Alexander Chong

Partial characterization and activities of proteases from the digestive tract of discus fish (Symphysodon aequifasciata)

A series of studies based on biochemical assays and electrophoretical observations was conducted in order to partially characterise various types of proteases present in the digestive tract of discus (Symphysodon aequifasciata), a highly valuable ornamental species. Casein digestion assays revealed the presence of acidic protease from the stomach region with optimum activity at pH 2.0 and alkaline proteases from the intestinal section with optimum activities observed at pH ranging from 7.5 to 9.0 and 11.5 to 12.5, respectively. Further assays with specific substrates and also pre-incubation with specific protease inhibitors showed the importance of trypsin and chymotrypsin in protein digestion while also revealing the presence of serine-proteases and metallo-proteases, respectively. SDS-PAGE technique using casein as substrate and specific protease inhibitors also showed the presence of eight distinct proteases based on molecular weights ranging from 19.2 to 76.5 kDa.

Production of Hybrid Red Tilapia, Oreochromis mossambicus × O. niloticus, at Varying Stocking Densities in Portable Canvas Tanks

Abstract The influence of stocking density on the growth, feed utilization and population characteristics of red hybrid tilapia (Oreo-chromis mossambicus×O. niloticus) raised in portable canvas tanks was investigated. Duplicate groups of hybrid red tilapia were stocked into ten canvas tanks each sized 3.05 m ×0.92 m ×1.22 m with a water depth of 0.45 m at a rate of 79, 119, 159, 198 and 328 fish/m3. The fish were maintained on a commercial diet containing 34% crude protein and 4% crude lipid and fed twice daily for 24 weeks. The stocking rate of 79 fish/m3 resulted in the highest specific growth rate (SGR) and relative growth rate (RGR) but was not significantly different from stocking rates of 119 and 159 fish/m3. However, feed conversion ratio (FCR), condition factor (CF), and survival did not differ significantly (P> 0.05) among all stocking densities. Based on these findings, a maximum stocking rate of 159 fish/m3 is recommended for culture of tilapia with this raceway system.

Cytochrome P450 induction properties of food and herbal-derived compounds using a novel multiplex RT-qPCR in vitro assay, a drug-food interaction prediction tool.

A multiplex RT-qPCR was developed to examine CYP1A2, CYP2D6, and CYP3A4 induction properties of compounds from food and herbal sources. The induction of drug metabolizing enzymes is an important pharmacokinetic interaction with unique features in comparison with inhibition of metabolizing enzymes. Cytochrome induction can lead to serious drug–drug or drug–food interactions, especially if the coadministered drug plasma level is critical as it can reduce therapeutic effects and cause complications. Using this optimized multiplex RT-qPCR, cytochrome induction properties of andrographolide, curcumin, lycopene, bergamottin, and resveratrol were determined. Andrographolide, curcumin, and lycopene produced no significant induction effects on CYP1A2, CYP2D6, and CYP3A4. However, bergamottin appeared to be a significant in vitro CYP1A2 inducer starting from 5 to 50 μmol/L with induction ranging from 60 to 100-fold changes. On the other hand, resveratrol is a weak in vitro CYP1A2 inducer. Examining the cytochrome induction properties of food and herbal compounds help complement CYP inhibition studies and provide labeling and safety caution for such products.

Amino Acid Profile of Various Body Tissues and Eggs of Discus Fish, Symphysodon aequifasciata

Abstract Amino acid profiles of various body tissues from juvenile and adult discus fish, Symphysodon aequifasciata, were compared. Results from whole-body tissue revealed significant difference (P < 0.05) between the levels of lysine, phenylalanine, alanine, aspartic acid, and serine among the two different fish sizes. Levels of arginine, histidine, leucine, methionine, phenylalanine, and threonine were also higher in muscle tissue of adult fishes. Analysis of gill tissues showed significant difference in levels of histidine, isoleucine, lysine, methionine, threonine, tryptophan, aspartic acid, glutamic acid, proline, and serine were significantly different among the different fish stages. This study also showed that among all ten essential amino acids, muscle had the highest levels of histidine, isoleucine, lysine, and tryptophan; gills had the highest level of arginine; while levels of methionine and threonine were higher in the intestinal tissue. Regression analysis between the calculated whole-body A/E ratio of discus juveniles and with quantitative dietary amino acid requirements of several fish species also showed significant correlation, with highest r values (> 0.90) obtained with tilapia, common carp, channel catfish, and Japanese eel. This profile may be useful as a preliminary reference index to evaluate suitability of various ingredients in terms of amino acid profile for development of economical diet for discus farming.

Inhibition of protease activities in discus Symphysodon spp. by three plant meals

Based on biochemical assays and electrophoretical methods, the inhibitory effects of three plant meals (soybean meal, wheat meal, winged bean meal) on digestive alkaline proteases of discus were investigated. Casein assays revealed that increasing levels of soybean meal caused a linear inhibitory effect on activity of protease. SDS-PAGE images revealed that trypsin and chymotrypsin were the inhibited enzymes. Soybean showed the lowest inhibition rate followed by wheat meal and raw winged bean. There was a quadratic relationship between wheat meal levels and its inhibition of protease acitivity. The highest inhibitory effect was obtained with the winged bean meal with inhibition of caseinolytic activities ranging from 3.6–98.6%. Results from this study showed the potential of both soybean meal and wheat meal as ingredients for practical diet for discus, while demonstrating the need for further improvement in processing method for winged bean meal.

Enhancement of Monosex Hybrid Red Tilapia, Oreochromis mossambicus × O. niloticusProduction in Portable Canvas Tanks Through Mixed-Feeding Strategies

Abstract The viability of mixed-feeding schedules utilizing low-and high-protein diets for the production of monosex hybrid red tilapia, Oreochromis mossambicus × O. niloticuswas evaluated. Male red tilapia juveniles (mean initial weight 16.8±0.08 g) stocked at a rate of 159 fish/m3 in canvas tanks (3.05m × 0.92m × 1.22m) were grown under five different feeding schedules for 24 weeks. Two schedules, using low (25%, A) and high (35%, B) dietary protein were designated as control. Three mixed-feeding schedules tested were: the feeding of 1 day of low protein diet followed by 3 days of high-protein diet (1A/3B); 2 days of low-protein diet followed by 3 days of high-protein diet (2A/3B); and 3 days of low-protein diet followed by 3 days of high-protein diet (3A/ 3B). Results showed that growth performance parameters, such as specific growth rate (% SGR), percent gain, and weight gain were significantly higher (P < 0.05) for fish maintained on the feeding schedule of 3A/3B. Similarly, the feed conversion ratio, protein efficiency ratio, and protein retention values were also significantly better for fish grown under this schedule. In terms of production, the 3A/3B feeding schedule also resulted in the highest total yield (kg/m3) and yield above 250 g. The 3A/3B feeding schedule resulted in a 10.1% protein saving relative to Diet B. These results suggest that a 3A/3B feeding schedule be adopted for the best biological and economical performance of red tilapia.