MP13 Aquatic Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(KAJ-1117-828487) High ambient ammonia promotes growth in a ureogenic goby, Mugilogobius abei.

Kajimura, Makiko^{1, 3}, Iwata, Katsuya ¹, Sakamoto, Tatsuya ², Iwata, Ichiko ¹, Nishiguchi, Eri¹, Smith, Richard ³, Wood, Chris ³, ¹ Biological Laboratory, Faculty of Education, Wakayama University, Wakayama, Wakayama, Japan³ Department of Biology McMaster University, Hamilton, Ontario, Canada² Ushimado Marine Laboratory, Okayama University, Setouchi, Okayama, Japan

ABSTRACT- While ammonia is generally viewed as a toxicant which inhibits growth during sublethal exposure, recent reports in salmonids suggest that chronic, very low level exposure may actually promote growth. Mugilogobius abei lives naturally in elevated ammonia environments and has the ability to produce large amounts of urea under these conditions. Despite this metabolically costly approach, M. abei exposed to high levels of ammonia (2mM NH₄Cl, pH=7.5-8.0) in a pilot experiment exhibited no adverse effects on growth. To further investigate this observation the growth of M. abei was measured at room temperature for 8 weeks at a constant ration level under solitary and grouped conditions, in 20% SW with or without (control) 2mM NH₄Cl (pH = 7.5-8.0). Furthermore, pituitary mRNA levels of growth hormone, oxygen consumption, incorporation of external ¹⁵N-ammonia into amino acid and protein fractions as well as behavioral activities were also examined. The specific growth rates of ammonia-exposed fish under grouped condition over the 8 weeks were significantly higher than those of control, while those rates under solitary condition were not significantly different between the treatments. The pituitary of ammonia-exposed fish had higher growth hormone mRNA than in control fish. The use of ¹⁵N isotope revealed that M. abei can actively use external ammonia as a supplementary nitrogen source. Oxygen consumption of ammonia-exposed fish was significantly lower than that of control fish. Locomotor activity and aggressive behavior under grouped condition were significantly reduced in ammonia-exposed fish as compared those of control. These combined alterations in the ammonia-exposed fish may result in the higher growth rates. We are currently measuring the protein synthesis rates of control and ammonia-exposed fish.

Key words: Ammonia, Growth promotion, Mugilogobius abei, Protein synthesis