Developmental changes of swimming speed were analysed in the chub mackerel Scomber japonicus raised on two distinct dietary regimens. One group was fed only zooplankton such as rotifers and Artemia nauplii (R group) and the other group was fed rotifers plus red sea bream Pagrus major larvae (Pm group). Fish from the Pm group grew faster than those from the R group, and both the cruise and burst swimming speeds were faster for the Pm group even when match‐sized comparisons were made. Fish in the Pm group attained a standard length (SL) of 17.5 mm by day 14 and their cruise and burst swimming speeds were 5.39 SL/s and 18.45 SL/s, whereas the R group attained 17.35 mm SL by day 17 and their cruise and burst swimming speeds were 4.28 SL/s and 13.98 SL/s. The results suggest that the swimming speed of chub mackerel in the wild would develop differently depending on the food resources they happen to encounter.

SUMMARY: Diel successive samplings of Japanese Spanish mackerel Scomberomorus niphonius larvae were conducted throughout 24 h both in the sea and in captivity in order to estimate their daily ration. Using the Elliott and Persson model, the instantaneous gastric evacuation rate was estimated from the depletion of stomach contents (% dry bodyweight) with time during the night for wild fish (3.0–11.5 mm standard length) and from starvation experiments for reared fish (8, 10, and 15 days after hatching (DAH)). Japanese Spanish mackerel is a daylight feeder and exhibited piscivorous habits from first feeding both in the sea and in captivity. Feeding activity peaked at dusk. The estimated daily ration for wild larvae were 111.1 and 127.2% in 1996 and 1997, respectively; and those for reared larvae ranged from 90.6 to 111.7% of dry bodyweight. Based on the estimated value of daily rations for reared fish, the total number of newly hatched red sea bream Pagrus major larvae preyed by a Japanese Spanish mackerel from first feeding (5 DAH) to beginning of juvenile stage (20 DAH) in captivity was calculated to be 1139–1404.

The ability of newly hatched larvae of Japanese Spanish mackerel Scomberomorus niphonius to resist starvation was studied in rearing experiments. Because Japanese Spanish mackerel larvae exhibit almost complete piscivory from the first feeding stage and begin to cannibalize under lack of piscine prey, they were isolated from one another during the experiments. Newly hatched larvae commenced feeding on fish prey (red sea bream Pagrus major larvae) on day 6 (after hatching) and completed yolk sac absorption by day 9 at 18.5°C. All the starved larvae had died by day 10. More than 90% of fish fed red sea bream larvae survived until day 10, whereas all fish fed rotifer (Brachionus plicatilis) had died by the same day, indicating that rotifer is useless as a prey for the survival of Japanese Spanish mackerel larvae at the first feeding stage. A clear point‐of‐no‐return (PNR), 0–1 day of recoverable starvation, was found at the post‐first feeding stage. Delayed feeding experiments demonstrated that the percentage survival on day 10 was 100% for larvae fed from day 5, 91.6% from day 6, 16.7% from day 7, 8.3% from day 8, and 0% for those fed from day 9. Fish first fed from day 7 or 8 showed significantly retarded growth during the following adequately fed period compared with fish fed from the first feeding (day 6). These results show that Japanese Spanish mackerel larvae are highly vulnerable to fasting and that the larvae’s first feeding success might be critical for growth and survival in the period that follows.

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SUMMARY: Scombrid fish generally display a unique early development characterized by large head , fast growth, and early piscivory. Development of the digestive system, which is a crucial element for feeding and growth, was examined using laboratory-reared larvae of 5 scombrid species: Japanese Spanish mackerel Scomberomorus niphonius, striped bonito Sarda orientalis, bluefin tuna Thunnus thynnus, yellowfin tuna T. albacares, and chub mackerel Scomber japonicus.Compared with common marine fish larvae, the digestive system appeared to develop precociously in all the scombrid larvae examined, but, the timing varied with the species. Differentiation of the juvenile-type digestive system corresponded to the appearance of piscivory and acceleration of growth rate.