The National Science Foundation's (NSF) Tokyo Office periodically receives and disseminates reports on research developments in Japan that are related to the Foundation's mission. NSF-sponsored researchers currently working in Japan prepare many of these reports. These reports present information for use by NSF program managers and policy makers; they are not statements of NSF policy. .
Ms.Heather J. Boyle, a Ph.D. candidate in the Scripps Institution of Oceanography, University of California, San Diego, prepared the following report. Ms. Boyle was a participant in the 1999 Monbusho Summer Program sponsored by NSF and the Ministry of Education, Science, Sports and Culture (Monbusho). Professor Atsushi Ishimatsu of the Department of Marine Zoology, Faculty of Fisheries, Nagasaki University, Japan, hosted Ms. Boyle. Ms. Boyle can be reached via email at: hboyle58@hotmail.com
The Oxudercinae is a monophyletic subfamily of the gobiid family of fishes. The genera included in this subfamily run the evolutionary gamut from the pleisomorphic state of water breathing to the apomorphic state of air breathing (Murdy, 1989). The most highly-derived genera within the subfamily are the mudskippers: Periophthalmus, Periophthalmodon, Boleophthalmus, and Scartelaos (Murdy, 1989; Graham, 1997). These genera comprise a clade of amphibious air breathers, or fishes that breathe air when emersed (Yoshiyama and Cech, 1994; Graham, 1997).
Oxudercine fishes occupy habitats in which they are frequently exposed to air; they are found in mudflats, mangrove swamps, and along rocky coastlines in the Indo-West Pacific and West Africa (Springer, 1982; Murdy, 1989; Graham, 1997). In addition to the inter-tidal habitats in which they routinely move about, mudskippers spend time in burrows filled with hypoxic water (Gordon et al., 1968; Murdy, 1989; Ishimatsu et al., 1999).
There are three oxudercine species commonly found in Japan: Periophthalmus modestus, Boleophthalmus pectinirostris, and Apocryptodon punctatus. I was fortunate to have arrived in Japan during the spawning season of P. modestus. I began my summer's work at the Marine Research Institute, Nagasaki University, Nagasaki, with a week spent in Ashikari City, on the Ariake Sea. There are large expanses of tidal mudflats near Ashikari City, inhabited by the mudskipper species P. modestus and B. pectinirostris. During this time, I was able to assist my Japanese colleagues, Dr. Atsushi Ishimatsu, Dr. Tatsusuke Takeda, Naoko Itoki, and Daina Morekawa, in their observations of P. modestus mating behavior and parental care of eggs. These observations included video recordings of the mating activities of P. modestus on the surface of the mudflats and around the mouths of their burrows, as well as the placement of an endoscope into the brooding chamber of a P. modestus burrow. The endoscope made possible the observation of male P. modestus parental care of eggs. In addition to observations of adult P. modestus, eggs and larvae of these fishes were collected.
Soon after our return to the laboratory, a trip to the mudflats of Ariake Town, in Saga Prefecture, resulted in the collection of five P. modestus brooding chambers containing live eggs, as well as adult P. modestus for studies of respiratory physiology. My advisor from Scripps Institution of Oceanography, Dr. Jeffrey Graham, also joined us at this time and assisted in the work. The egg chambers were incubated under controlled conditions in the laboratory for ten days. During this time, five types of experiments were performed in order to determine the viability of eggs over time, the effects of osmolality, hyperoxia, and hypoxia on hatching, and the ability of larvae to survive under hypoxic conditions similar to those found in the P. modestus burrow and brooding chamber. These experiments were later repeated with five additional P.modestus brooding chambers containing live eggs.
In addition to studies of egg hatching and larvae survivability, studies of the respiratory physiology of P. modestus, B. pectinirostris, Apocryptodon punctatus, and Taenioides rubicundus were conducted. Measurements of the volume of the buccal chambers of specimens of each of these fishes were made and compared to body mass. The buccal chambers of these fishes function in air breathing (Graham, 1997); comparisons of buccal chamber volume and body mass thus contribute to an understanding of the degree to which each of these species is adapted for air breathing. Also, flow-through respirometers were used to determine both aerial and aquatic oxygen uptake rates during rest and immediately after exercise for specimens of P. modestus and B. pectinirostris. The objective of these experiments, which will be ongoing at the Marine Research Institute, Nagasaki University, and Scripps Institution of Oceanography, University of California, San Diego, is to determine if the mudskippers P. modestus and B. pectinirostris recover from exercise in air or in water. Measurements of the degree to which the oxygen debt incurred during exercise is repaid in air and water will allow the determination of the abilities of these fishes to recover in air and water after exercise.
The work begun this summer as a collaboration between the Marine Research Institute, Nagasaki University, and Scripps Institution of Oceanography, University of California, San Diego, will be ongoing. Observations of P. modestus mating behavior, egg development, parental care, and hatching will continue during the spawning season of 2000 at the Marine Research Institute, Nagasaki University. Respiratory physiology experiments will continue in the fall of 1999. Dr. Graham and I will travel to Townsville, Australia, in September. There we will collect specimens of the seven endemic oxudercine species and continue measurements of buccal volumes and respirometry work. The measurements of aerial and aquatic oxygen uptake rates will also continue at the two collaborating institutions.
Literature Cited
Gordon, M.S., Boetius, J., Evans, D.H., Oglesby, L.C. 1968. Additional observations on the natural history of the mudskipper, Periophthalmus sobrinus. Copeia. 4:853-857.
Graham, J.B. 1997. Air-Breathing Fishes. San Diego, Academic Press, 299 pp.
Ishimatsu, A., Aguilar, N.M., Ogawa, K., Hishida, Y., Takeda, T., Oikawa, S., Kanda, T., Huat, K.K. 1999. Arterial blood gas levels and cardiovascular function during varying environmental conditions in a mudskipper, Periophthalmodon schlosseri. J. Exp. Biol. 202:1753-1762.
Murdy, E.O. 1989. A taxonomic revision and cladistic analysis of the oxudercine gobies (Gobiidae; Oxudercinae). Rec. Australian Museum. Supplement 11:1-93.
Springer, V.G. 1982. Pacific plate biogeography, with special reference to shorefishes. Smithsonian Contributions to Zool. 367: 1-182.
Yoshiyama, R.M., Cech, J.J., Jr. 1994. Aerial respiration by rocky inter-tidal fishes of California and Oregon. Copeia. 1:153-158.