Riboflavin Requirement of Fingerling Red Hybrid Tilapia Grown in Seawater

Red hybrid tilapia Oreochromis mossambicus × O. niloticus fingerlings were fed diets containing 0, 2.5, 5.0, 10.0, 20.0 and 40.0 mg/kg, and 0, 2.5, 5.0, 7.5, 10.0 and 20.0 mg/kg of riboflavin in separate 8 and 12 wk feeding studies, respectively. The dietary riboflavin level required to provide maximum growth and survival, and prevent deficiency symptoms in red hybrid tilapia fingerlings was found to be approximately 5 mg/kg of diet. In both trials, fish fed the diet devoid of supplemental riboflavin exhibited anorexia, reduced growth and nervous symptoms after 4–6 wk. Mortality began to occur after the sixth week. None of these abnormalities were observed during the first 6 wk in fish fed the riboflavin supplemented diets. However, by the seventh week, fish fed the diet supplemented with 2.5 mg/kg of riboflavin showed reduced appetite and growth rate. In both experiments, short body dwarfism was observed during week 8 for fish fed the diet without riboflavin supplementation. In experiment 1, fish fed the riboflavin-deficient diet had lens cataracts at week 8. This deficiency sign was not observed in experiment 2. Histological studies of liver, kidney, spleen, lateral muscle, gill and gastrointestinal tract revealed no major histopathological changes.     

Feeding behavior under dark conditions in larvae of sutchi catfish <Emphasis Type="Italic">Pangasianodon hypophthalmus</Emphasis>

Sutchi catfish Pangasianodon hypophthalmus hatch with morphologically immature sensory organs; however, sensory organs develop rapidly with larval growth. Two-day-old larvae commenced ingesting Artemia nauplii. The larvae displayed many taste buds on the barbels, the head surface, and in the buccal cavity. Other sense organs were also well developed at this stage. Feeding experiments revealed that 2-day-old larvae ingested Artemia under both light and dark conditions, moreover, the larvae could ingest frozen dead Artemia. The ingestion rates for 4- and 7-day-old larvae were significantly higher under dark conditions than under light conditions. The rates using frozen dead Artemia were mostly higher than the rates using live Artemia. Therefore, feeding behavior under dark conditions is most likely not mediated by visual or mechanical senses, but rather by chemosensory senses, such as taste buds. Larval fish are vulnerable to predators; thus, if they can search for and eat food at night, they can avoid diurnal predators. The behavior observed here appears to represent their survival strategy. Moreover, these results suggest a new possibility that sutchi catfish larvae can be reared under dark or dim light conditions in order to improve survival and growth rates as in the case of African catfish Clarias gariepinus.     

Influence of Dietary Levels of Magnesium on Growth, Tissue Mineral Content, and Resistance of Channel Catfish Ictalurus punctatus Challenged with Edwardsiella ictaluri

Juvenile channel catfish were fed purified diets supplemented with magnesium (Mg) from Mg sulfate at levels of 0, 200, 400, 600, 800, and 1,000 mg/kg and 0, 200, 400, 600, and 800 mg/kg in two separate feeding studies. In study I, the effect of dietary levels of Mg on growth response, vertebral mineral content, and macrophage chemotaxis were evaluated. Study II had similar objectives except that whole body mineral content was measured, and resistance of channel catfish to Edwardsiella ictaluri challenge was also determined. Fish with an average weight of 10.89 g were stocked at a rate of 50 fish/110‐L aquarium (study I). In study II, fish with an average weight of 4.14 g were stocked at rates of 40 fish/110‐L aquarium. Prior to stocking, each batch of fish was acclimated to laboratory conditions and fed the basal diet for 2 wk. The concentration of Mg in rearing water was 1.8 mg/L. Each diet was fed to fish in quadruplicate and triplicate aquaria to apparent satiation for 10 wk for studies I and II, respectively. Fish fed the basal diet started to die as early as 3 d after the study began (17 d of feeding the diet without Mg supplementation). In both studies, weight gain, survival, and feed efficiency were lowest for fish fed the basal diet but increased with increasing dietary levels of Mg. However, the differences between the values of each of these parameters for fish fed diets containing supplemental Mg were not always significant. Magnesium‐deficiency signs observed were anorexia, sluggishness, convulsions, deformed snout, vertebral curvature, muscle flaccidity, and high mortality. Vertebral and whole body ash concentrations were high, but Mg content was low for fish fed the basal and the 200‐mg Mg diets. Bone Ca content did not differ among fish fed different diets (study I), but whole body Ca tended to increase for fish fed the basal diet, suggesting the possibility of calcification of soft tissues. Macrophage chemotaxis in the presence of exoantigen was highest for fish fed diets supplemented with Mg at 400 and 200 mgkg for studies I and II, respectively. When expressed in terms of chemotaxis index, however, maximum or near maximum value was observed at a dietary Mg level of 400 mg/kg. Thus, a dietary level of Mg of 400 mg/kg from Mg sulfate was required for optimum growth and survival, maintaining high tissue levels of Mg, prevention of muscle flaccidity and skeletal deformity, and stimulating macrophage chemotaxis. Dietary levels of Mg had no effect on the resistance of juvenile channel catfish to Edwarsiella. ictaluri challenge.     

A preliminary study on the protein requirements of Chanos chanos (Forskal) fry in a controlled environment

Milkfish (Chanos chanos) fry with an average weight of 40 mg per fish were stocked in 60-l wooden-glass aquaria filled with 30 l of filtered sea water with a salinity of 32–34 p.p.t. and a temperature of 25–28°C. They were fed diets containing 20, 30, 40, 50 and 60% protein and 2740 kcal of digestible energy per kg at a daily rate of 10% of the biomass for a period of 30 days. Fish which were fed the diet containing 40% protein had the highest weight gain which was significantly higher (P < 0.05) than those of fish receiving the lower dietary levels of protein. Slightly lower weight gains were obtained when fish were fed diets containing 50 and 60% protein. Although feed conversion values were not statistically different (P < 0.05) among all treatments, the value for the 40% protein diet (1.96) was the best. The mean survival rates were low for all treatments but was highest for the 40% protein diet. No significant difference (P < 0.05) was found in the survival rates of fish receiving different treatments. Results show that a dietary level of 40% protein was required by milkfish fry for maximum growth, efficient feed conversion and high survival rate.     

Evanescent-wave biosensor for field serodiagnosis of tortoise mycoplasmosis

Disease has become an increasingly important issue for wildlife management over the past two decades. Adequate surveillance is fundamental for disease prevention and control, thus there is an increasing need for diagnostic assays for wildlife management. The objective of this study was to evaluate the performance of a field-portable biosensor adapted for rapid detection of specific antibodies in tortoise plasma that reflect a history of exposure to Mycoplasma agassizii, which is an agent of tortoise upper respiratory tract disease. Banked plasma samples were tested in two blinded trials, and the parameters that define the reliability of a diagnostic test were estimated based on externally validated tortoise plasma controls. The mean sensitivity of the biosensor (ability to identify exposed tortoises in the group of all exposed individuals) was 78%; the mean specificity (unexposed individuals with negative test result, out of all unexposed individuals tested) was 73%; the mean positive predictive value (exposed individuals with positive test, out of all individuals with positive test) was 82%; the mean negative predictive value (unexposed individuals with negative test, out of all individuals with negative test) was 68%. In a 15-min field-portable format, the biosensor was able to discriminate between true seropositive (n=34) and true seronegative (n=23) tortoise plasma with overall accuracy of 84%. The goals established for the tortoise population can help managers decide whether potential diagnostic errors should impact management decision-making, and whether the benefits of the field-portable format of the biosensor assay outweigh any potential disadvantages.     

Effects of Processing Parameters on Physical Properties of Corn Starch Extrudates Expanded Using Supercritical CO2 Injection

Corn starch was extruded with a corotating twin-screw extruder (24:1 L/D ratio, 31-mm screw diameter) and supercritical CO₂ was injected as a blowing agent. The effects of barrel temperature (80–90°C), screw speed (150–250 rpm), and water injection (30–54 g/min) on specific mechanical energy (SME) input for the process and the physical properties of extrudates, such as expansion ratio, water absorption (WA), water solubility (WS), breaking stress, and elastic modulus, were examined using a response surface methodology. Barrel temperature had the greatest effect on physical properties of extrudates but not on SME input, whereas screw speed and water injection had significant effects on SME input. Extrudates had a smooth surface, and air cells were uniform and closed, providing low WA and WS. Using superimposed contour plots, optimum barrel temperature, screw speed, and water injection rate, based on maximum expansion ratio and minimum SME input, were 94–96°C, 155–175 rpm, and 36–39 g/min, respectively.     

Transcrytalline structures and crystallization kinetics of Polyarylate/Nylon6 Islands-in-a-Sea conjugate fibers for high performance thermoplastic composite applications

We report the isothermal and non-isothermal crystallization kinetics and associated transcrystalline morphological features of polyarylate(PAR)/nylon6 islands-in-a-sea fibers, where 74 PAR islands serve as reinforcing fibers and nylon6 sea component acts as a semicrystalline matrix in final thermoplastic composites. The temperature-dependent polarized optical microscopic images obtained during a cooling process exhibit that the melt-crystallization is dominated by the interfacial crystallization of nylon6 on the surface of PAR fibers, leading to developing a transcrystalline structure. From the isothermal and non-isothermal melt-crystallization analyses of the islands-in-a sea fiber by using differential scanning calorimetry and the Avrami equation, the overall crystallization rates of the nylon6 sea component in the islands-in-a-sea fiber are found to be highly accelerated by the heterogeneous nucleating effect of the PAR island fibers. In addition, it is revealed that the isothermal and non-isothermal melt-crystallization kinetics of the nylon6 in the islands-in-a-sea fibers consists of two different mechanisms of the primary crystallization owing to the interfacial crystallization and the secondary crystallization due to the bulk crystallization.     

Physical properties of dry-heated octenyl succinylated waxy corn starches and its application in fat-reduced muffin

Waxy corn starch was modified by dry heating (130 °C, 2 h) in the presence of octenyl succinic acid (OSA) at different pHs (4, 6, and 8), and the physicochemical properties of the modified starch were evaluated. The dry-heated octenyl succinylated (DH-OS) starch was also evaluated as a partial fat substitute in a muffin. Dry heating of starch under a more acidic condition resulted in lower degree of polymerization (DP_n) but lower degree of substitution (DS). The pasting viscosity of the DH-OS starch prepared under basic conditions was higher than that of the unheated counterparts, whereas that under acidic conditions was lower. It was because the substitution favored basic conditions, and thermal degradation was accelerated by acids. The gelatinization characteristic was not significantly altered by OSA substitution and dry heating. The muffin containing the DH-OS starch had a higher specific volume and a softer texture than the muffin containing maltodextrin. Among the DH-OS starches tested, the starch prepared under acidic conditions produced muffins that had a greater volume, which was most likely due to its low molecular size. The muffin prepared with DH-OS starch at pH 6 was the softest in texture and had characteristics that were relatively close to the full-fat muffin.