• • TOTAL LENGTH ^^ ^^^^^ j^^^^ 



O O WATER TEMP ^ " LAnt.lL iur«r3 



4 A WATER TEMP _i " 5"i"ll lAiMr 



DAYS AFTER HATCHING 



Figure 21. — Growth curves of Auxia rochei larvae reared in two 

 large (3,000 and 30,000 liter) and one small (500 liter) aquaria. 

 Length measurements are based on a single fish. (Harada, Mura- 

 U, and Furutani 1973.) 



a 3-ton aquarium and at age 2 days were fed rotifers and 

 marine plankton. By age 18 days, the larvae were 3 cm 

 long. From the 24th day, the larvae were fed minced fish 

 flesh, and they grew rapidly, reaching 5-6 cm by the 27th 

 day; however, heavy mortality reduced the number of 

 larvae to 36. By the 35th day, the survivors were 7.7-7.9 

 cm long. Only one larva survived for 50 days. The 

 Japanese investigators observed that this rate of growth 

 was slower than in previous experiments and believed 

 that it was due to lack of fish larvae as food. They em- 

 phasized, however, that the experiments succeeded in 

 artificially producing "seedlings" of A. rochei which 

 were several centimeters in length. 



In general, then, these experiments on frigate and bul- 

 let tunas have shown that: 



1. the eggs are buoyant, spherical, and measure 

 between 0.93 and 0.99 mm in diameter; 



2. the eggs hatch from 34 to 62 h after fertilization in 

 water temperatures ranging between 21.4° and 

 23.5°C; 



3. the newly hatched larvae measure 3.26 and 3.60 mm 

 TL; 



4. the larvae can be fed rotifers, copepods, and minced 

 fish flesh, in that order, after hatching; 



5. the growth and survival rates of larvae are better in 

 large rather than in small aquaria; and that 



6. under the best conditions, A. thazard larvae grew 120 

 mm in 33 days whereas A. rochei larvae grew 157 mm 

 in 52 days. 



3.2 Preadult phase 



3.21 Embryonic phase 

 See section 3.17 above. 



3.22 Larval phase 



Studies of anatomical development of larval Auxis 

 show that gross nucleation of the central nervous system 

 of young Auxis (3.6-23.0 mm SL) is similar to young 

 Thunnus albacares but heavier than in Katsuwonus 

 pelamis, T. obesus, T. thynnus, T. alalunga, T. atlan- 

 ticus, and Euthynnus alletteratus (Richards and Dove 

 1971). Using sectioned organs and tissues, Richards and 

 Dove determined that the swim bladder in katsuwonus 

 and Auxis, which, among scombrids is similar in the 

 very early stages of development, starts to degenerate 

 when the larvae reach the size of 9 mm, and is nearly 

 completely degenerated in specimens 24 mm long at 

 which time only the gas gland remains. Richards and 

 Dove also determined that in Auxis the kidney is short 

 until the larvae reach 11 mm after which it lengthens 

 significantly and that the postcardinal vein is larger in 

 Auxis and Euthynnus than in other species. 



The criteria for specific identification and separation 

 of Auxis larvae from those of other tuna and tunalike 

 fishes appear to be quite well established. Ueyanagi 

 (1964) has provided a key to identifying tuna larvae and 

 this is given below: 



Key to the larvae of tunas from 

 the western Pacific' 



a Melanophores visible on the forebrain 



bj One conspicuous melanophore present on 

 the caudal peduncle. No chromato- 

 phores on the isthmus or directly £inte- 

 rior to the anus. 



.... skipjack tuna, Katsuwonus pelamis 

 bj There is a dotted line of melanophores 

 along the midlateral line on the poste- 

 rior part of the body. Chromatophores 

 appear on the isthmus and directly an- 

 terior to the anus. 



kawakawa, Euthynnus affinis 



a No melanophores visible on the forebrain. 

 c Melanophores appear on the sides of the 

 body, 

 d Chromatophores appear on the isth- 

 mus and directly anterior to the 

 anus. Melanophores appetir as dotted 

 lines along the middorsal, midlateral, 

 and midventral lines of the caudal 

 region (usually in three lines). 

 .... frigate and bullet tunas, Auxis spp. 

 dj Chromatophores do not appear on the 



Applicable to larvae under about 8 mm TL. 



26 



