Figure 17. — Plankton stationB occupied during cruises of the RV 

 Shoyo Maru in 1969-70. Solid triangles represent stations at 

 which AuxU larvae were collected. (Hayasi 1972.) 



may reflect sampling intensity rather than actual dis- 

 tribution of young Auxis. In waters adjacent to the gulf 

 extending from Cape Hatteras to Cuba and particultirly 

 in the Strait of Florida, larval Auxis have shown up in 

 collections made in February-March (Tibbo and 

 Beckett 1972) and in May-June and in August (Klawe 

 1961) indicating the possibility that spawning occurred 

 during these months in this region. 



3.17 Spawn 



The eggs of Auxis are pelagic. Rao (1964), who ex- 

 amined ovaries of A. t hazard from the Indian Ocean, 

 observed that ripe eggs flowed freely out of the ovaries 

 when slight pressure was applied on the abdomen. Fresh 

 ripe eggs were perfectly spherical, had a colorless 

 homogeneous yolk mass, and had an average diameter of 

 0.97 mm (range of 0.88-1.09 mm). Preserved eggs were 

 somewhat translucent and had an average diameter of 

 0.86 mm (range 0.78-0.98 mm). Each ripe egg contained 

 a fairly large, spherical, single oil globule which 

 averaged 0.22 mm (range 0.21-0.22 mm) in diameter. 



Like other scombrids, female Auxis do not extrude all 

 their ripe eggs during spawning. Microscopic examina- 

 tion by Yoshida and Nakamura (1965) of ovaries from 

 eight A. thazard and five A. rochei caught in Hawaiian 

 waters revealed that both species had eggs in various 

 stages of resorption. One specimen of A. thazard still 

 contained residual eggs in the lumen; their diameters 

 varied between 0.75 and 1.30 mm and averaged 1.08 

 mm. No free residual eggs were found in A. rochei. 

 Concerning primordial eggs, two size groups — one rang- 

 ing from 0.07 to 0.10 mm and the other from 0.17 to 0.22 

 mm in diameter — were noted in ovaries of A. thazard. In 

 A. rochei, there was only one group of primordial eggs 

 ranging from 0.07 to 0.08 mm in diameter. 



The development of eggs and larvae of Auxis has been 

 described for the two species from the Atlantic and 

 Pacific Oceans. Mayo (1973) successfully hatched eggs 

 of two species of Auxis collected from the Straits of 



Florida and described the growth, behavior, ecology, 

 and development of the larvae. In the Pacific, artificial 

 fertilization of eggs and subsequent rearing of larvae 

 were conducted by Japanese scientists and their results 

 have been briefly discussed in section 2.41. Harada, 

 Murata, and Miyashita (1973) and Ueyanagi et al. 

 (1973) published the results of these tuna-rearing ex- 

 periments in which fish in advanced stages of sexual 

 maturity were used. Of three conventional fishing 

 methods attempted, only purse seining proved effective 

 in capturing mature yellowfin and skipjack tunas and 

 set nets for collecting mature Auxis. 



The "dry method" was used to obtain mature eggs 

 and sperm. Mature eggs from ripe female Auxis general- 

 ly oozed out when pressure was applied to the abdomen; 

 therefore, no incision was necessary (Ueyanagi et al. 

 1973). The investigators then obtained mature males 

 and applied pressure on the abdomen to force the 

 sperm-bearing milt over the eggs. The mixture was gent- 

 ly stirred before any water was added. 



Collected and fertilized at sea, the eggs were then 

 transported to various laboratories to be hatched 

 (Ueyanagi et al. 1973). Fertilized eggs of Auxis were 

 transported to laboratories in 2-4 h on eight different oc- 

 casions. The mortality of the eggs, which were trans- 

 ported in plastic bags filled with oxygen-saturated 

 seawater, was negligible. The details of the success 

 obtained in fertilizing and rearing both A. thazard and 

 A. rochei follow. 



Auxis thazard 



Mature eggs of A. thazard caught at Mera, Shizuoka 

 Prefecture, were collected, fertilized, and successfully 

 hatched on five occasions between 15 July and 15 

 August 1971 (Ueyanagi et al. 1973). Larval rearing was 

 most successful on the first trial when survival lasted up 

 to 10 days. Newly hatched larvae emerged 25 h after fer- 

 tilization and measured 2.59 mm TL. Heavy mortality 

 usually occurred 4-5 days after hatching. 



At Kushimoto, Wakayama Prefecture, mature eggs 

 were collected, fertilized, and transported to the Marine 

 Laboratory of Kinki University on three occasions in 

 1972 (Harada, Murata, and Miyashita 1973; Ueyanagi 

 et al. 1973). The spherical, fertilized eggs were buoyant 

 and varied from 0.93 to 0.98 mm in diameter (Fig. 18). 

 Emerging 34-62 h after fertilization at temperature 

 ranging between 21.4° and 23.5°C, the newly hatched 

 larvae measured from 3.26 to 3.60 mm TL. On the third 

 day after hatching, the larvae were fed rotifers, which 

 were replaced by marine plankton, mainly copepods, on 

 the seventh day. Twenty days after hatching, the larvae 

 were fed several types of fish flesh. The larvae were 

 placed in various-sized aquaria to determine the effects 

 of tank capacity on growth and survival; the investi- 

 gators found that growth was rapid in the 0.5-ton (500 

 liter) aquarium during the first 30 days after which time 

 the rate slowed appreciably (Table 11, Fig. 19). Max- 

 imum survival was 36 days. Larvae reared in aquaria 

 which had capacities of 3 tons (3,000 liters) and 70 tons 



22 



