Kenji Takii’s research while affiliated with Kindai University and other places

Simple Summary The high price and decreasing supply of fish meal (FM) has prompted the search for alternatives to achieve true sustainability in the aquaculture industry. This series of studies evaluated the complete replacement of FM by fish residue meal (FRM) in the diet of red sea bream, Pagrus major. The results revealed that FM can be completely replaced by FRM without compromising growth performance and health status. Abstract Three experiments were performed to explore (i) the complete replacement of fish meal (FM) with a combination of fish residue meal (FRM, 65% round discarded fish + 35% byproduct), soy protein concentrate (SPC) from soymilk and corn gluten meal (CGM) in Trial 1 and (ii) the utilization of diets composed of increasing byproducts in FRM in the summer (Trial 2) and winter (Trial 3) seasons. In Trial 1, the ratio of (SPC + CGM):FM in the control diet (C) was 8:2. The FM component from diet C was replaced with FRM (diet, RM20), where the ratio of (SPC + CGM):FRM became 8:2, and this ratio was changed to 6:4, 4:6 and 2:8, and referred to as RM40, RM60 and RM80, respectively. In Trials 2 and 3, the ratios of round discarded fish and byproducts in FRM were adjusted to 65:35 (FRM1), 30:70 (FRM2) and 0:100 (FRM3), and the FRM component from diet RM40 in Trial 1 was replaced with FRM1, FRM2 and FRM3 to formulate diets RM1, RM2 and RM3, respectively. In Trials 1, 2 and 3, rearing periods were 10, 8 and 12 weeks, respectively. In Trials 1 and 3, there were no significant differences in growth parameters, nutrient retention efficiency or plasma constituents among the treatments, irrespective of the inclusion levels of FRM in the diets (p > 0.05). Although there were no significant differences in final mean weight (p > 0.05), daily feeding rate and feed conversion ratio in diet RM3 were significantly higher and lower, respectively, compared to the control group in Trial 2 (p < 0.05). These results suggest that FM can be entirely replaced with FRM, and that the total elimination of round discarded fish from FRM does not affect growth or health status in red sea bream either in summer or winter seasons.

Changes in nutritional constituents and enzyme activities were clarified in yellowfin tuna (YFT, Thunnus albacares) eggs during embryonic development, from eggs immediately after fertilization to hatching. The protein levels in the eggs gradually increased with development until the completion of hatching. In contrast, the triglyceride (TG) and free amino acid (FAA) levels in the eggs gradually declined with embryonic development until hatching was complete, although the energy composition of the FAAs was lower than that of the TGs throughout embryonic development. These results indicate that endogenous TGs are preferentially expended as an energy source during embryonic development. Overall, changes in the activities of aspartate aminotransferase, alanine aminotransferase, creatine kinase, and alkaline phosphatase showed similar patterns throughout development. First, the enzyme levels diminished; then, they remained at constant, low levels just before hatching, when they rapidly increased. This rapid increase was consistent with the protein content, suggesting that organ differentiation and functionalization were promoted during this period. These results will contribute to the establishment of mass-seeding production of YFT.

A rearing study was undertaken to investigate whether trypsin inhibitor (TI) activity reduction in soy protein concentrate (SPC) derived from soymilk can afford more replacement of fish meal (FM) protein in the diet of juvenile red sea bream, Pagrus major. A diet containing 67% FM as the sole protein source was used as the control (C). SPC products with TI activities of 36, 21 and 13 TIU/mg sample were prepared. Approximately 80% of FM protein in diet C was replaced by a combination of SPC products and corn gluten meal (4:1) and referred to as T36, T21 and T13, respectively. Aqueous krill extract (KE) was added at 1% in diets T36, T21 and T13 and termed T36K, T21K and T13K, respectively. Phytase was supplemented at 1000 FTU/kg diet in all SPC-based diets. Each of seven diets was fed to a group of 20 fish (mean weight 19 g) in triplicate twice per day to apparent satiation for 10 weeks. The final mean weight (P = 0.001), specific growth rate (SGR) (P = 0.001) and feed efficiency (FE) (P = 0.002) were significantly lower in fish fed the T36 and T36K diets than in those fed the other diets. However, there were no significant differences in final mean weight (P = 0.088), SGR (P = 0.314) and FE (P = 0.829) in fish fed diets T21, T13, T21K and T13K compared to the control diet. Although there were no significant differences in the digestibility of protein (P = 0.076) and energy (P = 0.066) among the treatments, the productive values of protein (P = 0.002) and energy (P = 0.001) were significantly reduced in fish fed the T36 and T36K diets. In contrast, a significantly lower phosphorus (P) retention efficiency (P = 0.026) in fish fed the control diet resulted in significantly higher P discharge (P = 0.001) to the environment compared with diets T21, T13, T21K and T13K. There were no major variations in hematocrit level or plasma constituents among the treatments, except glutamic oxaloacetic transaminase (GOT) and triglyceride. The results suggest that the reduction in TI activity at ≤21 TIU/mg sample (≤9.66 TIU/mg diet) in SPC from soymilk made it possible to replace 80% of FM protein without affecting growth performance and health status. Moreover, a significant reduction in P discharge suggests that ecological benefits can be achieved through improving diet utility by reducing TI activity in SPCs derived from soymilk.

Two trials were carried out to determine the optimal replacement level of fish meal (FM) by soy protein concentrate (SPC) derived from soymilk without supplementation of indispensable amino acids (IAAs) or palatability enhancers and whether phytase supplementation can help to replace more SPC in diet of juvenile red sea bream, Pagrus major. In Trial 1, five isoenergetic diets were formulated: 67% FM as protein source in the control diet (C), and FM was replaced by 60 (SPC60), 70 (SPC70), 80 (SPC80) and 100% (SPC100) by SPC. In Trial 2, diets C and SPC80 were the same as in Trial 1, and phytase was supplemented in SPC80 at 1000 (P1), 2000 (P2), 3000 (P3) and 4000 (P4) FTU/kg diet. Thirty (ca. 23 g) and 20 fish (ca. 21 g) were randomly distributed into each fifteen and eighteen 300 L indoor tanks in Trial 1 and 2, respectively. Fish in both trials were fed two times daily until apparent satiation for 10 weeks. At the end of both trials, feces were collected after feeding with chromic oxide (Cr 2 O 3 ) mixed diets. In Trial 1, there were no significant differences in final mean weight, specific growth rate (SGR), daily feeding rate (DFR), feed efficiency (FE), condition factor (CF), and retention efficiency of protein, lipid and energy until 70% (SPC70) FM replacement by SPC (P >.05). However, 80% FM replacement significantly reduced final mean weight, FE and lipid retention efficiency compared with group C (P <.05). There were no significant differences in plasma constituents, except total cholesterol level. In Trial 2, phytase was supplemented in SPC80 to determine whether it helps to stimulate growth up to the level of the control group. Fish fed SPC80 once again displayed significantly lower final mean weight, SGR, FE, phosphorus (P) digestibility, and retention efficiency of protein, lipid, energy and P compared with control group (P >.05). Final mean weight, FE, P digestibility, and retention efficiency of protein, lipid and P were significantly improved in fish fed diet P2 (phytase at 2000 FTU/kg diet) compared with those fed diet SPC80. However, phytase supplementation did not stimulate the growth up to the level of group C. The results demonstrated in juvenile red sea bream that 70% of FM can be replaced by SPC derived from soymilk without supplementation of IAAs and palatability enhancers.

RNA, DNA, and protein contents were assessed to evaluate somatic growth in larval and juvenile yellowfin tuna (YFT), Thunnus albacares. The experimental fish were reared at the Achotines Laboratory of the Inter-American Tropical Tuna Commission in Los Santos Province, Republic of Panama. Sampling was carried out from 3 to 33 days after hatching (DAH). Standard length and dry body weight rapidly increased from 15 to 17 DAH (flexion-postflexion phase). The RNA-DNA ratio, which indirectly reflects the potential for protein synthesis in larval and juvenile fish, rapidly increased from 17 to 22 DAH (postflexion phase). This suggests that protein synthesis increased at some point between 17 and 22 DAH to induce organ and tissue differentiation. The protein-DNA ratio also rapidly increased from 17 to 22 DAH (postflexion phase), indicating an increase in cell volume. The protein-DNA ratio remained constant between 22 and 33 DAH (early juvenile phase). During this period, the RNA-DNA ratio also remained high, suggesting that the observed growth in the early juvenile phase was due to both increasing cell numbers and cell volume. Thus, active somatic growth was observed from the postflexion phase onwards, contributing to increasing cell numbers, cell volume, and protein synthesis.

It is important to understand the physiological stress responses in juvenile Pacific bluefin tuna (PBF), Thunnus orientalis, when transporting them from land-based tanks to sea cages, to develop countermeasures against mass mortality and enhance survival. We investigated the estimated time required to recover from transportation stress in PBF juveniles (32 and 35 days post hatch (DPH)) transported over two different distances (Exp 1; long distance (15.2 km), Exp 2; short distance (2.3 km)). Additionally, we examined the effects of simulated transport in fish that were transported from tank-to-tank, as well as starvation tolerance to determine the causes of stress responses during transportation. Whole-body cortisol levels and HIF-1α expression levels in gills increased from pre-transport levels shortly after juveniles were released into the sea cage in Exp 1, but recovered within 24 h. Simultaneously, whole-body glucose levels fell over the 48 h after transport. Gene expression of the Hsp70 family in the liver was upregulated 48 h after fish were released into the sea cages in Exp 1, and was significantly upregulated after 48 h in Exp 2. These results indicated that 72 h were required for PBF juveniles to recover from transportation to sea cages. The starvation experiment suggested that PBF juveniles were significantly affected after 2 days of fasting and that the environmental conditions in the sea cage were the main factors resulting in a decrease in whole-body glucose levels and upregulation of Hsp70-family gene expression. Furthermore, changes of proximate compositions indicated that PBF juveniles consumed crude lipids and proteins, which were significantly affected by fasting for 1–2 days. We suggested that the first 3 days after stocking are a critical period for recovery from transportation stress and it is necessary to develop appropriate management techniques to alleviate the high mortality caused by these stress responses.

Hybrid grouper juveniles (body weight, 6.1 ± 0.7 g) (brown-marbled grouper, Epinephelus fuscoguttatus × giant grouper, E. lanceolatus) were fed with six isoproteic (50% crude protein) and isolipidic (12% crude lipid) feeds containing different levels of soy protein concentrate (SPC) in replacement of fish meal (SPC at 20%, 30%, 40%, 50% and 60% protein) and control feed (SPC0) for 6 weeks. Hybrid grouper juveniles were cultured in 100-L fibreglass tank equipped with flow-through water system and fed twice a day to apparent satiation level. The highest and lowest growth was recorded in fish fed SPC20 and SPC60 respectively. However, growth of SPC20 was not significantly higher than those fed SPC0, SPC30, SPC40 and SPC50 (p > .05). A decreasing growth trend was observed with the increasing level of SPC from feed SPC40 to SPC60. A noticeable better feed utilization was also observed in fish fed SPC0, SPC20, SPC30, SPC40 and SPC50 compared to fish fed SPC60 (p < .05). The fish condition factor, hepatosomatic index, viscerosomatic index and whole body proximate content of the fish were not affected by the graded levels of SPC. However, the body lipid content was significantly lower in fish fed SPC40 to SPC60 (p < .05). The apparent digestibility coefficient (ADC) of protein and lipid was significantly higher in fish fed SPC0 and SPC20 compared to other dietary treatments (p < .05). Based on the regression analysis on specific growth rate, the study suggests that the hybrid grouper grow best at 21.4% and can utilize up to 50% inclusion level of SPC in protein without significantly affect their growth and its body condition.

Six isoenergetic diets were formulated as follows: fish meal (FM) 700 g kg–1 (control, C), FM 300 g kg–1 + soy protein concentrate 300 g kg–1 (SPC), FM 300 g kg–1 + enzyme-treated SPC 300 g kg–1 (ESC), FM 170 g kg–1 + soy protein isolate 300 g kg–1 (SPI), FM 160 g kg–1 + enzyme-treated SPI 300 g kg–1 (ESI) and FM 150 g kg–1 + conglycinin 300 g kg–1(CG). Forty fish (3.9 g) were randomly distributed into each of eighteen 300-L tanks, fed twice daily until satiation for 8 weeks. The final body weight, specific growth rate and condition factor did not show significant differences among the fish fed with diets C, SPC, ESC and ESI (p > .05). The survival was significantly lower in fish fed with diets SPI and CG. Feed efficiency was significantly higher in fish fed with diets SPC and C than in fish fed with other diets (p < .05). There were no significant differences in nutrients retention efficiencies in fish fed with diets C, SPC, ESC and ESI. A significantly higher phosphorus retention efficiency in fish fed with soymilk protein diets resulted in lower phosphorus discharge to the environment (p < .05). These results suggest that the soymilk proteins can comfortably replace 570–770 g FM kg–1 diet of red sea bream juvenile, which will ensure significant ecological benefits through reducing phosphorus load to the environment.