Two experiments were conducted to decide the requirement of larval striped jack Pseudocaranx dentex for eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) by feeding Artemia nauplii containing different levels of EPA and/or DHA for 11 or 12 days. Fish fed oleic acid (OA) enriched Ar temia containing a low amount of n-3 highly unsaturated fatty acids (n-3HUFA, mainly EPA and DHA) showed low growth and survival rate, and poor vitality (survival rate at activity test). Elevation of DHA levels in the nauplii improved survival, growth, and vitality. However poor vitality was ob served even though fish fed EPA enriched Artemia. Fatty acid compositions of polar lipid in fish body clearly reflected the composition of nauplii. In healthy fish with strong vitality, the ratio of 18:1/22:6n -3 in body polar lipids remained below 1. This ratio could be an appropriate index for EFA status of lar val striped jack.The requirement of larval striped jack for DHA during the Artemia feeding period is estimated to be 1.6-2.2% in Artemia (dry basis) based on larval vitality. On the other hand, fish fed EPA enriched Artemia containing more than 3.1% EPA does not improve neither vitality nor survival.

No abstract

To investigate involvement of the central nervous system in the ontogeny of behaviour, diets of differing quality were used to rear yellowtail Seriola quinqueradiata larvae and juveniles. Artemia nauplii enriched with oleic acid (OA), eicosapentaenoic acid (EPA), or two different concentration levels of docosahexaenoic acid (DHA) were fed to yellowtail larvae (L T 7 mm; 13 days old) for 12 days, and their behavioural development was analysed together with growth, survival, activity and fatty acid composition. Yellowtail fed with DHA-enriched Artemia showed mutual attraction behaviour at 11 mm L T , while those fed with OA-or EPA-enriched Artemia did not show this behaviour at the same size. While fish in the OA group showed poor growth, survival and activity index, fish in the EPA group were similar to the two DHA groups.In addition, most fish tested, including the OA group, showed clear optokinetic responses. Fatty acid composition of the diet was reflected in that of the fish body. Therefore, dietary DHA in the larval stage is considered to be essential for the development of schooling behaviour in the yellowtail. 1998 The Fisheries Society of the British Isles

Larval food abundance is one potential cause of recruitment variation in benthic invertebrates, including bivalves. Bivalve veliger larvae can clear particles <~10 µm. However, the particle retention efficiency (PRE) of bivalve larvae differs among species, so is necessary to determine larval food abundance in nature. We investigated the PRE of larvae of the asari clam Ruditapes philippinarum, which recently has greatly decreased in numbers in Japan. Artificially hatched larvae from the umbo to the full grown stage were exposed to natural food assemblages. Larval clearance rates were determined for particles in 32 size ranges from 0.8 to 18 µm. We observed significant clearance of particles in the ~1 to 8 µm size range, with the highest clearance rates being on 1.4 to 2.0 µm particles. Larval ingestion of the natural food assemblages ranged from 50 × 10 2 to 120 × 10 2 µm 3 ind., which is below the hatchery food ration, suggesting larval food limitation in nature.

No abstract