MATSUMOTO ET AL.: LARVAL TUNA IDENTIFICATION 



Table 4. — Characters used to separate larvae of Thunnus species having black pigmentation on trunk. 



Characters 



Thunnus thynnus 

 (Atlantic) 



Thunnus thynnus 

 (Pacific) 



Thunnus tonggot 



Thunnus maccoyii 



Thunnus ohesus 



Small larvae (3-10 mm SL): 



Number of black pigment 

 cells: 



Upper jaw tip 



Lower jaw tip 



Dorsal edge trunk 



Lateral lino 



Ventral edge trunk 



Number of red pigment 

 cells: 



Dorsal edge trunk 



Lateral line 

 Ventral edge trunk 



Lower jaw ventral 

 view 



Large larvae (>10 mm SL): 



Array of ^D^ pterygio- 

 phores between two 

 adjacent neural spines 



No observation 



2 on inner edge 



1 or 2 



0-2 near mid-trunk 



M 



Streak on caudal 

 peduncle'^ 



Indistinct! 



Streak anus to caudal 

 peduncle^ 



Streak along margin 

 anterior half of jaw 

 and midline^ 



1, 2, 2, 3, 2, 2, 1, 1 



Appears above 6 mm 

 SL 



2 on inner edge 

 above 4 mm SL 



1 or 2 

 None 



2 or more 



1-5, mostly 3 



Number not available 

 Number not available 



2 well spaced on 

 anterior half 



No observation 



No observation 



No observation 



1, 2, or more 



None 



2 or more 



No observation 



No observation 

 No observation 



No observation 

 No observation 



Appears above 5 mm Few spots above 5 mm 



SL SL 



Appears above 4 mm 0-2 on inner edge 



SL below 4 mm SL 



1 or 2, very small None 



or 1 near mid-trunk None 



1-3 1 or more 



No observation 



No observation 

 No observation 



No observation 



No observation 



0, 1, (2) 



0, 1, 2, 3, 4 



1-8 [mean = 5.3] 



1 on each side near tip 



1, 2, 2, 2, 3, 2, 1, 1 



• Only one larva taken in a day tow was examined. 

 2 D2 refers to second dorsal fin. 



ment cells were present along the base of the 

 posterior half of the anal fin. Red pigmentation 

 did not differ from that in T. albacares. 



In larger larvae (10-13 mm SL) the array of 

 pterygiophores of the second dorsal fin between 

 two adjacent neural spines was sufficient to sep- 

 arate T. thynnus from T. ohesus and both species 

 from T. alalunga (Tables 2 and 3). In T. thyn- 

 nus the greatest number of pterygiophores (3) 

 between two adjacent neural spines appeared in 

 the fourth position in the array, whereas in T. 

 ohesus and T. alalunga it appeared in the fifth 

 and sixth positions, respectively. T. ohesus was 

 not distinguishable from T. alhacares by this 

 character. 



The identification of T. atlanticus was not re- 

 solved. No larvae from the distributional range 

 of this species (tropical western Atlantic) have 

 been found which are distinguishable from any 

 of the species considered above. One of us 

 (Richards) suspects that T. atlanticus larvae 

 are very similar to larvae of T. ohesus. This 

 suspicion is based on the great abundance of 

 larvae resembling those of T. ohesus in this area, 

 particularly at times and places where T. ohesus 



adults are rarely found or absent, 

 studies are needed. 



Further 



SUMMARY OF LARVAL IDENTIFICATION 



On the basis of the examination and discussion 

 above, the workshop agreed that: 



1. The description of T. albacares by Matsu- 

 moto (1958) was correct (see Figures 1 and 2), 

 but that the "appearance of black pigmentation 

 at the tip of the lower jaw at about 4.5 mm SL" 

 should be included. 



2. The description of T. alalunga by Yabe and 

 Ueyanagi (1962) and illustrations by Ueyanagi 

 (1969) were correct (see Figures 3 and 4), but 

 that the lower size limit should be set at about 

 4.5 mm SL until further studies indicate more 

 precisely the earlier appearance of black pig- 

 mentation at the tip of the lower jaw in T. al- 

 hacares. 



3. It is not possible to separate larvae of T. 

 alhacares from T. alalunga below 4.5 mm SL, 

 prior to the appearance of black pigment cells 

 at the tip of the lower jaw in T. alhacares. 



4. The description of T. thynnus by Yabe, 

 Ueyanagi, and Watanabe (1966) was correct 



