Hirofumi Furuita

Effect of arachidonic acid levels in broodstock diet on larval and egg quality of Japanese flounder Paralichthys olivaceus.

This study investigated the effect of dietary arachidonic acid (AA) in broodstock of Japanese flounder on subsequent egg and larval quality. Diets with similar proximate composition and n-3 HUFA level, but with different AA levels (0.1%, 0.6% and 1.2% of diet), were fed to the broodstock from 3 months before and during the spawning season. Spawning was observed from March to May. Total egg production over the spawning season was highest in fish fed the 0.6% AA diet and lowest in fish fed the 1.2% AA diet. All parameters measured as egg quality (percentage of buoyant eggs, hatching rate, larval survival and normality of larvae.) were highest in fish fed the 0.6% AA diet. AA content in eggs proportionally increased with the dietary AA level. EPA content of polar lipids of eggs had a negative correlation with the AA level in diets whereas the DHA content was independent of dietary AA. The results of this study indicate that a supplement of AA at 0.6 g/100 g diet improved the reproductive performance of Japanese flounder, but a higher level of AA (1.2 g/100 g diet) negatively affected both egg and larval quality due to a potential inhibitory effect on EPA bioconversion.

Effects of n-3 HUFA levels in broodstock diet on the reproductive performance and egg and larval quality of the Japanese flounder, Paralichthys olivaceus

Abstract We investigated the effect of dietary n−3 highly unsaturated fatty acids (n−3 HUFA) on egg and larval quality in the Japanese flounder Paralichthys olivaceus. Diets with similar proximate composition, but different n−3 HUFA (0.4%, 0.8%, and 2.1%) levels were fed to broodstock from 3 months before and during the spawning season. Spawning was observed from March to June. Total egg production was highest in fish fed the lowest n−3 HUFA, and decreased with the increase of dietary n−3 HUFA. Percentages of buoyant eggs and hatched larvae were independent of dietary treatment. In contrast, the percentage of normal larvae, survival of larvae at 3 days post hatching (DPH), and the starvation tolerance index correlated with dietary n−3 HUFA levels. n−3 HUFA level in eggs increased with the increase of dietary level. Higher level of arachidonic acid (AA) was also found in eggs that showed high quality, reflecting dietary fatty acids. The results of this study clearly show that n−3 HUFA level in broodstock diet has an effect on the quality of eggs and larvae in the Japanese flounder and suggested that AA may have positive effect on the improvement in spawning quality of flounder.

Effects of high levels of n-3 HUFA in broodstock diet on egg quality and egg fatty acid composition of Japanese flounder, Paralichthys olivaceus

Abstract We investigated the effect of high levels of n−3 highly unsaturated fatty acids (n−3 HUFA) in broodstock diet on egg quality and chemical composition of eggs of Japanese flounder. The broodstock were fed diets containing three levels of n−3 HUFA (2.1%, 4.8% or 6.2%) 2 months before and during the spawning period. No significant difference was found for weight gain of broodstock among the treatments. Egg production was highest in fish fed the highest level of n−3 HUFA. However, egg quality parameters, such as percentage of buoyant eggs, hatching rate and percentage of normal larvae, were significantly higher in the group fed the lowest n−3 HUFA diet. The fatty acid composition of eggs was influenced more markedly in the neutral lipid fraction than in the polar lipid fraction by dietary n−3 HUFA levels. Arachidonic acid (AA; 20:4n−6) and egg quality parameters both decreased with increasing dietary n−3 HUFA levels. The results suggest that a high level of n−3 HUFA in broodstock diet negatively affects egg quality of Japanese flounder.

Effect of different levels of eicosapentaenoic acid and docosahexaenoic acid in Artemia nauplii on growth, survival and salinity tolerance of larvae of the Japanese flounder, Paralichthys olivaceus

Abstract Variations in growth, survival and salinity tolerance of Japanese flounder larvae were studied after feeding Artemia nauplii enriched with different levels of unsaturated fatty acids. Fifteen-day-old larvae were fed nauplii enriched with various levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for 25 days. Growth of larvae was significantly improved by feeding Artemia containing increased levels of n-3 HUFA, but there was no clear difference between the effect of EPA and DHA on growth. In contrast, those fed Artemia enriched in oleic acid showed poor growth and had low survival. Survival of larvae after high salinity water (65‰) treatment (salinity tolerance test) was significantly improved by an increase of DHA content in Artemia, but not by EPA. These results indicate that DHA is superior to EPA as an essential fatty acid (EFA) from view point of the salinity tolerance of the larvae. The DHA requirement of Japanese flounder larvae is suggested to be about 1.6% in the presence of 1.0% EPA dry weight of Artemia nauplii (3.0% total n-3 HUFA).

Effects of eicosapentaenoic and docosahexaenoic acids on growth, survival and brain development of larval Japanese flounder (Paralichthys olivaceus)

An investigation is reported on the effects of arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on the growth and survival of larval Japanese flounder (Paralichthys olivaceus). The effects of dietary EPA and DHA on brain development in larvae were also investigated. Fifteen-day-old larvae were fed Artemia nauplii enriched with these fatty acids for 25 days. Larvae fed with Artemia enriched with oleic acid had low survival and poor growth. The survival and growth of larvae were improved by the addition of AA, EPA or DHA to their diet. However, AA was inferior to EPA and to DHA as an essential fatty acid (EFA). The relative volume of the cerebellum (volume of the cerebellum/total volume of the brain) of larvae fed EFA-deficient Artemia was significantly lower than that of larvae fed nauplii enriched with EPA or DHA. Other parts of the brain such as the telencephalon and the diencephalon revealed no significant difference among treatments. Thus, not only survival and growth, but also development of the brain, and of the cerebellum in particular, in larval Japanese flounder, was influenced by dietary EPA and DHA.

Supplemental effect of bile salts to soybean meal-based diet on growth and feed utilization of rainbow trout Oncorhynchus mykiss

A feeding experiment was conducted to evaluate the supplemental effect of bile salts to a defatted soybean meal-based non-fish meal diet for rainbow trout Oncorhynchus mykiss. A fish meal-based diet (FM) and two non-fish meal diets with and without bovine bile salts (SC+B and SC, respectively) were fed to fish (13 g initial weight) for 10 weeks. Fish fed diet SC showed inferior growth and feed efficiency, while bile salt supplementation improved the parameters to the same levels as fish fed diet FM. Crude fat and starch digestibility of diet SC-fed fish decreased after the 10-week feeding trial compared to the data obtained with fish that had no experience of the diet. Total biliary bile salt content and intestinal maltase activity of fish fed diet SC were the lowest among treatments, while these parameters were improved by bile salt supplementation. Morphological changes occurred in the distal intestine and liver of the diet SC group, although the histological features of fish fed diet SC+B were similar to those of fish fed diet FM. These results suggest that bile salt supplementation to a soybean meal-based diet improves the nutrient utilization by normalizing digestive processes in rainbow trout.

Influence of feeding diets with and without fish meal by hand and by self-feeders on feed intake, growth and nutrient utilization of juvenile rainbow trout (Oncorhynchus mykiss)

Feed intake, growth performance and nutrient utilization by juvenile rainbow trout fed diets with and without fish meal were compared between two feeding regimes: manual feeding and self-feeding. A fish meal-based diet and two non-fish meal diets, fortified with and without essential amino acids (EAA) to simulate the EAA composition of the fish meal diet, were prepared. The two non-fish meal diets were composed mainly of extruded defatted soybean meal (ExSBM), meat and bone meal (MBM) and corn gluten meal (CGM). Each diet was fed to four replicate groups (initial BW; 19.0±2.3 g, 700 g/60 l tank) either by hand to apparent satiation twice daily (0800 and 1730 h) or by self-feeders (feeds were dispensed by fish demands during the light phase) for 60 days at 17 °C under a 14 h light and 10 h dark cycle. Feeding regime did not significantly affect feed intake, weight gain, protein and energy retention, or whole body proximate composition (P>0.05). Fish fed with the non-fish meal diet with EAA supplementation attained equivalent weight gain and retention of protein as the fish fed with the fish meal diet. However, these parameters for fish fed with the non-fish meal diet without EAA supplementation were significantly inferior (P<0.05). The whole body fat content of fish fed with this diet was significantly higher than that of fish fed with the other diets. Free EAA levels in the plasma of fish fed with the EAA supplemented non-fish meal diet were similar to those fed with the fish meal diet except for threonine, which was lower in the EAA supplemented non-fish meal diet group. The branched-chain amino acid levels in the plasma of the two non-fish meal diet groups fed by hand increased more sharply and reached higher levels after feeding compared with fish fed with the same diets by self-feeders. The low levels of free threonine, methionine and lysine in the dorsal white muscle of fish fed with the EAA-unsupplemented non-fish meal diet increased in fish fed with the EAA supplemented non-fish meal diet, this increase was especially notable in the manually fed fish. Free non-essential amino acid levels in muscle of fish fed with the non-fish meal diet without EAA were generally the highest among the treatments. The feeding regime affected the levels of serine, glycine and hydroxyproline levels in the muscle (manual feeding<self-feeding). The results of this study indicate that a combination of ExSBM, MBM and CGM, when EAA are supplemented, has the potential to totally replace fish meal in juvenile rainbow trout diets. Feeding diets by self-feeders proved to attain growth and feed performance comparable to those fed by hand. Self-feeding non-fish meal diets affected certain amino acid levels in the plasma and muscle but the effects were not reflected in their growth and protein utilization in this 60-day feeding period.

Effect of taurine supplemented practical diet on growth performance and taurine contents in whole body and tissues of juvenile Japanese flounder Paralichthys olivaceus

The effect of dietary taurine on juvenile Japanese flounder was determined by feeding three taurine-supplemented experimental diets (TAU) and a commercial diet (CD) to evaluate a practical diet for juvenile Japanese flounder. Juvenile Japanese flounder were reared on the three experimental diets supplemented with taurine at 0, 0.5, 1.0% and CD. These diets were fed to juvenile Japanese flounder of an initial mean body weight of 0.2 g for 6 weeks at 20°C and the taurine contents of the whole body and tissues were analyzed. The final average body weight of juvenile Japanese flounder fed the 1.0% TAU was significantly higher than that of the other groups. Taurine contents in the whole body and tissues increased with the increase in dietary taurine level. These results indicate that juvenile Japanese flounder require at least 15 mg/g taurine in the diet, even though a combined mix of fish, krill and squid meal was the main protein source in the experimental diets.

Antagonistic effects of branched-chain amino acids induced by excess protein-bound leucine in diets for rainbow trout (Oncorhynchus mykiss)

Three feeding experiments were conducted to evaluate the antagonistic effects induced by excess leucine (Leu), derived from intact protein (zein or corn gluten meal (CGM)), on growth and protein utilization of fingerling rainbow trout (Oncorhynchus mykiss). In Experiment 1, three semipurified diets containing wheat gluten+limiting essential amino acids (EAA), zein+EAA, or zein+EAA+isoleucine (Ile)+valine (Val), were fed for 6 weeks by self-feeders. In Experiment 2, the three diets used in Experiment 1 and a zein diet with EAA and levels of Ile and Val enrichment at one half the amounts used in Experiment 1 were fed by hand for 6 weeks. In Experiment 3, a fish meal diet and three non-fish meal diets containing 23.5% CGM supplemented either with non-essential amino acids, EAA, or EAA+Ile+Val, were fed by hand for 60 days. In Experiment 1, growth and N retention of fish fed the zein diets, regardless of the Ile and Val enrichment, were inferior (P 0.05) from those of fish fed the wheat gluten diet. In Experiment 3, fish fed the two non-fish meal diets with EAA supplementation, regardless of the Ile and Val enrichment, showed identical growth and protein utilization to those of fish fed the fish meal diet. Free Ile and Val concentrations in the plasma, liver and muscle of fish fed the zein and CGM diet without Ile and Val enrichment were lower than those of fish fed the wheat gluten diet and fish meal diet, respectively, whereas the Ile and Val enrichment restored the concentrations. These results suggest that antagonisms induced by excess Leu from zein occur in rainbow trout. A practical level of CGM inclusion had no adverse effect on growth performance in a 60-day feeding, however, certain antagonisms appear in tissue branched-chain amino acid (BCAA) concentrations.

Self-selection of diets with different amino acid profiles by rainbow trout (Oncorhynchus mykiss)

Abstract The ability of rainbow trout to self-select a suitable feed among semi-purified diets with (1) a high protein (crude protein; CP=40%) and a balanced amino acid profile (casein:gelatin=6:1, BAL), (2) a high protein and an imbalanced amino acid profile (1:6, IMB), (3) a low protein (CP=15%) and a balanced amino acid profile (LP), and (4) a protein-free diet (PF), were examined using self-feeders. In experiment 1, combinations of two diets (BAL and IMB; BAL and PF; IMB and PF) were used. For each combination, four individually housed trout were provided with the diets. After an initial 2-week period, the positions of the two feed containers were exchanged and feeding continued for 3 more weeks. In the first 2 weeks, trout predominantly selected the BAL diet to the IMB or PF diet, although some fish failed to switch when the feeders were exchanged to obtain the BAL diet during the latter 3 weeks. In experiment 2, two combinations of four diets, BAL, two IMB and PF, or LP, IMB and two PF, were each offered to five individual trout for 3 weeks. Trout then showed preference for the BAL diet to the IMB and PF diets, and the LP diet to the IMB and PF diets. The preference for the BAL or LP diet gradually increased as the feeding trial progressed. These results suggest that trout preferred a casein-rich balanced amino acid diet regardless of its dietary protein level to a gelatin-rich imbalanced diet or a protein-free diet.