Takao Shima

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.

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.

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.

Effects of feeding time, water temperature, feeding frequency and dietary composition on apparent nutrient digestibility in rainbow trout Oncorhynchus mykiss and common carp Cyprinus carpio

A series of experiments was conducted to evaluate the effects of feeding time (daytime vs nighttime feeding), dietary fat content (8 and 20%), feeding frequency (trout 1–3 times/day, carp 2–7 times/day), water temperature (trout 18 and 11°C, carp 25 and 17°C), on the apparent nutrient digestibility in rainbow trout and common carp. The feeding time had little effect on the macronutrient digestibility in both species. In trout, starch digestibility decreased with the decrease of water temperature and with increase of feeding frequency, but in carp, increase of the feeding frequency markedly decreased the macronutrient digestibility and phosphrrus absorption of the high fat diet. Fat digestibility of the beef tallow diet decreased relative to the pollock oil diet in carp, without affecting the phosphorus absorption. Inclusion of raw starch, the digestibility of which was lower than that of gelatinized starch, increased the phosphorus absorption in carp. These results suggest that reduction of water temperature and increase of feeding frequency notably decreased starch digestibility in trout while in carp, the effects of feeding frequency and water temperature on macronutrient digestibility and phosphorus absorption are notable for a high fat diet.

Effect of water temperature and short-term fasting on macronutrient self-selection by common carp (Cyprinus carpio)

Abstract The influence of water temperature (17 and 25 °C) and a period of fasting on the self-selection of macronutrients were examined in common carp held on a 12:12-h light/dark cycle. Eight replicate groups of juvenile carp (ca. 15 g body weight at 17 °C and 25 g at 25 °C) were fed with three test diets [high-protein (HP), high-fat (HF) and high-carbohydrate (HC) diets] by individual self-feeders for 3 weeks, followed by a 2-week period of fasting and then 3 weeks of refeeding. At 17 °C, the carp initially selected the HP and HF diets [HP/HF/HC (%)=38:40:22], whereas at 25 °C, the carp selected the HP diet over the others (55:21:24). After fasting, the carp tended to increase their demand for the HF diet at 17 °C and for the HC diet at 25 °C, but the overall self-selection of the test diets did not differ markedly from that prior to fasting. Carp held at 17 °C had higher relative whole body fat content and plasma triglyceride concentration; the latter decreased markedly during fasting. These results suggest that water temperature influences the macronutrient selection by carp: a relatively high demand for both protein and fat at 17 °C and for protein at 25 °C. Two weeks of fasting, however, did not markedly alter their macronutrient selection.

Effect of the response interval of self-feeders on the self-regulation of feed demand by rainbow trout (Oncorhynchus mykiss) fry

We studied the effect of varying response intervals of a self-feeding system on growth and feeding profiles of rainbow trout (Oncorhynchus mykiss) fry (1.53±0.55 g, mean±S.D.). Triplicate groups of 40 fish were fed a commercial trout feed for 49 days via self-feeders with response intervals adjusted to 2, 4, 15, or 60 s and a fixed reward level of 0.03 g (0.05% of initial biomass) per activation. In all groups, feeder activation occurred exclusively during the light period (07:00–19:25) with marked peaks at the artificially induced dawn and dusk. As the experiment progressed, the number of feeder activations during peak periods significantly increased in the 2 and 4 s response interval groups, but not the 15 and 60 s groups. Throughout the experiment, the amount of feed dispensed daily increased in all response interval groups. However, as the experiment progressed, the amount of feed dispensed in the 15 and 60 s groups gradually became less than the 2 and 4 s groups. There were significant negative relationships between the response interval and the feeding rate, final body weight (BWf), specific growth rate (SGR), and condition factor (CF) (P<0.05). Coefficients of variation of BWf and feed efficiency were not affected by the response interval. Results of this study indicate that the long response intervals (≥15 s) of the present self-feeder with a fixed reward level significantly restrict the ability of fish to increase the number of feeder activations to satisfy their energy requirements.