Gonad Morphology, Histology, 

 and Spermatogenesis In 

 South Pacific Albacore Tuna 

 Thunnus alalunga (Scombridae) 



Frank J. Ratty 



Department of Biology, San Diego State University 

 San Diego, California 92182 



R. Michael Laurs 



Coastal Fishieries Resource Division, Soutfiwest Fisfieries Center 

 National Marine Fisheries Service, NOAA, PO Box 271 

 La Jolla, California 92038 



Raymond M. Kelly 



School of Medicine, M-OI I. University of California, San Diego 

 La Jolla, California 92093-001 I 



The reproductive biology of tuna, 

 and tlie albacore Thunnus alalunga 

 in particular, is not well understood 

 with respect to functional morphol- 

 ogy of the gonads in relation to sex- 

 ual maturity. In the course of an in- 

 vestigation of the genetic variability 

 of albacore, differences in morphol- 

 ogy were observed between the 

 right and left gonad of male and fe- 

 male fish and the size of the fat body 

 associated with the gonads. Histo- 

 logical examinations were made to 

 determine the relationship between 

 these morphological differences and 

 the reproductive state of the go- 

 nads. In this paper we report find- 

 ings made on gonad morphology, 

 histology, and spermatogenesis and 

 relate them to the reproductive biol- 

 ogy of this species. 



Materials and methods 



Albacore specimens were collected 

 onboard the U.S. NOAA RV Town- 

 send Cromwell and the New Zea- 

 land RV Ka.haroa during coopera- 

 tive studies conducted in 1986 and 

 1987 to investigate the biology/ecol- 

 ogy and fishery exploration of alba- 

 core tuna in the South Pacific Ocean 



(Laurs 198G, Laurs et al. 1987). The 

 fish were caught using standard al- 

 bacore troll-fishing methods (Dot- 

 son 1980). In addition, specimens 

 were collected during commercial 

 fishing operations conducted in 

 1987 by Japanese longline vessels. 

 Locations of specimen collection are 

 summarized in Table 1. 



Soon after the fish were caught, 

 fork lengths were measured to the 

 nearest millimeter and the gonads 

 and associated fat body were dis- 

 sected from each fish. The right and 

 left gonads were preserved sepa- 

 rately in 10% neutral buffered for- 

 malin. Histological preparations 

 were initiated by washing the tissue 

 in running water for 12 hours. An 

 American Optical T/P tissue pro- 

 cessor was used to dehydrate and 

 embed the tissue in paraplast. The 

 tissue was sectioned at 5 microns 

 and stained with Harris' hematox- 

 ylin followed by eosin counter stain 

 (Humason 1979, Gabe 1976). 



Each testis subsample histological 

 preparation was classified accord- 



Reference to trade names does not imply en- 

 dorsement by the National Marine Fisheries 

 Service, NOAA. 



ing to (a) estimates of the relative 

 abundances of spermatocytes, sper- 

 matids, and sperm; (b) sperm-duct 

 development; and (c) sexual matur- 

 ity. In addition, the cross-sectional 

 area of the medial section of each 

 testis was determined. Electron mi- 

 crographs were prepared of sperm, 

 which had been washed from the 

 sperm duct of selected testes with 

 physiological saline and fixed in 3% 

 gluteraldehyde in 0.1 M phosphate 

 buffer. 



Results 



We observed asymmetrical differ- 

 ences in the size of both ovaries and 

 testes and in the size of the fat body 

 associated with gonads from both 

 sexes offish. Histological examina- 

 tion showed that all stages of sex- 

 ual maturity were represented in 

 the specimens of testes, allowing us 

 to describe spermatogenesis. No 

 sexually mature ovaries were found, 

 limiting the results for females to 

 asymmetrical size differences. 



Number and size of fish 

 examined 



Gonads from 197 albacore were 

 examined histologically during the 

 study. Sex ratio was nearly 1:1, 

 with 106 males and 91 females. The 

 fish ranged in fork length (FL) from 

 50 to 101 cm. Over 90% of females 

 and over 80% of males were less 

 than 90 cm FL, the size at which 

 sexual maturity is believed to first 

 occur in female albacore (Ueyanagi 

 1955, Otsu and Uchida 1959, Otsu 

 and Hansen 1961). Length-frequen- 

 cy distributions of the fish examined 

 are given in Figure 1. 



Gonad general morphology 



As in most teleosts, the gonads in 

 male and female albacore are paired, 

 elongate organs, located in the dor- 

 sal portion of the body cavity. They 



Manuscript accepted 18 September 1989. 

 Fishery Bulletin, U.S. 88:207-216. 



207 



