Histological gonad analyses of late summer-early winter collections 



of bigeye tuna, Thunnus obesus , and yellowfin tuna Thunnus albacares , 



from the Northwest Atlantic and the Gulf of Mexico 



Stephen R. Goldberg 



Department of Biology 



Whittier College 



Whittier, California 90608 



Hillary Herri ng-Dyal 



Southwest Fisheries Center 



National Marine Fisheries Service, NOAA 



La J oil a, California 92038 



INTRODUCTION 



There is little information available on the reproduction of yellowfin 

 and bigeye tuna in the Gulf of Mexico and adjacent Northwest Atlantic Ocean. 

 Previous reproductive studies on samples from the Pacific Ocean (Schaefer and 

 Orange, 1956; Orange, 1961; Yuen, 1955; Yuen and June 1957) provide some 

 information on the spawning of these species. In order to gain an 

 understanding of yellowfin and bigeye tunas' reproductive potential, a 

 histological gonadal analysis was conducted. This analysis will contribute to 

 a more complete picture of the reproductive biology of yellowfin and bigeye 

 tunas. 



METHODS 



Specimens were collected from the Gulf of Mexico and the Northwest 

 Atlantic Ocean (Figure 1). The collections were made from September 1978 

 through December 1979 by United States observers aboard Japanese longline 

 vessels fishing in the United States Fishery Conservation Zone. Upon 

 capture, fishes were weighed to the nearest kilogram and measured (fork- 

 length) to the nearest centimeter. A ventral longitudinal incision was made 

 on the abdomen and the paired gonads were removed and placed in a 10% formalin 

 solution/ Formal in- preserved gonads were weighed to the nearest gram. A 

 sample from each gonad was embedded in Paraplast. Histological sections were 



^■Samples were obtained from the National Marine Fisheries Service, 

 Southeast Fisheries Center, Miami, Florida. 



^ Fixation in large gonads was not uniform. This problem can be 

 avoided in future samples by making a slit along the length of the gonad 

 with a razor blade. This will facilitate penetration of the fixative. 



^ The use of trade names does not imply endorsement by the 

 U.S. Government. 



