Milton et al.: Reproductive biology and egg production of three species of Clupeidae 



I 13 



proximate stimuli for spawning 

 of A. sirm in Kiribati. Tempera- 

 ture was constant throughout 

 the year and rainfall was 

 higher at all sites in Kiribati 

 between December and April, 

 when spawning activity was 

 lowest. Most spawning activity 

 in this species occurred during 

 the second half of the year 

 when the prevailing wind di- 

 rection changed from east to 

 west, associated with the north- 

 west monsoon that starts at 

 this time (Burgess, 1987 5 ). Our 

 limited wind and rainfall data 

 did not indicate that increased 

 spawning activity in A. sirm 

 was related to the shift in 

 weather pattern. 



Gonad maturation and 

 spawning were also linked to 

 changes in fish liver-weight 

 (HSI), visceral fat, and condi- 

 tion of each species. Either HSI 

 or fat index and condition were 

 all significantly reduced in 

 postspawning fish. Amblygas- 

 ter sirm stores energy in the 

 viscera rather than in the liver. 

 Other multiple-spawning clup- 

 eoids also transfer energy from 

 stored fat to reproductive tis- 

 sue (Dahlberg, 1969; Okera, 

 1974; Hunter and Leong, 1981). 

 In contrast, spent H. quadrimaculatus and S. 

 delieatulus had reduced HSI, which suggests that 

 the liver is the energy store utilized during repro- 

 duction (Diana and MacKay, 1979; Smith et al., 

 1990). Energy stored in this organ would be readily 

 available for rapid assimilation; hence, fish could 

 spawn multiple batches of eggs rapidly. 



Studies of temperate herring, Clupea harengus, 

 have shown that gonad maturation is linked to food 

 availability and fat storage (Linko et al., 1985; 

 Henderson and Almatar, 1989; Rajasilta, 1992). 

 Ovaries of all three species in Kiribati and of S. 

 delieatulus in the Solomon Islands (Milton and 

 Blaber, 1991) vary in a similar way to herring. 

 Milton and Blaber (1991) did not find a direct rela- 

 tion between spawning and prey availability. This 

 suggests that while gonad maturation in these clu- 



5 Burgess, S. M. 1987. The climate of western Kiribati. New 

 Zealand Meterological Service, Wellington, NZ. Miscellaneous 

 publ. 188, part 7. 



