 (fresh water), 15 (control), 30 and 45  sea water for 1, 3, 5, 7 and 9 days. Values are expressed as means + S.E.M. (N=6). Columns labelled with one or more letters that are the same on a particular day are not significantly different; the absence of a letter indicates no significant difference. Columns labelled with no letters in common are significantly different (P<0.05).

View larger version (8K): [in a new window]   Fig. 4. Relationship between percentage urea excretion [JUrea/(JUrea+JAmm)], where JUrea is the rate urea excretion and JAmm is the rate of ammonia excretion, and external salinity in Rivulus marmoratus following 9 days of acclimation to each salinity; r2=0.92, y=–1.91x+13.01. Values are expressed as means ± S.E.M. (N=6).

View larger version (13K): [in a new window]   Fig. 5. Whole-body ammonia and urea levels in Rivulus marmoratus following 7 days of exposure to 0 (fresh water), 15 (control) and 45  sea water. Values are expressed as means + S.E.M., N=5 (45  treatment) or N=6 (0 and 15  treatment). Columns labelled with one or more letters that are the same are not significantly different; absence of a letter indicates no significant difference. Columns labelled with no letters in common are significantly different (P<0.05).

View larger version (18K): [in a new window]   Fig. 6. Urea excretion (JUrea) in Rivulus marmoratus exposed to 0–10 mmol l–1 NH4Cl in the external medium. Values are expressed as means ± S.E.M. (N=6). No statistical differences between treatments were found.

View larger version (16K): [in a new window]   Fig. 7. Whole-body ammonia (A) and urea (B) levels in Rivulus marmoratus exposed to 0 or 5 mmol l–1 NH4Cl for 10 days. Values are expressed as means + S.E.M. (N=5). An asterisk denotes a significant difference from the corresponding control value.