Response changes with growth in the gustatory receptors of young yellowtails (Seriola quinqueradiata)

SUMMARY: Laboratory-hatched juvenile yellowtails (mean fork length, 9.3 cm) were reared for 2 months in two groups on different kinds of food, mysid and squid in one group and fish in the other, and the gustatory neural responses to seven chemicals (adenosine-5'-monophosphate, alanine, arginine, betaine, proline, tryptophan, and valine) were recorded in fish before and after the 2-month rearing period. Large variances in the responses to some chemicals were noticed in the juveniles before the rearing experiment. Mann–Whitney U -tests on the neural responses indicated significant changes in the magnitude of the responses to valine and some other chemicals relative to that for proline or tryptophan between the pre- and the two post-rearing groups. No significant differences in the response magnitude for the seven chemicals were observed for the two post-rearing groups suggesting that the response changes during the 2-month rearing might have been intrinsic and not due to specific food items in the diet. The dose–response relationship for some chemicals was also examined in the juveniles before and after the 2-month rearing. A slight lowering of threshold was noticed for alanine and valine after the rearing. Data on the responses of wild yellowtails were in support of the changing responsiveness of gustatory receptors during development of juvenile yellowtails.     

Comparison of Collagen Distribution and Muscle Structure Between Cultured Amberjack (Seriola dumerili) and Cultured Yellowtail (Seriola quinqueradiata)

ABSTRACT

The collagen distribution in cultured specimens of amberjack and yellowtail were assessed by histochemical observation in relation to the meat texture of the fish. Major structural alteration was observed in the level of pericellular connective tissue of yellowtail that had higher muscle lipid content; these changes are likely to be associated with the large-scale changes in muscle firmness resulting from the weakening of the cellular binding force. However, lipid deposition was limited to the myocommata in amberjack muscle; lipid deposition was not observed in the pericellular connective tissue, which is the likely reason why amberjack maintained firmer meat texture.     

Experimental induction of nocardiosis in yellowtail, Seriola quinqueradiata Temminck and Schlegel by artificial challenge

Challenge methods for inducing nocardiosis, caused by Nocardia seriolae in yellowtail, Seriola quinqueradiata, were evaluated. The first method involved intraperitoneal injection of 1.1 x 10(2), x 10(3) and x 10(4) cfu of N. seriolae; the second was by bath immersion with three different concentrations of bacterial suspension for 10 min; the third was by intradermal injection using a multipuncture device; the fourth was by oral administration using a tube; the fifth was based on the co-habitation of uninfected fish with others that had been artificially infected, i.e. intraperitoneally or by immersion for 10 min. The LD(50) values for the infection trials were 1.9 x 10(2) (intraperitoneal injection), 1.5 x 10(4) mL(-1) (immersion), 4.3 x 10(6) (intradermal injection) and 1.7 x 10(7) (oral administration). In the co-habitation challenge, mortalities were 70% and 50% in groups of non-infected fish mixed with fish infected by the i.p. injection and immersion methods, respectively. Fish challenged by intraperitoneal injection developed adhesions. Fish challenged by other methods did not show any gross clinical signs and moribund fish were similar to natural infection.     

Changes in Volatile Compounds of Dark and Ordinary Muscles of Yellowtail (Seriola quinqueradiata) During Short-Term Cold Storage

ABSTRACT

Changes in volatile compounds in dark and ordinary muscle of yellowtail during 2 days of refrigerated storage at 5°C were investigated. Twenty-seven compounds were identified in ordinary muscle and 39 in dark muscle during 2 days of storage at 5°C. Thirteen compounds at Day 0 of storage and 29 compounds at Day 2—such as 2,3-pentadione, 1-penten-3-ol, (Z)-2-penten-1-ol, and (E,Z)-2,4-heptadienal—identified in the dark muscle showed significantly higher values compared to ordinary muscle. Levels of thiobarbituric acid-reactive substances (TBARS) in dark muscle were significantly higher than those in ordinary muscle throughout 2 days of storage period, and a significant increase in TBARS occurred in just dark muscle at Day 2 of storage. In ordinary muscle, viable cells remained at the same order of magnitude as their initial values for 2 days. Eight aldehydes in ordinary muscle and 25 volatile compounds in dark muscle increased significantly without microbial action prior to increase in TBARS during short-term cold storage. Principal component analysis of the volatile compounds in dark and ordinary muscle was able to differentiate between different storage time samples of same muscle type as well as different muscle samples of same storage time.     

Effects of dietary phosphorus level on non-faecal phosphorus excretion from yellowtail (Seriola quinqueradiata Temminck & Schlegel) fed purified and practical diets

Non-faecal phosphorus (P) was determined for large yellowtail to estimate a minimum available P requirement (Experiment  1) and to justify inorganic P supplementation in a fish meal-based diet (Experiment 2). In Experiment 1, purified diets with incremental P concentrations were fed to yellowtail (mean weight 917 g) at a feeding rate of 1.5% of body weight. The peaks of non-faecal P excretion appeared 5–6 h after feeding in fish fed more than 4.5 g available P kg⁻¹ dry diet. Broken-line analysis indicated that the minimum available P requirement was 4.4 g kg⁻¹ dry diet. In Experiment 2, a purified diet (PR) containing 6.5 g available P kg⁻¹ and a fish meal-based diet with (F1) and without (F0) additional phosphorus were fed to yellowtail (mean weight 1.1 kg) at 1.5% (PR) and 2% (F0 and F1) feeding rates respectively. There was no significant difference in P excretion between fish fed the F0 (5.5 g soluble P kg⁻¹ dry diet) and the PR diet. However, significantly higher (34.5%) amounts of non-faecal P excretions (7.4 g soluble P kg⁻¹ dry diet) were found in fish fed F1 compared with the F0 diet. This suggested that there was an excess of dietary P in the F1 diet and that supplementation is not needed in fish meal-based diets for large yellowtail.     

The abundance of juvenile yellowtail (Seriola quinqueradiata) near the Kuroshio: the roles of drifting seaweed and regional hydrography

We assess the effect of drifting seaweed (Sargassum sp.) biomass, geography and hydrography on juvenile yellowtail (Seriola quinqueradiata) abundance variation off the southeast coast of Japan, near the Kuroshio Current. The amount of drifting seaweed mats progressively increased northeastward into the cooler, coastal waters. Frontal structure indexed using a station‐to‐station ΔSST did not explain spatial variation in the seaweed mat distribution, although the western extent of the Kuroshio Current appeared to act as a boundary. Juvenile yellowtail constituted 51–62% of the fish collected in association with drifting seaweed mats in April 1996 and 1997 and 29% in June 1996. The abundance of juvenile yellowtail was positively correlated with seaweed biomass. The geographic distribution of juvenile yellowtail associated with drifting mats varied among sampling periods, being more southwesterly in April and more northeasterly in June. Simple multiple regression models based on seaweed biomass and geographic distribution (latitude) explained between 35% and 43% of the variation in juvenile yellowtail abundance in spring. Associations with spatial and temporal variations in hydrographic conditions did not contribute to explained variation in a meaningful manner. The results presented here indicate that, off the southeast coast of Japan during April, yellowtail juveniles are likely to be most abundant when seaweed biomass is high, occur offshore, and are bounded by the western extent of the Kuroshio Current near the 19–20°C SST isotherm.     

Effect of reward level on the number of food demands in yellowtail Seriola quinqueradiata

ABSTRACT: The effect of reward level (amount of food received in response to one trigger actuation) on the self-feeding activity of juvenile yellowtails was examined. Three groups of 10 juvenile yellowtails (mean bodyweight, 65.6 g) were allocated randomly to three 200 L cylindrical tanks set in the experiment room. Each tank was illuminated by overhead fluorescent lamps with a light : dark photoperiod regimen of 12 h : 12 h (light 06.00–18.00 hours). A rod-type tactile switch was used to activate the self-feeding device. Three levels of reward were set up by installing a different number of identical feeders for each group: one feeder for the low-reward group, three feeders for the medium-reward group and five feeders for the high-reward group. Each feeder delivered 3–7 pellets per actuation. Yellowtails in all groups showed a clearly diurnal feeding pattern that was synchronized to the given photoperiod. Average number of feeder actuations per day was highest (219/day) in the low-reward group. Second highest was the medium-reward group (116/day), and last was the high-reward group (67/day). The resultant average feed intake per day was 27.1 g/day in the low-reward group, 31.5 g/day in the medium-reward group and 28.4 g/day in the high-reward group. Thus, yellowtails appear to have the ability to regulate the amount of feed delivered daily by increasing the number of food demands when the reward is low and decreasing the number of food demands when the reward is high.     

Hemolytic suppression roles of taurine in yellowtail Seriola quinqueradiata fed non-fishmeal diet based on soybean protein

ABSTRACT:   To elucidate the hemolytic suppression roles of taurine and the necessity of dietary taurine supplementation in yellowtail Seriola quinqueradiata fed a diet without fishmeal, juvenile fish with an initial body weight of 250 g were fed for 40 weeks in floating net cages on soybean protein diets supplemented with 0, 3.0, 4.5 and 6.0% taurine. Taurine concentration of the experimental diets were 0.03, 33.9, 52.8 and 71.6 mg/g, respectively. On the 21st week, fish fed the taurine unsupplemented diet had inferior growth and feed performances, higher death, and there were incidences of green liver and hemolytic anemia. In this group, hepatic and plasma taurine concentrations, serum osmolality and osmotic tolerance of erythrocytes (EC50 value) were significantly lower, and plasma hydroperoxide concentration was markedly higher than in the taurine supplemented groups. These conditions markedly improved corresponding with the increase of dietary taurine concentration. These results indicate that taurine plays a role in hemolytic suppression through osmoregulation and biomembrane stabilization in fish. In addition, it is suggested that yellowtail requires dietary taurine as an essential nutrition for maintaining physiological condition normally.     

Effects of taurine levels in broodstock diet on reproductive performance of yellowtail Seriola quinqueradiata

The effect of dietary taurine was investigated on reproductive performance in yellowtail Seriola quinqueradiata. Two-year-old fish of average body weight 6.1kg were fed on diets containing three levels of taurine (T-0, T-0.5 or T-1.0%) for 5 months prior to spawning. For spawning investigations, fish were induced to maturity by human chorionic gonadotrop in injection (600 IU/kg-fish) and artificially inseminated. Oocyte growth improved significantly (P<0.05) with the increase of dietary taurine. The collection of eggs from females reared on the T-0% diet was not successful. The success rate of spawning for females fed on T-0.5 and 1.0% diets was one out of six, and six out of seven, respectively. The taurine levels of the liver and serum in the T-0% diet group were much lower than that in the T-0.5 and T-1.0% diet groups (P<0.05). Fish fed the T-0% diet showed higher contents of serine in the liver and serum. The taurine content of the ovary was not significantly different among the different dietary treatments. These results indicate that taurine has a positive effect on the improvement of spawning performance of yellowtail.     

Effects of dietary supplementation with feeding stimulants on yellowtail Seriola quinqueradiata (Temminck & Schlegel; Carangidae) protein digestion at low water temperatures

Feeding trials were carried out to examine substances that could be used as supplements in low‐protein/high‐lipid diets to improve protein digestion of yellowtails (Seriola quinqueradiata) during winter. Dietary supplementation with synthetic or natural (krill and squid extracts) feeding stimulants (FS) improved feed intake and growth performance of yellowtails. Moreover, the apparent protein digestibility (APD) and pepsin, trypsin and chymotrypsin secretions in fish fed diets supplemented with the different FS were superior to those in fish fed the control diet. These findings suggest that the dietary inclusion of either synthetic or natural FS is a potential tool for improving protein digestion at low water temperatures, and may provide a promising solution for the winter growth retardation experienced in yellowtail culture.     

Molecular diagnosis of Myxobolus spirosulcatus associated with encephalomyelitis of cultured yellowtail, Seriola quinqueradiata Temminck & Schlegel

Mass mortality of cultured yellowtail, Seriola quinqueradiata, has recently been reported from fish farms in western Japan. Previous studies revealed that diseased fish were characterized by encephalomyelitis and presporogonic stages of a myxosporean‐like parasite in the spinal cord. However, the parasite has remained unidentified because of the lack of mature stages being present. Thus, in the present study, analysis of the small subunit ribosomal DNA (18S rDNA) of the parasite as well as in situ hybridization (ISH) studies using histological sections of the infected tissue was conducted. The 18S rDNA of the myxosporean had higher sequence similarities with those of bile‐duct‐infecting myxosporeans rather than those infecting nervous tissues and was identified as Myxobolus spirosulcatus. The ISH using specific probes demonstrated that the DNA amplified was derived from the multinuclear organisms found in histological sections. A highly sensitive and specific PCR‐based assay for M. spirosulcatus was developed, which revealed a high prevalence of infection in cultured yellowtail that exhibited the clinical signs of encephalomyelitis.     

Lipid composition and deposition of cultured yellowtail Seriola quinqueradiata muscle at different anatomical locations in relation to meat texture

ABSTRACT:   The present study was undertaken to assess the lipid composition and deposition in muscle at three anatomical locations in cultured yellowtail and to investigate the effect of lipid composition and deposition on meat texture. Lipid deposition in muscle was studied by histochemical staining of lipid with Sudan dye. Lipid class composition analysis showed that neutral lipids were the main constituents of lipid in cultured yellowtail and accounted primarily for the variation in muscle lipid content with the anatomical location of meat, as well as with season, whereas the polar lipid content remained almost constant. Furthermore, muscle neutral lipid content was correlated negatively with meat breaking strength; however, no correlation was observed between muscle polar lipid content and meat breaking strength. The histochemical study revealed that, in yellowtail muscle, lipid is preferentially deposited in the myosepta and, with increases in muscle lipid content, additional fat is deposited along sparsely distributed thin connective tissue. It was also observed that the greater the lipid deposition in collageneous connective tissue, the lower the meat breaking strength; presumably, higher lipid deposition in the connective tissue resulted in weakening of the muscle structure.     

Effects of dietary lipid and phosphorus levels on nitrogen and phosphorus excretion in young yellowtail Seriola quinqueradiata: A preliminary observation

ABSTRACT:   A feeding trial was conducted to investigate the effect of dietary lipid and phosphorus levels on nitrogen and phosphorus excretion of young yellowtail under on-site conditions for 4 months. Three levels of dietary lipid (200, 250 and 300 g/kg) and four levels of supplemental phosphorus (0, 2, 4 and 7 g/kg) were tested in a complete randomized design with a 3 × 4 factorial arrangement. Each net cage of 170 yellowtail were fed the experimental diets for 4 months and the fish grew from approximately 346–912 g, at water temperatures between 18 and 23°C. Dietary phosphorus levels did not cause any difference in weight gain, specific growth rate, feed conversion ratio and nitrogen retention. However, its increasing supplemental levels reduced phosphorus retention, consequently increasing its excretion, whereas nitrogen excretion remained uninfluenced. In contrast, increasing the dietary lipid level resulted in its greater deposition in the whole body of young fish leading to a reduction in nitrogen excretion. This study has shown that phosphorus levels need not necessarily be high in the diets of young yellowtail. In addition, dietary lipid can be manipulated favorably to produce environmentally suitable diets.     

Seasonal changes in proteolytic enzymes of yellowtail Seriola quinqueradiata (Temminck & Schlegel; Carangidae) fed extruded diets containing different protein and energy levels

Seasonal variations in pepsin, trypsin and chymotrypsin activities and protein digestibility were studied in yellowtails (Seriola quinqueradiata) reared for 1 year with extruded diets containing different levels of protein. Trypsin and chymotrypsin storage levels in the digestive tissues of starved fish were affected by seasonal changes in water temperature. Actual digestion activities of trypsin and chymotrypsin were low at lower water temperatures, but pepsin activity in the stomach tissue was not affected by low temperatures. On the other hand, trypsin and chymotrypsin activities in the intestinal contents were higher during lower water temperature months, while pepsin activity in the stomach contents was low at lower water temperatures. Apparent protein digestibility (APD) did not differ among the dietary treatments in the higher water temperature months, while in colder months it was higher in fish fed diet 1 than in fish fed diets 2 and 3. The APD values reflected pepsin activity in the stomach contents in all sampling months. Therefore, lower APD in colder months seems to be attributed to lower protease activity in the gastric digesta, implying that enhanced pepsin secretion from the stomach tissue might improve protein digestibility and growth performance in yellowtails during winter.     

Partial replacement of fish meal with plant protein sources using organic acids to practical diets for juvenile yellowtail,Seriola quinqueradiata

An experiment was conducted to investigate the effects of phosphorus (P), citric acid (CA) and formic acid (FA) supplementation on growth and loading of nitrogen (N) and phosphorus (P) in juvenile yellowtail fed fish meal (FM) and alternate plant protein (APP) diets. Six diets designated as F49 (490 g kg^?1 FM‐based), F49 + P (490 g kg^?1 FM with 5 g kg^?1 inorganic P), F31 + CA (310 g kg^?1 FM containing 200 g kg^?1 APP with 5 g kg^?1 CA), F31 + FA (310 g kg^?1 FM having 200 g kg^?1 APP with 4 g kg^?1 FA), F23 + CA (230 g kg^?1 FM containing 300 g kg^?1 APP with 5 g kg^?1 CA) and F23 + FA (230 g kg^?1 FM having 300 g kg^?1 APP with 4 g kg^?1 FA) were formulated. Yellowtails were fed one of the diets for 12 weeks under on‐site conditions at water temperature 22.0–27.0 °C. F49 + P gave the best growth, while F23 + CA the lowest. Specific growth rate and feed conversion ratio of F31 + CA were similar with control group. Addition of CA to APP diets significantly increased retention of P; hence, its excretion was lowered. The results of this study suggest that FM could be replaced up to 70% with the addition of 5 g kg^?1 CA to a low P‐containing plant protein sources diet without inorganic P supplementation in juvenile yellowtail diets, which in turn would enable a reduction in environmental pollution from aquafeeds.     

The marine temperature and depth preferences of Arctic charr (Salvelinus alpinus) and sea trout (Salmo trutta), as recorded by data storage tags

Eleven Arctic charr (Salvelinus alpinus) (370–512 mm) and eight sea trout (Salmo trutta) (370–585 mm in length) were tagged externally or internally with depth‐ and temperature‐measuring data‐storage tags (DST) before they were released into the sea in the Alta Fjord in north Norway in June 2002. All sea trout were recaptured after they spent 1–40 days at sea, while all Arctic charr were recaptured after 0.5–33 days at sea. On average, trout preferred water about 0.6 m deeper and 1.3°C warmer than Arctic charr. Arctic charr spent >50% of their time between 0 and 1 m depth, while trout spent >50% of their time between 1 and 2 m depth. Both species spent >90% of their time in water no deeper than 3 m from the water surface. However, sea trout dove more frequently and to greater depths (max. 28 m) than Arctic charr (max. 16 m), and these deep dives were most frequently performed at the end of the sea migration. Arctic charr demonstrated a diel diving pattern, staying on average about 0.5 m deeper between 08:00 hours and about 15:00 hours than during the rest of the 24 h, even though there was continuous daylight during the experiments. When comparing data obtained from the DSTs with temperature measurements within the fjord system, the two species were observed to select different feeding areas during their sea migration, the sea trout choosing the inner and warmer parts of the fjord, in contrast to the Arctic charr that preferred the outer, colder parts of the fjord. The observed differences in migration behaviour between the two species are discussed in relation to species preferences for prey and habitat selection, and their optimal temperatures for growth.