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Benefits chitosan-fermented feed additives (CFFAs) particularly in the regulation of the immune system and antimicrobial activity. Therefore, we investigated the immune-enhancing and bacterial clearance effects of CFFA (fermented by Bacillus licheniformis) on broiler chickens Salmonella Gallinarum challenge. We administered 2% or 4% CFFA evaluated its immune-enhancing effects using several immunological experiments, including examination of lysozyme activity, lymphocyte proliferation, and expression of cytokines. We also evaluated the bacterial clearance effects of CFFA against S. Gallinarum. CFFA administration markedly enhanced lysozyme activity, lymphocyte proliferation, and the expression of interleukin (IL)-2, IL-12, tumor necrosis factor alpha, and interferon gamma in the spleen. In broilers challenged with S. Gallinarum, the clinical signs of S. Gallinarum infection and the number of viable bacterial colonies in the feces and tissues decreased in both CFFA groups. Therefore, CFFAs could be good candidates for feed additive to improve nonspecific immune responses and bacterial clearance.

Abstract This study presents a novel permeameter design for field falling-head tests to determine vertical hydraulic conductivity (K) using Darcy's equation. The design features an open-ended standpipe with two ports for simultaneous measurement of hydraulic heads at both ends of the sediment column, enabling direct estimation of flow rate (q) and hydraulic gradient (i). Flow rate is calculated by differentiating the best-fit curve for water level change above the sediment, and the hydraulic gradient is derived from the head difference between the ports. Laboratory and field tests consistently demonstrated a strong linear relationship between q and i (R 2 > 0.999), validating the applicability of Darcy's equation for this new permeameter design. The K values obtained using the proposed method matched those obtained using the Hvorslev equation method. Furthermore, the design allows for continuous measurement of heads after the falling-head permeameter test, facilitating the collection of time series data for the hydraulic gradient. When combined with a pre-determined K value, this enables calculation of time series for the seepage rate across the surface water/sediment interface. To demonstrate this capability, preliminary tests were conducted using commercially-available pressure transducers to monitor heads and obtain seepage time series. The results of these tests are also presented.

A 10-week feeding trial was conducted to evaluate the effects of different feeding rates on growth performance, nutrient deposition, plasma metabolite, and immunity of juvenile starry flounder. Fish (initial mean body weight, 183.6 ± 2.3 g) were subjected to eight feeding rates (0.4, 0.8, 1.2, 1.6, 2.0, 2.4, 2.8, and 3.2% body weight/day [BW/d]) with a commercial diet containing 53.5% crude protein and 10.2% crude lipid. After the feeding trial, fish growth increased significantly (p < 0.05) from 0.4% to 2.0% BW/d, with no significant differences being observed beyond 2.0% BW/d. Protein and lipid gains in the whole body and liver of the fish fed 2.0–3.2% BW/d were significantly (p < 0.05) higher than those of the fish fed 0.4% and 0.8% BW/d. Conversely, protein retention in the whole body and the liver decreased with an increased feeding rate. Lysozyme activity was significantly (p < 0.05) higher in the fish fed 1.6–2.8% BW/d than in those fed 0.4–1.2% BW/d. The best-fit model analyses for optimum feeding rate (OFR) revealed that the estimate for each parameter varied between 0.7% (feed conversion ratio) and 3.1% (lipid gain in carcass) BW/d. The OFR for productivity (weight gain) and enhanced innate immunity (lysozyme) were estimated at 2.4% and 1.7% BW/d, respectively.

Butylated hydroxytoluene (BHT) is a commonly used antioxidant added to animal/fish feed to limit lipid autoxidation and peroxidation. Although there have been reviews and reports of BHT toxicity in animals, limited information is available with respect to the toxic effects and accumulation of BHT due to oral exposure in aquaculture species. Therefore, 120 days of feeding trial was conducted to evaluate the effects of dietary BHT on the marine fish olive flounder Paralichthys olivaceus. Graded levels of BHT were added to the basal diet in increments of 0, 10, 20, 40, 80, and 160 mg BHT/kg, corresponding to 0 (BHT0), 11 (BHT11), 19 (BHT19), 35 (BHT35), 85 (BHT85), and 121 (BHT121) mg BHT/kg diets, respectively. Fish with an average weight of 77.5±0.3 g (mean±SD) were fed one of the six experimental diets in triplicate groups. Growth performance, feed utilization, and survival rate were not significantly affected by the dietary BHT levels among all experimental groups, whereas BHT concentration in the muscle tissue was found to increase in a dose-dependent manner up to 60 days of the experimental period. Thereafter, BHT accumulation in muscle tissue showed a declining trend among all treatment groups. Furthermore, the whole-body proximate composition, nonspecific immune responses, and hematological parameters (except triglycerides) were not significantly influenced by the dietary levels of BHT. Blood triglyceride content was significantly higher in fish fed the BHT-free diet compared to all other treatment groups. Thus, this study demonstrates that dietary BHT (up to 121 mg/kg) is a safe and effective antioxidant without exhibiting any adverse effects on the growth performance, body composition, and immune responses in the marine fish olive flounder, P. olivaceus.

A 12-week feeding trial was designed to evaluate the potential of mealworm, Tenebrio molitor, meal (MW) as a locally available unconventional alternative source of protein for fish meal (FM) in a practical diet for juvenile black porgy. Five hundred twenty-five healthy fish (initial weight; 6.43 ± 0.00 g) were randomly distributed into five dietary groups in triplicate (35 fish per tank) and each group was hand-fed with one of the experimental diets containing graded level of a MW replacing 0%, 15%, 30%, 45%, and 60% of FM protein designated as MW0, MW15, MW30, MW45, and MW60, respectively. Although replacing 60% of dietary FM protein resulted in lower daily feed intake, juvenile porgies fed the highest level of dietary MW (MW60) still performed as well as control group (MW0). A significant negative trend was detected between fillet lipid content and increasing inclusion levels of MW in the diets. There was a notable reduction in the n-3 highly unsaturated fatty acids (HUFA) in the fillets of fish fed the MW containing diets, which became more prominent with greater levels of dietary FM replacement. Serum lysozyme activity improved with increasing inclusion levels of MW in the diet. Furthermore, expression of the antioxidant enzyme-related genes including glutathione peroxidase (GPx) and catalase (CAT) were markedly upregulated in liver of the fish fed diets replacing FM with MW when compared to fish fed the MW0 diet. Overall, the efficacy of MW as a promising alternative dietary protein source for juvenile black porgy has been proved not only in relation to weight gain and efficiency of feed utilization, but also the view point of health-promoting effects in fish.

This study was conducted to investigate the effects of dietary squid liver powder (SLP) content on the growth performance, cadmium accumulation, and non-specific immune response in juvenile olive flounder. The experimental diets included the control diet (S0) without addition of SLP and 5 different treatments which contained 3.9 % (S3.9), 12.0 % (S12.0), 20.1 % (S20.1), 36.2 % (S36.2), and 52.3 % (S52.3) dietary SLP with the final cadmium concentrations of 0.4, 0.8, 1.7, 2.5, 4.6, and 6.4 mg kg−1 diet, respectively. For feeding trial, seven hundred twenty fish (initial weight of 55 g) were randomly distributed into six dietary groups in triplicates (40 fish per tank). At Week 1, 2, 4, 6, and 8 (the end) of the trial, 2 fish were collected from each tank for cadmium content determination. There was no significant difference in survival between all the experimental diets. Weight gain and feed efficiency of fish significantly increased in the fish fed S52.3 compared to the other treatments. Cadmium contents in the viscera including liver significantly increased as dietary SPL content goes up at all analyses from Week 1 to 8. On the contrary, the whole body excluding viscera showed no significant difference in the cadmium content between the experimental diets, and cadmium contents in the whole body were measured below 0.08 mg kg−1 in all the experimental groups at all times of analysis during the 8 week experiment. Superoxide dismutase and lysozyme activities in the fish plasma were significantly affected by dietary SLP contents. It could be concluded that cadmium accumulation in body (excluded the viscera and liver) of juvenile olive flounder fed with SLP-containing diets up to 8 weeks does not raise an issue related to food safety.

This study examined the digestive physiological response of juvenile and growing olive flounder (Paralichthys olivaceus) fed low-fishmeal diets. P. olivaceus (mean initial weight: 7.86 g) were cultured in eight square concrete tanks (10 × 10 m) at a commercial fish farm and fed twice a day with four types of experimental feed (FM70 control, 70% fishmeal content; FM45, 45% fishmeal content; FM35A, 35% fishmeal content; FM35B, 35% fishmeal content + 7% insect meal + 1% insect oil) for 6 months. During feeding experiments, fish growth was observed at 2-month intervals, and digestive organs (stomach, intestine, and liver) were sampled. Organs were stained with hematoxylin/eosin and Alcian blue/periodic acid–Schiff’s solution for each intestinal tissue (pore intestine and pylori), cholecystokinin in the pylori, and pancreatic polypeptide expression in the liver. Trypsin, chymotrypsin, and lipase activities in the intestine were measured. No significant differences in any of the measured variables were observed among the control, FM45, FM35A, and FM35B treatments at any of the sampling intervals. These results suggest that a diet comprising 35% fishmeal with added insects will not affect the digestive physiology of P. olivaceus in commercial fish farming in Korea.

An 8-week feeding trial was designed to evaluate the potential of mealworm (Tenebrio molitor) as a locally available unconventional source of protein in a practical diet for olive flounder (Paralichthys olivaceus). Three hundred juveniles (initial weight, 33.5 ± 0.01 g) were randomly distributed into five dietary groups in triplicate (20 fish per tank), and each group was hand-fed one of the experimental diets containing a graded level of a mealworm meal (MW) replacing 0, 20, 40, 60, and 80 % of fish meal (FM) protein (designated as MW0, MW20, MW40, MW60, and MW80). The specific growth rates of juvenile flounders revealed a decreasing trend with increasing dietary MW levels. However, feed utilization efficiency tended to improve with the increasing percentage of dietary FM replacement up to 40 % but gradually decreased in higher replacement levels. The results displayed a linear and quadratic negative effect of dietary MW inclusion level on nutrient digestibility. A significant negative linear trend was detected between dietary MW content and plasma total cholesterol. Except for lipid content, which displayed a significant decreasing trend as the dietary MW content increased, no other changes were evident in the fillet proximate composition. Significant positive linear and quadratic trends were observed between fillet C18:1n-9 (oleic acid; OA) and C18:2n-6 (linoleic acid; LA) levels and dietary MW content, where the OA and LA values increased in a dose-dependent manner. The fillet Σn3 / Σn6 ratio and atherogenic index demonstrated significant decreasing trends with dietary inclusion of MW while the fillet thrombogenic index and hypocholesterolaemic/hypercholesterolaemic fatty acid ratio exhibited significant positive trends with increasing values. Myeloperoxidase activity declined with replacement of up to 40 % FM protein but thereafter gradually increased at higher replacement levels. Glutathione peroxidase activity generally was enhanced with increasing dietary MW inclusion. Dietary MW inclusion had no significant impact on the bacterial community of the juvenile flounder’s hindgut. Although replacing up to 80 % of FM with MW may promote an immunostimulatory effect, in order to avoid unfavorable effects on feed efficiency and nutritional value of the fillet lipid fraction no more than 40 % of FM is recommended to be replaced by a MW in diets for olive flounder juveniles. Our findings could promote the utilization of MW in olive flounder feed, which may not only reduce dependence on high priced and finite feed ingredients, but also enhance farmed fish health status.

Abstract This study was conducted to evaluate the use of tuna by-product meal (TBM) as a substitute for fishmeal in juvenile Korean rockfish (Sebastes schlegeli) diets. Five isonitrogenous (52% crude protein) and isocaloric (4.9 kcal/g) diets were prepared. Control diet (Con) was formulated to contain brown fishmeal, whereas 25, 50, 75, and 100% of fishmeal was substituted with the same percentage of TBM in the TBM25, TBM50, TBM75, and TBM100 diets, respectively. Three replicate groups of fish (initial weight, 29.5 ± 0.6 g) were fed one of the five diets for 12 weeks. The mean weight gain of fish fed the Con and TBM25 diets was significantly higher than that of fish fed the TBM100 diet (P

Abstract In recent years, Bacillus spp. have garnered attention as probiotic supplements in aquafeed owing to the production of heat stable and low pH resistant spores. Herein, we isolated and characterized an autochthonous Bacillus licheniformis KCCM 43270 from the intestine of olive flounder (Paralichthys olivaceus) for supplementation in low‐fishmeal extruded aquafeeds. The KCCM 43270 was screened based on amylase, protease, cellulase, and lipase as well as non‐hemolytic activities. The isolate was able to grow in carboxymethyl cellulose (CMC), xylan, and soybean meal (SBM) when used as a single carbon source in the minimal nutrient M9 medium. The KCCM 43270 spores displayed complete survival in acid (pH 2.5) and bile (0.3%, w/v) for 3 hr, strong biofilm formation, and nearly 50% adhesion with intestinal mucus. The spores of the isolate also showed significant survival ability at 80, 90, 100°C for 60, 30, and 1 min, respectively. In addition, the spores in a blend of SBM complex carrier showed significant heat stability at 120°C for 5 min and under different drying conditions. Furthermore, the spores also survived the extrusion process during low‐fishmeal aquafeed manufacturing, implying the potential application of B. licheniformis KCCM 43270 in aquafeed industry.

Olive flounder (Paralichthys olivaceus) is a commercially important and valuable species for aquaculture in Korea. Due to the unstable supply of fishmeal for farmed fish, an optimum fish-feed formulation should be researched to ensure the sustainability of P. olivaceus aquaculture. This study investigated the effect of three experimental diets: Con (basal diet); FM20 (20% fishmeal replacement of CON); and FM30 (30% fishmeal replacement of CON) on P. olivaceus over 20 weeks at a typical farm by monitoring the growth and factors relating to sexual maturation. The results showed that no differences in growth were observed between the CON and diet-replacement groups. Gonadal oocyte development was similar between the CON and diet-replacement groups. Moreover, sbGnRH and GH expression did not differ between the CON and diet-replacement groups. The levels of Erβ and Vtg expression were significantly higher in the FM20 group than in the CON and FM30 groups after the experimental period. The expression of PSS-I was significantly higher in the FM30 group than in the CON and FM20 groups. Therefore, although growth occurred when 30% of the fishmeal was replaced, such high dietary protein replacement may be ill-advised during the maturation of olive flounder at the commercial fish farm.

Abstract Apparent digestibility coefficients (ADCs) of dry matter, crude protein, crude lipid, energy, essential amino acids, and fatty acids in extruded pellets containing various fish meals were determined for olive flounder (Paralichthys olivaceus). Eight extruded pellet diets were prepared to contain different fish meals (herring fish meal, anchovy fish meal, mackerel fish meal, sardine fish meal-A, sardine fish meal-B, tuna fish meal, pollock fish meal-A, and pollock fish meal-B) designated as HM, AM, MM, SM-A, SM-B, TM, PM-A, and PM-B, respectively. Chromic oxide (Cr2O3) was used as an inert indicator at a concentration of 0.5 % in the diet. Feces were collected from triplicate groups of fish (151 ± 4.0 g) using a fecal collection column attached to the fish rearing tank for 4 weeks. Dry matter ADCs of the MM, SM-A, SM-B, and PM-A diets were higher than those of all the other dietary groups, and the lowest digestibility of dry matter was observed in the PM-B diet. Fish fed the MM, SM-A, and PM-A diets showed significantly higher ADC of protein than those fed the AM, SM-B, TM, and PM-B diets. Lipid ADC of PM-B was significantly lower than that of the other diets. Energy ADCs of fish fed the MM, SM-A, and PM-A diets were significantly higher than those of the other diets. The availability of essential amino acids in the MM, SM-A, and PM-A diets were generally higher than that of the other fish meal diets, while TM showed the lowest values among all the experimental diets. ADCs of fatty acids in the AM, MM, SM-A, and PM-A diets were generally higher than those of fatty acids in the other diets, and the lowest values were recorded for the PM-B diet. These results provide information on the bioavailability of nutrients and energy in various fish meals which can be used to properly formulate practical extruded feeds for olive flounder.

The objective of this study was to conduct field experiments comparing formulated (extruded pellets (E.P)) and raw-fish (moist pellets (M.P)) feeds at two flounder aquaculture farms for six months to obtain the basic data necessary for improving aquafarmers’ awareness of feed-quality issues and firmly establish and expand the use of formulated feed. According to the results, the M.P group was higher in weight gain, feed efficiency ratio, protein efficiency ratio, and specific growth rate and lower in mortality rate than the E.P group. All cases of mortality were caused by six kinds of disease, four of which (Vibrio sp., Edwardsiella sp., Streptococcus sp., and Scuticociliates) were common to the two groups, whereas Lymphocystis arose only in the M.P group and abdominal inflation only in the E.P group at both farms. As for mortality in the present experiment, the numbers were 1047 at Da-Hae farm and 1167 at Global farm, with more fish dying in the E.P tanks than in the M.P tanks. By multiplying the number of deaths by selling price, the economic losses were $9650 and $10,756, respectively. Therefore, it should be considered an urgent priority to develop flounder-exclusive formulated feed for improved digestion and absorption rate and also to establish a water-quality-improvement management plan.