ATLANTIC SAILFISH 



169 



POSSIBLE IDENTITY OF THE DIVERGENT 

 SPECIMENS 



Speculation on the identity of the divergent 

 specimens leads through a maze of confused 

 records and contradictions. There are four gen- 

 erally recognized istiophorids in the Western 

 North Atlantic: the Atlantic sailfish, Istiophorus 

 americaini~9 (Cuvier) ; the white marlin, Malcaira 

 albida (Poey); the blue marlin, M. a/npla (Poey) ; 

 and the spearfish, Tetrapturus belone Rafinesque. 



As discussed previously, the unidentified speci- 

 mens very closely resemble young of the Atlantic 

 sailfish, but have been separated from this species 

 mainly on tlie characters of snout length and 

 snout extension. On this basis, I must place the 

 unidentified specimens in one or the other of the 

 genera Makaira or Tetrapturus. 



Adult specimens of the marlins [Makaira) are 

 separated from the spearfish {Tetrapturus) on the 

 following major characters: 



1. Length of snout and snout extension. The 

 spearfish has a much shorter snout and snout 

 extension than either the marlin or the sailfish. 



2. Shape and height of dorsal fin. The whole 

 dorsal is well developed and more uniformly high 

 in the spearfish, placing it between the marlins 

 and sailfish. 



3. Length of ventral fins. The spearfish has 

 considerably longer ventrals than the marlin, but 

 shorter than the sailfish. 



On the basis of these three characters, the 

 unidentified specimens more nearly resemble the 

 spearfish {Tetrapturus) than they do the marlins 

 {Makaira). Using the development of the sailfish 

 as a guide, it is logical to me that the unidentified 

 specimens are more likely to develop into the 

 adult form of Tetrapturus than of Makaira. 



Sparta (1953) figures and describes eggs and 

 larvae he believes to be Tetrapturus belone Rafines- 

 que. His 5.24-mm. finfold larva does not remotely 

 resemble my istiophorid specimens of a similar 

 size, and is much less developed than my 3.6-mm. 

 istiophorid. However, it rather closely resembles 

 swordfish larvae, Xiphias gladius Linnaeus, of a 

 similar size (Sanzo 1922). Sparta gave egg 

 diameters of approximately 1.48 mm. for his 

 possible T. belone Rafinesque, while Nakamura 

 (1938) reported that a hooked shortnosed spear- 

 fish, T. angustirostris Tanaka, released eggs about 

 1 mm. in diameter as it was being lifted out of 

 the water. 



SUMMARY 



1. Measurements and meristic coinits were 

 taken from 168 specimens of the family Istio- 

 phoridae, including the Atlantic sailfish Istiophorus 

 americanus (Cuvier), ranging in standard length 

 from 3.4 to 625 mm., from the waters off the 

 South Atlantic Coast of the United States and 

 the Gulf of Mexico, and selected measurements 

 were obtained from the literature on 18 specimens. 

 Twenty specimens representing the sailfish and an 

 unidentified species of istiophorid, ranging in 

 standard length from 3.6 to 374 mm., are described 

 and illustrated at sizes selected to show important 

 changes. 



2. Growth and development of various body 

 parts are discussed, summarized, and illustrated 

 with graphs, with particular reference to the sail- 

 fish. Three stages of larval development are 

 suggested: "Early larval," below 7 mm., during the 

 period of rapid development of head spines; "mid- 

 larval," the 7 to 20 mm. range, within which growth 

 of head spines ceases, the snout begins to elongate, 

 and fins receive their full complement of rays and 

 undergo changes in size and shape; and "late 

 larval," the 20 to 100 mm. range, within which 

 head spines begin to disappear, fins further 

 develop in size and shape, dermal spines develop, 

 and jaw teeth begin to disappear. 



3. Data on an unidentified species of istiophorid 

 are presented with Atlantic sailfish material, from 

 which it is distinguishable above 10 mm. in 

 standard length. Below this size, separation is 

 not made, since no valid character for separation 

 was found. Discussion of the unidentified species 

 appears where pertinent throughout the text. 

 Divergence of certain characters, in particular the 

 shorter snout and snout extension, is discussed 

 with the idea of throwing light on possible identity. 



4. Pigment is limited to a few melanophores on 

 the dorsal surface of the brain case on the 3.4-mm. 

 specimen. At 5 mm., pigment is present on sides 

 of head and body posteriorly to the anus; it 

 spreads to the caudal fin, down the sides, and 

 onto the dorsal fin at approximately 10 mm. It 

 becomes denser, extends farther down the sides, 

 and spreads generally over the anterior portion of 

 the dorsal fin at approximately 20 mm. Bars (or 

 blotches of pigment) appear on the body at approx- 

 imately 35 mm. General color of pigmentation on 

 specimens exceeding 20 mm. (except for barred 

 areas) is blue-black on the dorsal surface, grading 



