Observing that almost all fish >29 cm had high repro- 

 ductive indices, Yasui hypothesized that liver weight is 

 related to oogenesis and that it can be used as an indi- 

 cator of sexual maturity. 



In the Spanish trap net fishery located in and around 

 the Strait of Gibraltar, the size of A. rochei at first 

 spawning is 35 cm for the females and 36.5 cm for the 

 males (Rodriguez-Roda 1966). Rodriguez-Roda classi- 

 fied the testes and ovaries according to the develop- 

 mental stages as follows: 



I Immature 

 n Maturing 

 in Ripening 



rV Prespawning 

 V Spawning 

 VI Spent 



Rodriguez-Roda noted that in May, a large proportion 

 of the males and females were in stage III. In June- 

 August some showed development in stage FV, but by 

 September about one-third of the males and one-fourth 

 of the females sampled had gonads that apf)eared to be 

 spent (Table 8). Rodriguez-Roda noted that gonad clas- 

 sification based on gross characteristics such as he used 

 could lead to misleading conclusions; however, he indi- 

 cated that the relative gonad weight (gonad weight in 

 relation to body weight) tended to confirm his conclu- 

 sions. 



125 g, respectively. According to Rao, the smaller of the 

 two fish may "have been captured while in the act of 

 spawning since most of the ripe ova were already lost by 

 the time it was examined." 



3.16 Spawning 



Earlier, it was pointed out that although the plank- 

 tonic eggs and larvae of Auxis become displaced from 

 the area of spawning due to ocean currents, the dis- 

 placement is insignificant. Therefore, localities where 

 larvae of 3 mm or less occur probably represent actual 

 spawning sites. 



In the eastern tropical Pacific, Auxis larvae are the 

 most abundant among all the scombrid larvae collected. 

 Ahlstrom (1971) identified 1,563 out of 1,919 scombrid 

 larvae in the EASTROPAC collection as Auxia spp. 

 Based on this information and the distribution of the 

 catches of larval Auxis, Klawe (1963) observed that off 

 Baja California, spawning occurred in coastal waters 

 whereas to the south it appeared to be in more oceanic 

 waters away from continents or islands. The most north- 

 erly area of spawning appeared to be near Cedros Island 

 and at the head of the Gulf of California. To the south, 

 Klawe found the limit of spawning to be off Point Santa 

 Elena in Ecuador. He delimited the general area of 



Table 8. — Percentages of male and female Auxis rochei from the Spanish trap net fishery classified as I - 

 immature, II - maturing, HI - ripening, IV' - prespawning, V - spawning, and VI - spent in May-September 

 in 1958, 1961, 1963, and 1964 combined (Rodriguez-Roda 1966). 



3.13 Mating 



No information is available on the mating habits of 

 Auxis but, in general, it is believed that scombrids 

 release their sexual products directly into the water 

 without pairing of the male and female. The mechanism 

 which triggers the reproductive activity, i.e., spawning 

 and fertilization, is still unknown. 



3.14 Fertilization 

 Fertilization is external. 



3.15 Gonads 



The gonads of Auxis are paired, elongate organs 

 suspended from the dorsal wall of the body cavity by 

 lengthwise mesenteries. Rao (1964) described the 

 ovaries of i4. thazard in "spawn-ripe" condition as pink- 

 ish-pale yellow organs. Two samples of ovaries coming 

 from fish measuring 41.6 and 44.2 cm weighed 52 and 



occurrence by drawing a straight line from Point Santa 

 Elena to the intersection of lat. 10°N and long. 116''W 

 and from there to Cedros Island off Baja California. 



In the extreme eastern Pacific, A. thazard spawn 

 throughout the year, although in the northern region, it 

 may be restricted (Figs. 12, 13). This phenomenon of 

 seasonal spawning in the northern region of the eastern 

 Pacific may be similarly reflected in the most southern 

 region, but data are inadequate to confirm this. Data 

 from collections made off Cape Blanco indicated that 

 Auxis spawn off Costa Rica throughout the year but 

 peak spawning occurs in December- April (Table 9). 

 Klawe et al. (1970), however, observed that the period of 

 peak spawning of A. thazard may vary, because their 

 data suggested that larvae were more abundant in 

 August-November with a peak in October (Fig. 14). 

 They suggested that differences in spawning peak 

 between their samples and those examined earlier by 

 Klawe (1963) may be due to differences in sampling 

 locations within the general area, to environmental 

 changes, or other unknown causes. 



16 



