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Nitrogen metabolism and excretion in the mangrove killifish Rivulus marmoratus II. Significant ammonia volatilization in a teleost during air-exposure

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

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

View larger version (23K): [in a new window]   Fig. 1. Ammonia excretion (JAmm) (A) and urea excretion (JUrea) (B) in laboratory-reared Rivulus marmoratus before emersion and at 2 h intervals following 12 h of emersion. Statistical comparisons were performed between pre- and post-emersion excretion rates. For JUrea (B), comparisons were made at the appropriate time periods to take into consideration the diurnal pattern of JUrea (i.e. filled columns pre-emersion were compared with filled columns post-emersion). No significant differences were found between pre- and post-emersion JAmm or JUrea. Values are expressed as means + S.E.M. (N=18).

View larger version (19K): [in a new window]   Fig. 2. Ammonia excretion (JAmm) (A) and urea excretion (JUrea) (B) in air-exposed and submerged laboratory-reared Rivulus marmoratus. Values are expressed as means ± S.E.M. (N=6). FP, filter paper. For JAmm (A), values presented for total JAmm in air (volatilized+FP) are calculated from the mean of these two rates at each time period. For JUrea (B), excretion rates in air were significantly lower at all time points (P<0.05), and different letters indicate significant differences between time points (P<0.05).

View larger version (16K): [in a new window]   Fig. 3. Whole-body ammonia (A) and urea (B) levels in air-exposed and submerged laboratory-reared Rivulus marmoratus. Values are expressed as means ± S.E.M. (N=6). An asterisk denotes a significant difference from the corresponding control value.

View larger version (15K): [in a new window]   Fig. 4. Percentage of ammonia and urea excretion through the anterior and posterior regions of laboratory-reared Rivulus marmoratus in water (A) and in air (B). Values are expressed as means + S.E.M. (N=7). An asterisk denotes a significant difference between the anterior and posterior regions.