3 BIONOMICS AND LIFE HISTORY 

 3.1 Reproduction 



3.11 Sexuality 



As far as known, all billfishes, including T. 

 belone, are dioecious. Fat deposits adhering to the 

 ovaries of billfishes during their vegetative period are 

 frequently mistaken for testes by fishermen, and 

 hence it is popularly believed that some billfishes are 

 hermaphroditic. 



Sexual dimorphism is marked in the related 

 istiophorid genus Makaira (sensu stricto), with the 

 females growing to a much larger size (de Sylva, 

 1963a). Nakamura (1949) noted that the Pacific T. 

 angustirostris did not exhibit sexual dimorphism, 

 there being no difference in the mean weight of males 

 and females. 



Robins and de Sylva (1963:96) found that their data 

 on the mean weight of males and females of T. belone 

 were inadequate. No difference in mean size of the 

 sexes was found in the related T. albidus, according to 

 de Sylva and Davis (1963). There is no evidence that 

 there are sexual differences in color or morphometric 

 characteristics in T. belone. 



3.12 Maturity 



Nothing is known regarding the size or weight at 

 which sexual maturity is reached in T. belone. 



3.13 Mating 



The spawning act has not been observed, nor is 

 anything known about the location of spawning. 

 Rafinesque (1810) commented that the fish usually 

 travel in pairs, a male and a female together, and that 

 very often both are captured together. 



3.14 Fertilization 



Reproductive behavior or fecundity have not been 

 studied. Undoubtedly, fertilization is external. Sparta 

 (1953, 1961) has described the pelagic eggs, from the 

 plankton, of T. belone. 



3.15 Gonads 



Robins and de Sylva (1963:96) noted that the sex of 

 27 specimens of T. belone was difficult to determine. 

 This may be because they were examined in August, 

 which should represent a refractory period when the 

 gonads are not well developed, if the hypothesis of 

 Sparta (1953) is correct that spawning occurs from 

 spring to summer. That Sparta (1961) found eggs in 

 the plankton in May would further suggest that 

 spawning is long complete by August. 



The gonads of 27 fish examined from Sicily were 

 asymmetrical, "X -shaped (the left side longer in one 



female, the right side longer in most others), and very 

 orange (Robins and de Sylva, 1963:96). 



3.16 Spawning 



Sparta (1953) reported on eggs and larvae from the 

 Strait of Messina. He identified eggs from plankton 

 taken in May. The identity of the larvae, 4.88 and 5.24 

 mm, is questionable (Gehringer, 1956:169; Ueyanagi, 

 1962:186; Robins and de Sylva, 1963:95). Subsequent- 

 ly, Sparta (1961) indicated the spawning period as 

 spring to summer. The difficulty encountered in iden- 

 tifying the sex of gonads from 27 specimens of T. 

 belone collected in August from Sicily suggests that 

 spawning did not occur during this period. The oc- 

 currence of juveniles in October (Sparta, 1961:20) also 

 suggests a late-spring spawning period. However, an 

 earlier spawning season (i.e., winter months) cannot 

 be precluded. A spawning season of December 

 through February is postulated for T. pfluegeri in the 

 western Atlantic by de Sylva and Breder, 4 and a 

 winter or spring spawning season might not be an un- 

 reasonable hypothesis for T. belone. Ueyanagi, 

 1962:188; Ueyanagi (in Howard and Ueyanagi, 

 1965:103) concluded that T. angustirostris spawned 

 more intensively in winter in the Pacific. 



Spawning has not been observed, but larval stages 

 of T. pfluegeri have been reported from far offshore 

 (de Sylva and Ueyanagi (see footnote 3)). Other 

 istiophorids (excluding the neritic Istiophorus) appear 

 to spawn far from shoal water, and it is likely that T. 

 belone similarly spawns offshore. 



3.2 Pre-Adult Phase 



3.21 Embryonic phase 



The pelagic eggs of T. belone collected from the 

 plankton are described in detail by Sparta (1953, 

 1961). The eggs averaged 1.48 mm in diameter and the 

 oil globule was yellow-green. The eggs were incubated 

 for several days and their development is described in 

 detail. 



3.22 Larval phase 



Two larval specimens of T. belone collected near 

 Capri, off Punta Campanella, were described by Lo 

 Bianco (1903:127, 166, 238). Comparisons of these 

 specimens with other istiophorid larvae were made by 

 Lo Bianco (1909:755). Larvae from Messina reported 

 by Sparta (1953) do not seem to be those of 

 istiophorids (Gehringer, 1956:169; Ueyanagi, 

 1962:186; Robins and de Sylva, 1963:95-96). Larger 

 specimens (29 and 54 mm) were reported from the 

 coast of Faro, Strait of Messina, apparently thrown 

 ashore from the southeast wind (Sirocco). These two 



*de Sylva, D. P., and P. R. Breder. Gonad histology and repro- 

 ductive cycle in the Atlantic species of the Istiophoridae. Manu- 

 script in preparation. Rosenstiel School of Marine and Atmo- 

 spheric Science, University of Miami, Miami, FL 33149. 



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