NOAA Technical Memorandum NMFS 

JUNE 1981 

HISTOLOGICAL GONAD ANALYSES OF LATE SUMMER-EARLY WINTER 

COLLECTIONS OF BIGEYE TUNA, Thunnus obesus , AND 

YELLOWFIN TUNA, Thunnus albslcares , FROM THE NORTHWEST 

ATLANTIC AND THE GULF OF MEXICO 

Stephen R. Goldberg 

and 

Hillary Herring-Dyal 

4 

NOAA-TM-NMFS-SWFC- 1 4 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

Southwest Fisheries Center 
NOAA Technical Memorandum NMFS 

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JUNE 1981 

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. Goidberg 

and 

Hillary Herring-Dyal 

National Marine Fisheries Service 

Southwest Fisheries Center 

La Jolla, California 92038 

U.S. DEPARTMENT OF COMMERCE 

Malcolm Baldrige, Secretary 

National Oceanic and Atmospheric Administration Dr. John V. Byrne, Administrator 

National Marine Fisheries Service 

William H. Stevenson, Acting Assistant Administrator for Fisheries 
TABLE OF CONTENTS 

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 

METHODS . . . . . . . . . . . 

RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . 

DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . 

LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . 

Table 1 - Bigeye tuna: Histological Analysis Summary . . 

Table 2 - Yellowfin tuna: Histological Analysis Summary 

Figure 1 - Fishing areas . . . . . . . . . . . . . . . . 

Appendix A - Bigeye tuna: Statistical analysis summary . 

Appendix B - Yellowfin tuna: Statistical analysis summary 

Page 

1 

1 

2 

5 

6 

7 
Histological gonad analyses of 1 ate 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 

Whi ttier College 

Whi ttier, Cal i fornia 90608 

Hi 1 1 ary Herri ng-Dyal 

Southwest Fisheries Center 

National Marine Fisheries Service, NOAA 

La Jolla, 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. 

understanding of ye1 lowfin 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. 

In order to gain an 

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 Japanesf longline 

vessels fishing in the United States Fishery Conservation Zone. 

capture, fishes were weighed to the nearest kilogram and measured (forklength) to the nearest centimeter. A ventral longitudinal incision was made 

on the abgomen and the paired gonads were removed and placed in a 10% formal in 

solution. Formal i n-preserved gonads were weighe to the nearest gram. A 

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

Upon 

'Samples were obtained from the National Marine Fisheries Service, 

Southeast Fisheries Center, Miami , F1 orida. 

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

with a razor blade. 

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

This will facilitate penetration of the fixative. n ' 

U.S. Government. 

The use of trade names does not imply endorsement by the 
-2- 

cut at8 mm on a rotary microtome, mounted on slides and stained with iron 

hematoxylin followed by an eosin counterstain. All gonads were histologically 

classified according to their reproductive stages (Tables 1-2). 

weights, gonosomatic indices and statistical analysis for bigeye and ye1 lowfin 

tuna specimens are given in Appendix A and B respectively. 

Gonad 

RESULTS 

Females -- Ovaries of a1 1 femal es ( col lected August through February) 

were regressed (Tables 1-21 and consisted of primary oocytes arranged along 

connective tissue septa. There was no vacuolization which typically occurs 

prior to the beginning of yolk deposition for a new spawning cycle. 

almost total absence of follicular atresia, a process in which follicles 

undergo degeneration, suggests the ovaries had been reproductively inactive 

for several months. 

close of the reproductive season when follicles that initiated but did not 

complete yolk disposition, degenerate. Follicles in various states of 

atresia remain for some time after reproduction ceases. 

Also, the 

Foll icul ar atresia reaches its highest 1 eve1 s toward the 

Males -- Testes (collected August through February) were primarily 

regrem(Tab1es 1-2) as one would expect during a time when no spawning was 

occurring in the population. There were masses of residual sperm left in 

several males as is typical in regressed testes. In other cases, limited 

spermatogenesis was in progress. 

of sperm formation in males when females are reproductively inactive. 

However, the level of sperm formation was greatly reduced from what one would 

have expected during peak spermatogenesis. 

It is not unusual to find small quantities 

DISCUSSION 

Although yellowfin tuna and bigeye tuna are reported to spawn most of the 

year in tropical areas (Yuen, 1955; Yuen and June, 1957) we found no evidence 

of spawning activity during August through February for yellowfin tuna and 

September through February for bigeye tuna sampled from the populations under 

study. Furthermore, the lack of follicular atresia in females during February through September indicates they had not been spawning during the previous 6-8 

weeks. 

Prior to the onset of spawning, there is typically an increase in oocyte 

This was not 

size with a concomitant appearance of vacuoles. 

histological development to occur 8-10 weeks prior to spawning. observed in the samples of either species from December through February and 

would push the postulated onset of spawning to April through May at the 

earl i est. 

One would expect this 

It thus appears based gn these data, that the populations under study undergo a brief spring spawning period similar to that of northern fishes 

(Quasim, 1956) which have a restricted spawning season. In order to test our 

hypothesis of a postulated spring spawning period, it will be necessary to 

obtain additional female gonads from the period March through June. These 

addi tional gonads woul d be of particul ar interest in obtaining other Val uabl e 

information regardless of the reproductive state. Assuming that spawning femal es were obtained , we coul d then cal cul ate fecundi ty estimates, minimum 

size at sexual maturity, plot a seasonal gonosomatic index graph and obtain 

A 
-3- 

information as to the kind of spawning cycle the populations undergo. For 

example, are one or two modes of eggs spawned or is a mode of eggs matured and 

gradual ly released? If the specimens were reproductively inactive this 

information would be of interest and perhaps indicate the populations were 

transitory and migrated into the area after spawning elsewhere. Other 

factors, such as the possible existence of inadequate nutrition to permit 

spawning in the study areas and the possibility of environmental pollution 

inhibiting reproduction, need examining. 

answered by additional collections, especially of spring specimens. 

These are questions that can only be 

c 
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LITERATURE CITED 

Orange, C.J. 1961. Spawning of yellowfin tuna and skipjack in the 

eastern tropical Pacific as inferred from studies of gonad development. Inter-American Tropical Tuna Commission V(6) :459-526. 

Schaefer, M.B., and C.J. Orange, 1956. Studies of the sexual development and spawning of ye1 lowfin tuna (Neothunnus macropterus) and 

skipjack (Katsuwonus pelamis) in three areas of the eastern Pacific 

Ocean, by exami nation-ads. Inter-American Tropical Tuna 

Commi ssion I ( 6 ) : 283-349. 

Quasim, S.Z. 1956. Time and duration of the spawning season in some 

marine teleosts in relation to their distribution. J. Cons. Int. 

Expl or. Mer. 21: 144-154. 

Yuen, H.S.H. 1955. Maturity and fecundity of bigeye tuna in the 

Pacific. U.S. Dept. of Interior, Fish & Wildlife Service, Special 

Scientific Report, Fisheries No. 150, 30 pp. 

Yuen, H.S.H., and F.C. June. 1957. Yellowfin tuna spawning in the 

central equatorial Pacific. U.S. Fish & Wil dl i fe Service, Fish. 

Bull. 57 ( 112) : 251-264) . 
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APPENDIX A. Sumnary of yellowfin tuna gonad data collected 9/78 through 

12/79 in the northwest Atlantic and Gulf of Mexico 

mean mean mean 

fish gonad gonad No 

Date Sex weight St* weight S?* indice S2* Samples 

EX 

n 

2 =($ 

X P 

- 

9/78 d 

9/78 9 

10178 d 

10178 9 

11/78 d 

11/78 9 

2/79 d 

2/79 9 

8/79 d 

8/79 9 

9/79 d 

9/79 9 

10/79 d 

10179 9 

11/79 d 

11/79 9 

12/79 d 

12/79 9 

TOTAL 

24 .O 

25 .O 

24.64 

20.00 

23.00 

- 

31.00 

19.00 

21.67 

37 .oo 

25.44 

- 

29.88 

23.75 

26.14 

- 

25.00 

1 .oo 67.50 

2.00 43 .OO 

- - 

0.55 57.89 

- 22.6 

1.58 41.02 

- 

3 .oo 152.37 

- 15.22 

0.88 51.16 

5.58 42.63 

0.38 50.66 

- - 

2.42 73.64 

1.65 11.55 

1.35 61.29 

- - 

5 .oo 58.02 

6.8 

8.9 

- 

3 30 

- 

8.49 

- 

28.90 

- 

13.48 

13.59 

4.72 

- 

13.22 

0.85 

9.49 

- 

13.82 

.28 

.17 

- 

.23 

.ll 

.16 

- 

.48 

0.39 

0.24 

0.15 

0.20 

- 

0.23 

0.05 

0.23 

- 

0.23 

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- 

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2 

2 

0 

44 

1 

5 

0 

3 

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5 

9 

0 

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4 

7 

0 

2 

106 

*S = variance 
-9- 

APPENDIX B. Summary of bigeye tuna gonad data collected 10178 through 

12/79 in the northwest Atlantic and Gulf of Mexico 

mean mean mean 

fish gonad gonad No 

Date Sex weight Si* weight Sf* indice S?!* Samples 

R 1 i =(# 

- 

n 

10178 d - - - - - - 0 

10178 Q 36.73 4.32 143.42 20.68 .34 .03 22 

11/78 d 58.44 5.12 37.14 3.72 .07 .01 9 

11/78 Q 54.16 2.64 215.64 18.88 .41 .03 18 

12/78 d 35.10 2.46 25.00 3.37 .08 .01 25 

- - - - - 0 

12/78 9 33.19 1.85 119.43 10.87 .33 .02 57 

9/79 d 

9/79 Q 33 .OO - 143.32 - .43 1 

10179 d - 0 

10179 Q 25.60 0.87 74.62 11.59 .29 .03 5 

11/79 d 20.75 4.03 16.46 2.05 .09 .02 4 

- - - - 

11/79 Q 30.88 3.36 120.78 20.37 .36 .05 8 

d - - - 0 12/79 - 

12/79 0 26.11 2.51 72.61 10.25 .28 .02 9 

TOTAL 158 

*S = variance