chemicals  was  developed.  This  so-called  medaka  specific- locus test system has led to more mechanistic studies. Suc- cess  in  detecting  AP-PCR/RAPD  polymorphisms  between two inbred strains, one established from the northern popu- lation of the Japanese wild medaka and the other from the southern population, allowed these researchers to generate a draft linkage map. This preliminary map will be followed by  a  more  definitive  one  (see  Shima  and  Shimada,  this issue). In 1999, the Environmental Agency of Japan listed the Japanese  medaka  as  an  endangered  species.  Wild  popula- tions  of  medaka  in  Japan  have  been  reduced  by  loss  of habitat,  including  irrigation  canals,  swamps,  marshes,  and ponds.  At  present,  conservation  of  the  species  tends  to  be ignored.  Shima  and  his  colleagues  are  convinced  that  the development of the medaka as a new model animal should parallel  the  scientifically  sound  preservation  and  mainte- nance  of  the  species  and  its  strains.  At  least  10  specimens each from nearly all wild medaka populations in Japan are being  archived  and  preserved  in  100%  ethanol  as  DNA specimens. Services The  current  stock  resources  of  Japanese  medaka  in- clude the following ones: Fourteen northern Japanese popu- lations; 54 southern Japanese populations; 5 hybrid popu- lations; 6 Chinese and Korean populations; 2 tester strains; 22  induced  specific-locus  mutant  strains;  and  2  congenic strains.  If  the  requested  numbers  of  embryos  or  fish  are available, they are distributed to researchers as long as the stocks  are  clearly  used  only  for  academic  purposes  and proper credit for their origin is given in publications. Contacts Dr.  Akihiro  Shima:  shima@biol.s.u-tokyo.ac.jp;  De- partment  of  Integrated  Biosciences,  Graduate  School  of Frontier  Sciences,  The  University  of  Tokyo,  Tokyo,  Japan 113-0033.  Dr.  Atsuko  Shimada,  Department  of  Biological Sciences,  School  of  Science,  The  University  of  Tokyo,  To- kyo, Japan 113-0033. Dr. Kenjiro Ozato, Yuko Wakamatsu, Laboratory  of  Freshwater  Fish  Stocks,  Nagoya  University Bioscience Center, Nagoya, Japan 464-8601; telephone and fax +81 3 5802 2911. AQUATIC  RESOURCES  AT  THE  UNIVERSITY OF  GEORGIA Program  Description Transgenic  Japanese  medaka  (Oryzias  latipes)  and  mum- michog  (Fundulus  heteroclitus)  are  new  research  resources available  at  the  Warnell  School  of  Forest  Resources,  Uni- versity  of  Georgia  (Winn  et  al.,  2000,  this  issue).  These transgenic fish were developed to improve methods used to assess  the  health  risks  of  exposure  to  chemicals  in  aquatic environments and to provide new animal models to study comparative in vivo mutagenesis. The transgenic fish carry prokaryotic vectors, bacteriophage lambda LIZ, or plasmid pUR288,  harboring  the  mutational  target  genes  (e.g., lambda lacI, lambda cII or LacZ) that are identical to those employed  in  transgenic  rodents.  Using  similar  mutation assay  procedures,  the  target  genes  are  separated  from  the fish genomic DNA and transferred into specialized bacterial host cells to quantify spontaneous and induced mutations. Many  fundamental  parameters  of  mutagenesis  are similar in transgenic rodents and fish. Spontaneous mutant frequencies  are  low  in  the  fish  models,  comparable  to  the ranges in transgenic rodents, which facilitates sensitive de- tection  of  mutations.  Exposing  fish  to  different  chemical mutagens  has  demonstrated  that  their  mutational  targets respond in a manner consistent with known mechanisms of mutagen  action  resulting  in  concentration-dependent,  tis- sue-specific,  and  time-dependent  mutations.  Spontaneous and induced mutational spectra in the fish also are consis- tent  with  those  of  transgenic  rodents.  Therefore,  in  vivo mutation analyses using transgenic fish are feasible and il- lustrate  the  potential  value  of  fish  as  comparative  animal models. The transgenic loci are genetically neutral, a feature that is advantageous compared to other assays such as those involving endogenous genes that may be limited to specific tissues  or  developmental  stages.  As  a  result,  mutations  in neutral transgenes accumulate and persist, avoiding the in- fluence  of  selective  pressures  in  vivo  on  mutational  fre- quency.  Recent  studies  in  rodents  indicate  that  some,  but not all potent genotoxins can be detected after a single acute treatment (Hoorn et al., 1993; Morrison and Ashby, 1994; Dolle et al., 1996). Consequently, the more treatments that are  given,  the  more  mutations  will  be  induced,  and  the more sensitive the test. The limitation here is that multiple doses can be more toxic than single doses, often requiring a compromise between number of treatments and the dosage. S242 William E. Hawkins et al. Next >>