Okiyama Reproductive style of two species of sandfishes 



545 



Arctoscopus japonicus 



A , 



13.3mm 



14.2mm 



16.8mm 



17.8mm 



Trichodon trichodon 



13.0mm 





14.5mm 



-.^^ 



28.2mm 



27.0mm 



Figure 2 



Comparison between early developmental stages of Arctoscopus japomcus (left) and Trichodon trichodon (right). Size in mm SL; preserved 

 specimens (B-D after Okiyama 1988; F-J after Marliave 1981). 



(Marliave 1981). It seems that T. trichodon selected this 

 peculiar spawning location because it offered a refuge 

 from egg predation as well as the high flow velocities 

 necessary for respiration (Marliave 1981). 



These contrasting reproductive styles should be asso- 

 ciated with the different reproductive guilds proposed 

 by Balon (1981, 1984). Although A. japonicufi fits the 

 "obligatory plant spawners" category, there is no guild 

 relevant to T. trichodon within Balon's category of 

 "nonguarders," suggesting its spawning habits may be 

 unique. 



Early life history 



Larvae and juveniles of both species have been de- 

 scribed and illustrated in detail from field and/or labor- 

 atory-reared materials (Marliave 1981, Okiyama 1988). 

 In Figure 2, a series of early developmental stages of 

 these species is reproduced from these references, with 

 additional specimens of A. japonicus included. Here, 



specimens of similar sizes are selected to facilitate 

 interspecific comparison. The early growth of the two 

 species is also compared in Figure 3, based on the 

 laboratory-rearing results; the comparison reveals that 

 T. trichodon is consistently larger than A. japonicus 

 throughout the 2 months following hatching (Marliave 

 1981, Maekawa 1985). Despite close resemblances in 

 the general morphology, there are remarkable differ- 

 ences in early developmental patterns between the two 

 species. A few interesting aspects are as follows: 



(a) Newly hatched larvae of A. japonicus, 13 mm 

 notochord length (NL), are less advanced than those 

 of T. trichodon, 13.0 mm standard length (SL); the body 

 is slender, the notochord tip is straight, and fin ele- 

 ments, except several incipient caudal rays, and teeth 

 are absent. In contrast, T. trichodon possesses many 

 precocious characters, including a flexed notochord 

 with full complement of principal caudal rays, develop- 

 ing pectoral rays and preopercular spines, in addition 

 to a deeper body, larger eyes, and the presence of 



