Solutions to an alien species invasion from aquarium aquaculture: Isolation and characterization of acid soluble collagen from sailfin catfish, Pterygoplichthys disjuctivus (Weber, 1991) in Sri Lanka

Sailfin catfish (Pterygoplichthys disjunctivus) has become an invasive species within inland water bodies in Sri Lanka but there are no controlling methods presently. Present study investigates the suitability potential of acid soluble collagen/ gelatin from P. disjuctivus, to establish commercial demands for this invasive fish. Samples were collected from Udawalawa Reservoir, Sri Lanka and categorized into two lengths groups according to the length; L1 (30.6 ± 2 cm) and L2 (25.1 ± 3 cm). Acid soluble collagen was extracted from skin, flesh, bone and fin of P. disjuctivus using established acid soluble methods. The average yield of collagen (w/w%) on wet weight basis from skin, flesh, bone and fin for L1 were 26.20 ± 3.32%, 10.66 ± 2.01%, 3.40 ± 0.73%, 3.19 ± 1.79% and for L2 were 22.96 ± 2.16%, 9.19 ± 0.72%, 3.01 ± 0.63%, 2.84 ± 1.06%, respectively. There were significant differences in average yield of collagen among different tissues of fish within the same length group but there were not among the two length groups (p ≥0.05). The moisture content in the collagen extracted from, skin, flesh, bone and fin of L1 were 78.30 ± 0.1% , 84.0 ± 0.1%, 75.18 ± 1.02%,  and 75.45 ± 0.95% and for L2 were 80.07 ± 0.15%, 83.86 ± 1.05%, 78.19 ± 0.95%, 77.12 ± 1.06% respectively; Similarly, protein contents were 48.14 ± 1.05%, 54.43 ± 2.99%, 48.14 ± 0.95%, and 48.56 ± 0.90% for L2  49.29 ± 1.03, 49.13 ± 0.95%,  47.26 ± 0.95% and 47.73 ± 0.95%; lipid content of skin, flesh, bone and fin of L1 were 0.9 ± 0.1%, 0.97 ± 0.06%, 1.08±0.15%, and 0.89±0.09% and for L2 were 0.96 ± 0.03%, and 0.99 ± 0.03%, and 1.20 ± 0.11%, and 1.03 ± 0.06% respectively; and ash content of skin, flesh, bone and fin of L1 were 25.76 ± 0.95%, 22.16±1.11%, 32.16±0.91%, and 29.18±0.95% and for L2 were 34.10 ± 0.95, 22.29 ± 0.95%, 28.166 ± 0.9 and 41.17 ± 1.00% respectively. In collagen extracted, % protein, %lipid and %ash were significantly different among flesh, skin, bone and fin within the same length group (p ≤ 0.05) but not among length groups (p ≥0.05). UV spectrum and FTIR spectrum of extracted four types of collagen indicated high percentage of collagen. Flesh and skin of P. disjuctivus can be recommended as a good source of collagen for potential industrial applications.