Effects of Feeding Newly Hatched Larvae on the Growth, Survival, and Growth Patterns of Kawakawa (<i>Euthynnus affinis</i>) Larvae and Juveniles
2025
Lynn Nuruki | Aki Miyashima | Yasuo Agawa | Yoshifumi Sawada
This study investigated the effects of feeding striped beakfish (<i>Oplegnathus fasciatus</i>) newly hatched larvae on the survival and growth of kawakawa (<i>Euthynnus affinis</i>) larvae and juveniles, as well as their relative growth patterns. Fertilized eggs of kawakawa were reared in 1 m<sup>3</sup> experimental tanks until 13 days post-hatch (dph). From 3 to 8 dph, larvae were fed enriched rotifers, and from 9 to 12 dph, they were assigned to two experimental groups: one receiving only a formulated diet and the other receiving a combination of the formulated diet and 10,000 striped beakfish newly hatched larvae every day in each tank. The group fed newly hatched larvae exhibited approximately 36% greater growth than the group fed only the formulated diet. However, survival at 13 dph was approximately 34% lower, suggesting that further investigation is needed to determine the optimal feeding quantity of newly hatched larvae. The relative growth patterns of larvae and juveniles reared in a commercial 30 m<sup>3</sup> tank showed morphological traits characteristic of scombrid fish, such as a longer preanal length and upper jaw length. Growth patterns varied at three key body lengths (notochord length or standard length; 3, 8–10, and 30 mm), as well as at their corresponding standard lengths. In kawakawa, the upper jaw exhibited early accelerated growth compared to other scombrid species. This characteristic is believed to facilitate the early onset of piscivory under captive conditions.
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