Juvenile Yellowtail Research Articles

The combination effect of N-acetyl-d-glucosamine on oral oxytetracycline treatment against Nocardia seriolae infection in the yellowtail Seriola quinqueradiata

Nocardia seriolae infection is one of the most serious bacterial diseases in Seriola species in Japanese aquaculture. In this study, the combination effect of N-acetyl-d-glucosamine (NAG) with oral oxytetracycline (OTC) treatment was evaluated with the experimental infection of artificially bred juvenile yellowtail Seriola quinqueradiata. Prior to the evaluation, the efficacy of OTC treatment against nocardiosis was assessed. The oral administration of OTC at a dose of 50mg/kg body weight (BW) for 4 consecutive days did not show sufficient efficacy compared with that of the untreated control group, while the intraperitoneal administration of OTC, which caused no absorption loss in the gastrointestinal tract at a single dose of 50mg/kg BW successfully suppressed mortality (P<0.05). When OTC was orally administered with the same amount of NAG at a single dose of 50mg/kg BW, the serum OTC concentrations significantly increased at 1h and 6h post-administration (P<0.05); peak concentrations increased by 41%. In two trials evaluating the treatment of nocardiosis, the addition of NAG improved the efficacy of 5-consecutive-day oral OTC treatment by significantly reducing mortality compared with that of the untreated control group (P<0.05). These results suggest that NAG can enhance the absorption of oral OTC and therefore improve the efficacy of nocardiosis treatment.

Use of marine by-product meals in diets for juvenile longfin yellowtailSeriola rivoliana

A 60-day feeding trial to determine the nutritional value of marine by-product meals in diets for longfin yellowtail Seriola rivoliana juveniles (48.1 ± 0.6 g initial weight) was conducted. Five diets were evaluated: a reference diet (RD; 500 g kg−1 CP, 130 g kg−1 L), containing 500 g kg−1 of fish meal (FM); three experimental diets with 125 g kg−1 of shrimp head (SM), Catarina scallop viscera (CM) or Pen shell viscera (PM) meals; and one diet (SCP) containing 125 g kg−1 of each of the experimental meals, to partially replace FM. Survival was not significantly affected by any treatment. Individual weight gain per day was high for the PM (5.3 ± 0.51 g d−1) and SM (4.7 ± 0.32 g d−1) diets, being significantly higher than the RD (3.5 ± 0.23 g d−1) and the other treatments (<1.2 g d−1). Feed intake was high in PM and SM diets, and very low in SCP and CM diets. Biochemical and haematological parameters were similar among treatments RD, PM and SM, while fish fed CM and SCP exhibited lower levels of total protein, cholesterol, haematocrit and haemoglobin. The results indicate that SM or PM can be used to partially replace FM in diets for yellowtail juveniles.

Effects of replacing fish oil with canola oil on the growth performance, fatty acid composition and metabolic enzyme activity of juvenile yellowtail Seriola quinqueradiata (Temminck &amp; Schlegel, 1845)

In this study, fish oil (FO) was replaced with canola oil (CO) in juvenile yellowtail diets to establish the optimal replacement levels that ensure adequate feed quality for aquaculture. Juvenile yellowtails (initial body weight: 104.7 g) were fed one of four diets for 10 weeks: 100% FO (FO group) or FO replacement with 25%, 50% or 100% CO (CO25, CO50 and CO100 groups respectively). Body weight, specific growth rate and feed efficiency were significantly affected by the replacement of FO with CO. The final body weight of the CO100 group was significantly lower than that of the FO (control) and CO50 groups. Furthermore, the CO50 group showed significantly higher feed efficiency than the FO group during the first 4 weeks (long photoperiod and high water temperature conditions). Increasing dietary CO increased serum glucose and triglyceride concentrations in a dose-dependent manner. Regarding the proximate composition of fillet and liver, only crude protein in fillet was affected by the replacement of FO with CO. Fatty acid compositions of fillet and liver were correlated to the amount of CO in each diet. The activities of the metabolic enzymes phosphofructokinase and alanine aminotransferase were lowest in the CO25 and CO50 groups respectively. Thus, FO replacement with CO affected growth performance, serum components, fatty acid composition and the activity of metabolic enzymes. Overall, results obtained in the present study suggest that partial replacement (50%) of FO with CO is effective and might increase juvenile yellowtail growth under long photoperiod and/or high water temperature conditions.

한국 남해안에 출현하는 방어(Seriola quinqueradiata) 치어 및 유어의 식성

한국 남해안에 출현하는 방어(Seriola quinqueradiata) 치어 및 유어의 식성

Morphological Development of Embryo, Larvae and Juvenile in Yellowtail Kingfish, Seriola lalandi.

This study monitored the morphological development of embryo, larvae and juvenile yellowtail kingfish, Seriola lalandi, for their aquaculture. The fertilized eggs obtained by natural spawning were spherical shape and buoyant. Fertilized eggs were transparent and had one oil globule in the yolk, with an egg diameter of 1.35 ± 0.04 mm and an oil globule diameter of 0.32 ± 0.02 mm. The fertilized eggs hatched 67–75 h after fertilization in water at 20 ± 0.5°C. The total length (TL) of the hatched larvae was 3.62 ± 0.16 mm. During hatching, the larvae, with their mouth and anus not yet opened. The yolk was completely absorbed 3 days after hatching (DAH), while the TL of post-larvae was 4.72 ± 0.07 mm. At 40 DAH, the juveniles had grown to 30.44 ± 4.07 mm in TL, body depth increased, the body color changed to a black, yellow, and light gray-blue color, and 3–4 vertical stripes appeared. At 45 DAH, the juveniles were 38.67 ± 5.65 mm in TL and 10.10 ± 0.94 mm in body depth. The fish were green with a light orange color, with 7 faint green-brown stripes on the sides of their body. At 87 DAH, the juveniles had grown to 236.11 mm in TL, 217.68 mm in fork length, and 136.5 g in weight. The fish resembled their adult form, with a light yellow-green body color, loss of the pattern on the sides of their body, and a yellow coloration at the tip of the caudal fin.

Growth, antioxidant capacity and muscle histochemistry of yellowtail kingfish (Seriola lalandi Valenciennes 1883): Selenium and temperature interaction

The aim of this study was to investigate the interactive effects of temperature and dietary selenium concentrations on antioxidant capacity, muscle histochemistry and the growth, of juvenile yellowtail kingfish (Seriola lalandi). The yellowtail kingfish were exposed to two temperatures (21°C or 26°C) and three selenium levels (0.0, 2.0 or 4.0mgSekg−1 of feed) for 30 days. Final weight and specific growth rate (SGR) were significantly affected by water temperature (ρ<0.001) and dietary Se (ρ<0.001) supplementation, and there were significant differences in the interaction between these two factors. Juvenile yellowtail kingfish fed Se-supplemented diets, attained a higher final weight and SGR than those without Se supplementation at 21°C, but not at 26°C. Regardless of the temperature, the red blood cell (RBC) glutathione peroxidase (GPx) activity of yellowtail kingfish fed Se-supplemented diets was significantly higher (ρ<0.05) than with the control diet. However, GPx activity of yellowtail kingfish when fed either 2.0mgSekg−1 or 4.0mgSekg−1 showed no significant difference (ρ>0.05). Se concentration in the muscles of juvenile yellowtail kingfish fed Se-supplemented diets was higher than that of the yellowtail kingfish that were fed the control diet. A histopathological test confirmed that 20.3% of fish muscles exhibited lesions, which occurred in the absence of dietary Se. The outcome of the present study helps in understanding the interactive effects of dietary Se concentrations and the temperature in the farming of yellowtail kingfish.

Use of Organic Selenium Supplements in Soybean Meal- Based Diets for Juvenile Yellowtail Kingfish (Seriolalalandi)

Sustainable aquaculture, from both ecological and economic perspectives, demands a substantial reduction of the amount of fishmeal used in aqua feed. Instead, plant-derived protein feed stuff, which provide a nutritious diet offer a promising alternative for inclusion in aqua feed. In this study, the effects of organic selenium supplementation in low and high soybean meal-based practical diets for yellowtail kingfish (Seriola lalandi) were evaluated over a 60-day feeding experiment. The juvenile yellowtail kingfish (initial weight 5.02 ± 0.04 g fish −1 ) were fed five iso-nitrogenous and iso-caloric diets containing 49% crude protein and 22 MJ kg −1 gross energy. The control diet(C) includes 46% fishmeal, whereas the other diets used soybean meal to replace 25% and 75% of the fishmeal protein, both without and with organic selenium supplementation (SBM 25 , SBM 25+Se , SBM 75 , and SBM 75+Se ). Fish were fed ad libitum two times a day at 09:00 and 15:00 hours. No differences were observed in feed intake among dietary treatment groups (P > 0.05). Organic selenium-supplemented diets improved final weight; however, final weight was significantly reduced when fish were fed high soybean meal diets (P < 0.05). Organic selenium supplementation had a significant effect on specific growth rate at low soybean meal diets, but did not affect specific growth rate when fish were fed high soybean meal diets. Selenium accumulation in fish fillet was strongly correlated with selenium concentration in the diets. While fish fed the SBM 25+Se diets had significantly higher glutathione peroxidase activity than those fed other diets, the lowest glutathione peroxidase activity was found in fish fed SBM 75 diets. Histologically, selenium-deficient diets induced myopathy and alterations in tissue structure were most prevalent in fish fed the SBM 75 diet. The findings of this study indicate that, with Se supplementation, soybean meal could supply 25% of the protein in yellowtail kingfish diets.

Beneficial utilization of a tuna processing by-product as fish-feed additive

During tuna processing for human consumption, the fish are initially boiled in water, creating ~7000 tons of wastewater a year in Tosashimizu City, Japan. The wastewater (tuna broth; TB) is rich in free amino acids and peptides; therefore, we investigated two methods of utilizing it beneficially. In experiment 1, crude TB was used as a growth enhancer for two farmed species, juvenile yellowtail (Seriola quinqueradiata) and red sea bream (Pagrus major). Juveniles of both species, fed commercial extruded pellets mixed with 300 mL TB, showed significantly better growth than the unsupplemented control group. In experiment 2, concentrated TB was used as a dietary ingredient for juvenile yellowtail to improve palatability and growth. Dietary preferences and growth were rated as follows: fish meal diet > soy protein concentrate (SPC) + TB diet > SPC + krill meal diet > SPC diet. The beneficial effects of TB as a dietary supplement were evident. Crude TB enhanced juvenile growth at minimal cost. Concentrated TB requires processing, with associated costs; however, it proved to be a valuable fish-feed supplement because of its high palatability and growth-promoting effect. The utilization of TB also contributes to reducing the environmental impact of fish wastewater.

Effect of dietary cholesterol content on growth and its accumulation in liver and muscle tissues of juvenile yellowtail kingfish (Seriola lalandi)

A feed trial conducted with juvenile yellowtail kingfish (Seriola lalandi) was designed to address the effect of dietary cholesterol content on growth performance and the cholesterol concentration in liver and muscle. For 60 days fish were fed four diets based on defatted fish meal, soy protein concentrate, cholesterol-free fish oil, canola oil, and olive oil, with four different concentrations of cholesterol (treatments Ch0.0, Ch0.05, Ch0.12, and Ch0.19 containing 530, 2880, 4120, and 6170 mg kg–1 of crude fat, respectively). After 60 days, maximum weight gain was obtained with diet Ch0.05, and it was significantly higher than that obtained with diets Ch0.0 and Ch0.19, but not different from that obtained with Ch0.12. Cholesterol concentration in liver and muscle tissues was not affected by the diet, showing no significant differences among dietary treatments with levels reported as normal. Though cholesterol biosynthesis could not be measured in the present work, we discuss the possibility that fish are able to synthesize cholesterol when fed diets containing no or less cholesterol than required, but at the expense of energy consumption, limiting fish growth. We conclude that cholesterol content in aquafeeds affects fish growth when diets are formulated with vegetable ingredients, and the optimal content should be between 2880 and 4120 mg kg–1 of crude fat to avoid consequent cholesterol accumulation in liver or muscle tissues.

Forced sustained swimming exercise at optimal speed enhances growth of juvenile yellowtail kingfish (Seriola lalandi).

Swimming exercise at optimal speed may optimize growth performance of yellowtail kingfish in a recirculating aquaculture system. Therefore, optimal swimming speeds (Uopt in m s−1 or body lengths s−1, BL s−1) were assessed and then applied to determine the effects of long-term forced and sustained swimming at Uopt on growth performance of juvenile yellowtail kingfish. Uopt was quantified in Blazka-type swim-tunnels for 145, 206, and 311 mm juveniles resulting in values of: (1) 0.70 m s−1 or 4.83 BL s−1, (2) 0.82 m s−1 or 3.25 BL s−1, and (3) 0.85 m s−1 or 2.73 BL s−1. Combined with literature data from larger fish, a relation of Uopt (BL s−1) = 234.07(BL)−0.779 (R2 = 0.9909) was established for this species. Yellowtail kingfish, either forced to perform sustained swimming exercise at an optimal speed of 2.46 BL s−1 (“swimmers”) or allowed to perform spontaneous activity at low water flow (“resters”) in a newly designed 3600 L oval flume (with flow created by an impeller driven by an electric motor), were then compared. At the start of the experiment, ten fish were sampled representing the initial condition. After 18 days, swimmers (n = 23) showed a 92% greater increase in BL and 46% greater increase in BW as compared to resters (n = 23). As both groups were fed equal rations, feed conversion ratio (FCR) for swimmers was 1.21 vs. 1.74 for resters. Doppler ultrasound imaging showed a statistically significant higher blood flow (31%) in the ventral aorta of swimmers vs. resters (44 ± 3 vs. 34 ± 3 mL min−1, respectively, under anesthesia). Thus, growth performance can be rapidly improved by optimal swimming, without larger feed investments.

Limiting Amino Acids in Practical Diets for California Yellowtail, Seriola lalandi

AbstractThree trials were run to identify the limiting dietary amino acids in practical, soy‐based formulations for California yellowtail juveniles. In the first trial, four diets were formulated with 20% fish meal and 43% soy protein concentrate. The basal diet was supplemented with methionine, lysine, and taurine (MLT), and each supplement was then individually deleted in three additional diets (LT, MT, and ML). A significant decrease in growth was only seen in fish fed the ML diet. The second and third trials were designed to test graded levels of dietary taurine and methionine, respectively. Dietary taurine ranged from 0.32 to 1.5%, and methionine levels ranged from 0.95 to 1.19% of the diet with constant levels of cysteine (0.73%). While weight gains were considered adequate to detect a dietary amino acid deficiency, there was no significant effect of graded levels of either taurine or methionine on final weights, growth rates, survival, or feed efficiency. In conclusion, the practical diets tested required taurine supplementations, but did not require lysine or methionine supplementation. While these data are insufficient to determine the taurine or methionine requirement of California yellowtail, it provides minimum levels likely to meet these requirements. Additional research is necessary to determine taurine and methionine requirements precisely in this species.

Hyper-Saline Conditions Affect Growth, Osmoregulation and Survival of Fingerling and Juvenile Yellowtail Kingfish, Seriola Lalandi

Hyper Saline Conditions Affect Growth Osmoregulation and Survival of Fingerling and Juvenile Yellowtail Kingfish Seriola Lalandi

Minimizing fishmeal use in juvenile California yellowtail, Seriola lalandi, diets using non-GM soybeans selectively bred for aquafeeds

A study was undertaken to examine the potential of two non-genetically modified (non-GM) soy products, differentially processed, as fishmeal (FM) replacements. Dietary protein (DP) was replaced at 50, 60 and 70% using the 3011 meal or 40, 50 and 60% with the 3032 meal. Ingredient 3011 was a cooked and solvent-extracted meal from a high protein and low oligosaccharide soy cultivar; whereas, ingredient 3032 was a cold-pressed, low fat cake ground to a meal that originated from a medium protein, low oligosaccharide, low protease inhibitor soy cultivar. Experimental diets were isonitrogenous (45% crude protein, CP), isolipidic (13% lipid), isocaloric (12.6 kJ energy kg− 1 of diet) and were balanced for lysine (3.2%) and methionine + cysteine (2%). Taurine was supplemented at 1.5% in all diets. A commercial control diet (52% CP and 13% lipid) was included for a total of eight test diets. Twenty four round tanks (330 L) were each stocked with 20, 4 g yellowtail (Seriola lalandi). Tanks were supplied with recirculated seawater and each diet was randomly assigned to three replicate tanks. After a 10-week feeding trial, growth, survival, feed conversion ratio, protein efficiency ratio, protein retention, condition factor and carcass proximate composition were contrasted among dietary treatments. Results indicate that juvenile yellowtail fed diets in which the 3032 meal provided 50 and 60% of DP grew significantly (P < 0.001) better than those fed all other diets, including the FM-based (menhaden FM) and commercial control diets. Fish fed with the 3011 meal providing 50% of DP and those fed with the 3032 meal providing 40% of DP had similar growth performance which was slightly greater than the fish fed the FM reference diet. Minor intestinal histology differences were found among fish fed the 8 diets. Taken together these data indicates that the improved non-GM soybean meals supported better performance of juvenile yellowtail than fish fed the FM reference diet. No enteritis was detected even at high dietary inclusion levels.

Dietary branched-chain amino acid supplementation affects growth and hepatic insulin-like growth factor gene expression in yellowtail,Seriola quinqueradiata

We investigated the effect of dietary supplementation with a branched-chain amino acid (BCAA) mixture (valine, leucine and isoleucine) on juvenile yellowtail (Seriola quinqueradiata) growth and hepatic insulin-like growth factor (IGF) gene expression. Total dietary BCAA content was 8.1, 8.5, 9.0 and 9.8 g kg−1 for the control, 0.4%, 1.0% and 2.0% BCAA experimental groups, respectively. Body weight was measured on day 77, after which fish were fasted for 3 days and refed; the livers were then removed 3 or 9 h later for analysis of hepatic gene expression. Body weight significantly increased in the BCAA-supplemented groups. Hepatic expression of IGF1 and IGF2 significantly increased in the 2% BCAA group at 3 and 9 h after refeeding. In the 1% BCAA group, hepatic IGF1 expression tended to be higher at 9 h than in the control group after refeeding. Also, hepatic IGF2 significantly increased at only 9 h after refeeding in the 1% BCAA group. In conclusion, dietary supplementation with crystalline BCAAs increased growth and hepatic expression of IGF1 and IGF2. These results suggest that dietary crystalline BCAA supplementation would be a valuable addition to yellowtail aquaculture practices.

Toxic effects of excessive levels of dietary selenium in juvenile yellowtail kingfish (Seriola lalandi)

Abstract Selenomethionine (SeMet) was supplemented to a fishmeal-based diet to investigate the toxic effects of excessive levels of dietary selenium (Se) in juvenile yellowtail kingfish ( Seriola lalandi ). For 10 weeks, the fish were fed one of five experimental diets; a basal diet containing 2.31 mg/kg of inherent Se or diets supplemented with SeMet to provide 4.91, 9.58, 15.43 or 20.87 mg/kg of Se. The results showed that the fish muscle proximate composition, feed conversion ratio and survival were not sensitive to dietary Se treatments; and no histopathological lesions were observed in heart and intestine tissues of the fish. The Se concentrations in liver and muscle tissues showed a strong linear positive relationship with the levels of Se in diets. Fish when fed the basal diet exhibited Se deficiency symptoms including myopathy, reduced feed intake, glutathione peroxidase activity and growth; whereas those fed the diets containing ≥ 4.91 mg Se/kg did not. While fish fed the 15.43 mg Se/kg diet did not show any toxic effects, the 20.87 mg Se/kg diet caused histopathological changes in liver and spleen as well as reduced feed intake, growth, haematocrit and hepatosomatic index, indicating Se toxicity. In conclusion, Se levels in liver and muscle tissues can be used as effective indicators of dietary Se exposure and dietary Se level between 15.43 and 20.87 mg/kg may be a threshold level in juvenile yellowtail kingfish.

Drifting algae and fish: Implications of tropical Sargassum invasion due to ocean warming in western Japan

Evidence is accumulating that the invasion and extinction of habitat-forming seaweed species alters coastal community structure and ecological services, but their effects on the pelagic environment have been largely ignored. Thus, we examined the seasonal occurrence patterns of indigenous temperate and invasive tropical drifting algae and associated fish species every month for 2 years (2009–2011) in western Japan (Tosa Bay), where a rapid shift from temperate to tropical Sargassum species has been occurring in the coastal area since the late 1980s due to rising seawater temperatures. Of the 19 Sargassum species (31.6%) in drifting algae, we found that six were tropical species, whereas a study in the early 1980s found only one tropical species among 12 species (8.3%), thereby suggesting an increase in the proportion of tropical Sargassum species in drifting algae during the last 30 years. Drifting temperate algae were abundantly present from late winter to summer, whereas tropical algal clumps occurred primarily during summer. In the warm season, fish assemblages did not differ significantly between drifting temperate and tropical algae, suggesting the low host–algal specificity of most fishes. We also found that yellowtail juveniles frequently aggregated with drifting temperate algae from late winter to spring when drifting tropical algae were unavailable. Local fishermen collect these juveniles for use as aquaculture seed stock; therefore, the occurrence of drifting temperate algae in early spring is important for local fisheries. These results suggest that the further extinction of temperate Sargassum spp. may have negative impacts on the pelagic ecosystem and associated regional fisheries.

Plasma Components and Hepatic Insulin‐like Growth Factor Expression Indicate Nutritional Status in Yellowtail Seriola quinqueradiata

AbstractWe examined the effect of feeding ration and refeeding time on plasma biochemical components and hepatic insulin‐like growth factor gene (IGF) mRNA expression to evaluate nutritional indicators in juvenile Yellowtail Seriola quinqueradiata (also known as Buri). Fish were fed a diet for 10 d with the following feeding rations: 80, 40, 20, and 10% satiation. Satiated feeding was 4.65% of body weight. At day 10, the plasma concentrations of albumin, calcium, inorganic phosphate, and total protein, activities of alkaline phosphatase and amylase, and hepatic IGF1 mRNA and IGF2 mRNA expression were significantly correlated with feeding ration. In the analysis of refeeding time, fish were refed after a 24‐h fasting period and plasma biochemical components and hepatic IGFs mRNA were analyzed at 0, 3, 6, and 9 h after refeeding. Plasma concentrations of total bilirubin, inorganic phosphate, creatinine, glucose, and potassium, and activities of amylase were significantly correlated with refeeding time. The correlation between refeeding time and gene expression was significant for IGF2 mRNA (r = 0.70, P &lt; 0.05) but not for IGF1 mRNA (r = 0.67, P = 0.07). Comparing the results of the two experiments, the plasma concentrations of total protein, albumin, and calcium reflected only the feeding ration. The plasma concentration of inorganic phosphate, activities of alkaline phosphatase and amylase, and hepatic IGF1 mRNA and IGF2 mRNA reflected both the feeding ration and refeeding time. These observations suggest that these components reflected the nutritional status of Yellowtail, but sampling time should be carefully examined because of the fluctuating feature of these components.

Quality improvement of fish feed by using insulin-like growth factor 1 as a potential indicator of amino acid deficiency in yellowtail

Abstract We developed a new method for improving the quality of fish feed, by using insulin-like growth factor 1 (IGF1) as a potential indicator of dietary amino acid deficiency in yellowtail ( Seriola quinqueradiata ). First, 7 dispensable amino acid solutions (alanine, asparagine, cysteine, glutamine, glycine, serine and proline) and 0.9% NaCl (control) solution were injected into the dorsal muscle of fish using a syringe. Twenty-four hours post-administration, white muscle tissue was collected from the fish opposite to the injection site and assayed for igf1 mRNA expression. Only fish injected with proline showed a significant increase in igf1 mRNA expression levels. Subsequently, a feeding trial was conducted with 3 different diets—the control diet; the control diet supplemented with 1% proline; and the control diets supplemented with 3% proline. Juvenile yellowtails were fed exclusively with 1 of the 3 diets until apparent satiation. The body weight and feed efficiency were significantly higher in fish fed with the 3% proline-supplemented diet than fish fed with the control diet. Further, after 3 weeks, the expression levels of igf1 in white muscle and liver were significantly higher in fish fed with the 3% proline-supplemented diet than in fish fed with the control diet. Our results suggest that igf1 mRNA expression in the white muscle tissue of yellowtails serves as a reliable indicator of amino acid deficiency. Additionally, the results of our feeding trial suggest that proline is required for juvenile yellowtail growth. Moreover, white muscle igf1 may represent a valuable tool for improving the quality of fish feed.

The use of a soy product in juvenile yellowtail kingfish (Seriola lalandi) feeds at different water temperatures: 2. Soy protein concentrate

Juvenile yellowtail kingfish (Seriola lalandi) were fed four iso-nitrogenous and iso-calorific (digestible basis) experimental diets containing 0, 20, 30 or 40% soy protein concentrate (SPC) for 34days at optimal (22°C) and suboptimal water temperatures (18°C) to measure the responses of growth, feed efficiency, nutrient digestibility, gut histology and digestive enzyme activity to dietary manipulation. The substitution of fish meal with 20% SPC did not significantly affect the growth of fish. However, second-order polynomial regression analyses demonstrated that there was a negative impact on the growth of the fish with increasing inclusions of SPC. By contrast, the feed intake was not affected by SPC inclusion, but the apparent feed conversion ratio was significantly increased (worse) above 30% SPC inclusion. The protein and energy efficiency ratios were significantly reduced above 30% SPC inclusion. The whole body moisture and total fat composition were affected above 20% SPC inclusion, but there was no effect on apparent dietary nutrient digestibilities. Suboptimal water temperature significantly decreased all measured growth performance and feed efficiency variables. By contrast, the protein and energy efficiency ratios were higher at 18°C, while the protein and energy retentions were not affected by temperature. The apparent dietary protein digestibility was influenced by temperature, and its increase at 18°C suggests the influence of a slower gut transit time at the cooler temperature. This study indicates that juvenile yellowtail kingfish can effectively utilise 20% SPC, regardless of water temperature.

Detection of nonylphenol and persistent organic pollutants in fish from the North Pacific Central Gyre

Despite scientific and public concern, research on food web contamination from chemicals in plastic is limited, and distinguishing plastic sources from prey remains a challenge. We analyzed juvenile yellowtail (Seriola lalandi) from the North Pacific Central Gyre for plastic ingestion and tissue concentrations of persistent organic pollutants and nonionic surfactants to investigate potential contamination from plastic exposure. Ingestion of synthetic debris occurred in ∼10% of the sample population. PCBs and DDTs were 352±240 (mean±SD) and 1425±1118ng/g lw, respectively. PBDEs were 9.08±10.6ng/glw, with BDEs-47, 99, and 209 representing 90% of PBDEs. Nonylphenol (NP) was detected in one-third of the yellowtail with a mean of 52.8±88.5ng/g ww overall and 167±72.3ng/g ww excluding non-detects. Because environmental NP is strongly associated with wastewater treatment effluents, long-range transport is unlikely, and NP was previously measured in gyre plastic, we concluded that plastic-mediated exposure best explained our findings of NP in yellowtail.