371 



Abstract— Distribution of eggs and 

 larvae and feeding and growth of 

 larvae of Japanese Spanish mack- 

 erel iScomberomorus niphonius) were 

 investigated in relation to their prey 

 in the Sea of Hiuchi, the Seto Inland 

 Sea. Japan, in 1995 and 1996. The 

 abundance of S. niphonius eggs and 

 larvae peaked in late May, corre- 

 sponding with that of clupeid larvae, 

 the major prey organisms of S. nipho- 

 nius larvae. The eggs were abundant 

 in the northwestern waters and the 

 larvae were abundant in the south- 

 ern waters in late May in both years, 

 indicating a southward drift during 

 egg and yolksac stages by residual 

 flow in the central part of the Sea of 

 Hiuchi. Abundance of clupeid larvae 

 in southern waters, where S. nipho- 

 nius larvae were abundant, may indi- 

 cate a spawning strategy on the part 

 of first-feeding S. niphonius larvae 

 to encounter the spatial and tem- 

 poral peak in ichthyoplankton prey 

 abundance in the Seto Inland Sea. 

 Abundance of the clupeid larvae was 

 higher in 1995 than in 1996. Feed- 

 ing incidence (percentage of stomachs 

 with food; 85.3% in 1995 and 67.7% 

 in 19961 and mean growth rate esti- 

 mated from otolith daily increments 

 (1.05 mm/d in 1995 and 0.85 mm/d 

 in 1996) of S. niphonius larvae in 

 late May were significantly higher 

 in 1995. Young-of-the-year S. nipho- 

 nius abundance and catch per unit of 

 fishing effort of 1-year-old S. nipho- 

 nius in the Sea of Hiuchi was higher 

 in 1995, indicating a more successful 

 recruitment in this year. Spatial and 

 temporal correspondence with high 

 ichthyoplankton prey concentration 

 was considered one of the important 

 determinants for the feeding success, 

 growth, and survival of S. niphonius 

 larvae. 



Distribution, feeding condition, 

 and growth of Japanese Spanish mackerel 

 iScomberomorus niphonius) larvae 

 in the Seto Inland Sea 



Jun Shoji 



Masaru Tanaka 



Laboratory of Estuanne Ecology 



Field Science Education and Research Center 



Kyoto University 



Kita-shirakawa, Sakyo, Kyoto 606-8502, Japan 



E-mail address (for J Sho|i): shogG'kais.kyoto-uaC-ip 



Manuscript submitted 12 February 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



28 December 2004 by the Scientific Editor. 



Fish. Bull. 103:371-379 12005). 



Scombrid fishes are considered to have 

 adopted a survival strategy charac- 

 terized by fast growth and the abil- 

 ity to consume large prey at an early 

 age (Hunter, 1981). Their larvae have 

 morphological features such as large 

 eyes and mouths, with which piscivory 

 and fast growth can be achieved in 

 early life stages. Among scombrids, 

 extremely early piscivory and fast 

 growth have been observed in the 

 early life stages of Spanish mackerels 

 iScomberomorus fishes). Fish larvae 

 were dominant in stomachs of Scomb- 

 eromorus larvae in three regions: 1) S. 

 semifasciatus, S. queenslandicus, and 

 S. commerson, in Australian waters 

 (Jenkins et al., 1984), 2) Spanish 

 mackerel (S. maculatus) and king 

 mackerel (S. cavalla) in the south- 

 eastern United States (Finucane et 

 al., 1990), and 3) Japanese Spanish 

 mackerel (S. niphonius) in the Seto 

 Inland Sea, Japan (Shoji et al., 1997). 

 Larval growth rate was reported to 

 be approximately 1.0 mm/d in king 

 and Spanish mackerels (DeVries et 

 al., 1990; Peters and Schmidt, 1997) 

 and S. niphonius (Shoji et al., 2001). 

 Tanaka et al. (1996) demonstrated 

 precocious development of an adult- 

 type digestive system (with a func- 

 tional stomach and pyloric caecum) 

 occurred in first feeding S. niphonius 

 larvae. They suggested that Scomb- 

 eromorus fish have adopted a special- 

 ized feeding strategy, namely piscivory 

 and fast growth from the time of first 



feeding, which reduces the duration of 

 the larval stage, the period of great- 

 est vulnerability to predation ( Houde, 

 1987). 



Ichthyoplankton prey seem to be 

 indispensable for growth and survival 

 during larval period of Scorn beromorus 

 fish. Under laboratory conditions, Fu- 

 kunaga et al. (1982) reported that S. 

 niphonius larvae preferred fish larvae 

 to invertebrate plankton prey (roti- 

 fer and Artemia nauplii). Shoji and 

 Tanaka (2001) demonstrated that S. 

 niphonius larvae began to cannibal- 

 ize siblings when they were supplied 

 with only invertebrate plankton prey. 

 Scomberomorus larvae would need to 

 exert greater searching effort and to 

 swim fast to capture ichthyoplank- 

 ton prey because they are larger and 

 much less abundant in water than 

 invertebrate plankton prey (Sheldon 

 et al., 1972). Scomberomorus larvae 

 with a high swimming performance 

 have been shown to have high levels 

 of larval mortality due to starvation. 

 Margulies (1993) demonstrated by 

 histological analysis that Pacific sier- 

 ra (S. sierra) larvae could not survive 

 beyond 48 hours without feeding in 

 the Panama Bight. Shoji et al. (2002) 

 observed that the point-of-no-return 

 for S. niphonius larvae was one day 

 after first feeding in laboratory ex- 

 periments. Scomberomorus niphonius 

 larvae fed after 1- or 2-days starva- 

 tion showed significantly retarded 

 growth during the following period 



