Toshihisa Arakawa

The effect of bacterial additives on the production rate and dietary value of rotifers as food for Japanese flounder, Paralichthys olivaceus

Two food additives containing live lactic bacteria were given to S-type rotifers fed on live algae and bakers yeast. One of them improved the production rate of rotifers (59 rotifers ml−1 day−1) in comparison with the control group fed without any additive (48 rotifers ml−1 day−1). The second additive did not improve the production rate (42 rotifers ml−1 day−1), but it improved the dietary value of the rotifers. Indeed, at day 18, the mean length of Japanese flounder fed on these rotifers (7.5 mm) was significantly higher than that of the control group (7.3 mm). The total amount of aerobic bacteria in rotifers was also affected by this additive. Three thousand bacteria per rotifer were recorded in the production tanks. Bacterial growth was particularly high during the enrichment phase. After 17 h of enrichment with an emulsion of cuttlefish liver oil, 99 000 bacteria were counted per control rotifer. The second bacterial additive limited the bacteria to 54 000 per rotifer after 17 h of enrichment. This may be a reason why this additive improved the dietary value of the rotifers.

マダイの産卵に対するイカミ-ルおよびオキアミ中の有効成分〔英文〕

Red seabream broodstock were fed various diets of different nutritional quality for either 26 days or shortly before spawning to clarify the effective components in cuttlefish meal and raw krill which aid in quality egg production. The percentage of buoyant eggs was lowest in the control group receiving the white fish meal diet, and was elevated by the addition of 200mg DL-ƒ¿-tocopheryl acetate. The value was also effectively improved by replacement of white fish meal with defatted or intact cuttlefish meal as a protein source. Feeding broodstock with frozen raw krill after previously being fed control diet resulted in elevation of the percentage of buoyant eggs and normal larvae. Equally good results were obtained by substitution of cuttlefish liver oil in the control diet with 2.5% krill polar lipid or 2.5% krill nonpolar lipid. However, neither defatted krill meal nor fat-soluble fraction of cuttlefish meal showed the good effect on the egg quality. Consequently, the superior quality of cuttlefish meal to the white fish meal as a protein source for red seabream broodstock diets was reconfirmed. And the effective components in raw krill, aiding the reproduction of red seabream, are suggested to be the polar and nonpolar lipid fractions. In addition, vitamin E was also found to have the same efficiency for improvement of the egg quality.

Evaluation of larval quality of viviparous scorpionfish Sebastiscus marmoratus

The aim of this study was to develop an acute test for larval quality in the viviparous scorpionfish Sebastiscus marmoratus. Rearing experiments until day 13 post parturition were conducted to investigate the survival of larvae for 13 different batches, and tolerance to starvation of larvae was examined and expressed by the survival activity index (SAI). The morphological characters, enzyme activity, and swimming behavior of larvae on day 0 and 1 were also observed, followed by the correlation analysis between SAI. Larvae with high SAI (≥26) showed significantly higher survival on day 13 than larvae with low SAI, which confirmed that SAI is a reliable index that can be used to evaluate larval quality, similar to the former findings. The esterase activity (r=−0.713, P<0.01), swim frequency (r=−0.735, P<0.01) and swimming speed (r=−0.588, P<0.05) of larvae on day 0 were significantly and negatively correlated with SAI. It was concluded that enzyme activity and behavioral characters of larvae just after parturition can be a real-time index for evaluating the larval quality of this species.