Comparative Transcriptome Analysis During the Seven Developmental Stages of Channel Catfish (Ictalurus punctatus) and Tra Catfish (Pangasianodon hypophthalmus) Provides Novel Insights for Terrestrial Adaptation

Tra catfish (Pangasianodon hypophthalmus), also known as striped catfish, is a facultative air-breather that uses its swim bladder as an air-breathing organ (ABO). A related species in the same order (Siluriformes), channel catfish (Ictalurus punctatus), does not possess an ABO and thus cannot breathe in the air. Tra and channel catfish serve as great comparative models for investigating possible genetic underpinnings of aquatic to land transitions, as well as for understanding genes that are crucial for the development of the swim bladder and the function of air-breathing in tra catfish. In this study, hypoxia challenge and microtomy experiments collectively revealed critical time points for the development of the air-breathing function and swim bladder in tra catfish. Seven developmental stages in tra catfish were selected for RNA-seq analysis based on their transition to a stage that could live at 0 ppm oxygen. More than 587 million sequencing clean reads were generated, and a total of 21,448 unique genes were detected. A comparative genomic analysis between channel catfish and tra catfish revealed 76 genes that were present in tra catfish, but absent from channel catfish. In order to further narrow down the list of these candidate genes, gene expression analysis was performed for these tra catfish-specific genes. Fourteen genes were inferred to be important for air-breathing. Of these, HRG, GRP, and CX3CL1 were identified to be the most likely genes related to air-breathing ability in tra catfish. This study provides a foundational data resource for functional genomic studies in air-breathing function in tra catfish and sheds light on the adaptation of aquatic organisms to the terrestrial environment.

The deterioration of weakly vertical linkages in tra catfish industry in An Giang Province, Vietnam

This study analyzes the vertical linkage effectiveness between fish farmers and processing companies on the mutual beneficial relationship, knowledge transfer, quality standards, embedded services, and payment before the United State (US) Department of Commerce has decided to impose new rates of antidumping taxes on tra (Pangasius) fish fillets imported from Vietnam. After conducting the first survey of 70 fish farmers and five in-depth interviews with directors of processing enterprises, representatives of provincial authority, and experts in the field during March and April of 2012 in An Giang province, Vietnam, we found that the mutual beneficial relationship was the most influent factor to vertical linkage effectiveness. However, after new rates of antidumping duties were imposed, we conducted the second survey of 17 in-depth interviews with 12 fish farmers, four local officers and one expert during April and June of 2013 in An Giang province, and recognized that almost all vertical linkages with processing companies to export to the US market have been deteriorated and dispersed.

Recovery of bone powder from salmon by- product and application in production of Tra catfish cake

In this study, salmon by-products were utilised to produce high ash content (AC) salmon bone powder (SBP) using hydrolytic enzyme and apply in the production of Tra catfish cake. The by- products included 61.9% of moisture, 43.1% of protein, 45.4% of lipid, 10.2% of ash, 3.7% of calcium and 2.3% of phosphorus (on dry weight basis). The AC of SBP achieved the maximal value of 46.9% when hydrolytic enzyme of Alcalase, pH value of 6.5, temperature of 60oC, the Enzyme/Substrate (E/S) ratio of 60 U/g protein and time of 4 hours. The obtained SBP contained 23.1% of calcium, 11.7% of phosphorus and without heavy metals such as cadmium, mercury and lead. The fish cake added with 2% of SBP owned the highest gel strength, folding score and whiteness of 287.4, AA and 65.3, respectively and it was accepted by the test panel. Hence, SBP could be used in the production of Tra catfish cake as a mineral supplement.

Investigation of antioxidant capacity of peptide fractions from the Tra catfish by-product-derived proteolysate using Flavourzyme® 500 mg

In this study, the antioxidant potential of peptide fractions isolated from the Tra catfish (Pangasius hypophthalmus) by-product-derived hydrolysate using ultrafiltration centrifugal devices with 3 distinct molecular-weight cutoffs (MWCOs) of 5KDa, 10KDa, and 30KDa was investigated. Firstly, the chemical composition of the Tra catfish byproducts was analyzed. The result showed that the Tra catfish by-products contained 58.5% moisture, 33.9% crude protein, 50.1% crude lipid and 15.8% ash (on dry weight basis). Secondly, the effects of enzyme content, hydrolysis time on the antioxidant activity of the hydrolysate were studied using DPPH• (2,2-diphenyl-1-picrylhydrazyl) radical scavenging method (DPPH• SM), and FRAP (ferric reducing antioxidant potential) method. Flavourzyme® 500 MG was used for hydrolysis. The result revealed that the antioxidant activity of the proteolysate reached the peak when the hydrolysis time was 3h, enzyme/substrate (E/S) ratio was 25 U/g protein, hydrolysis temperature was 500C, pH was 7, and the degree of hydrolysis (DH) of the hydrolysate reached 37.4%. Next, the proteolysate was further fractionated using MWCOs of 5KDa, 10KDa, and 30KDa and the peptide fractions were investigated for their antioxidant activity. The result showed that the <5KDa fraction showed strongest antioxidant activity with the 50% DPPH• inhibition concentration (IC50) of 3079.34±75.29 μg/mL and FRAP value of 611.28±4.5 μM Trolox equivalent. The second strongest fraction was 5-10KDa with the IC50 and FRAPS value of 4709.3 ± 222.22 μg/mL and 323.62±2.54 μM Trolox equivalent, respectively. The 10-30KDa fraction showed weakest antioxidant capacity with the IC50 of 5847.73 ± 128.68 μg/mL and FRAP value of 291.4±2.65 μM Trolox equivalent. The antioxidant peptides derived from Tra catfish by-products proteolysate have the potential to be used as natural antioxidant ingredients in pharmaceutical and food industry.