The extraction procedure was essentially as described by Grossman and Bergman (1992), with slight modifications.
The fish skins were thoroughly rinsed in excess water to remove superfluous material.
They were then soaked in 0.2% (w/v) sodium hydroxide solution for 40 min.
This was followed by soaking in 0.2% sulphuric acid and 1.0% citric acid.
Rinsing with distilled water was carried out between soakings. The final extraction was carried out in distilled water at 45 _C for 12 h.
The extract was then filtered through Whatman filter paper (No. 4), collected and freeze-dried.