A method of preparing a pharmaceutical or cosmetic composition from fish hatching fluid comprising at least the steps of: a) suspending fish eggs in a minimal volume of water; b) inducing synchronized, rapid hatching of said eggs, preferably such that hatching is complete within less than 6 hours for more than 80% of the embryos; c) optionally filtering the hatched eggs to obtain hatching fluid; and d) filtering the hatching fluid using a filter with a pore size of at least 5μm and collecting the filtrate; e) subjecting the filtrate from step (d) to ion exchange chromatography comprising: loading the filtrate on to a DEAE (diethylaminoethyl) ion exchange column; washing the column with a buffered wash solution at a pH of 7-9; eluting leukolectin polypeptides from the column using a first elution buffer comprising the buffered wash solution further comprising a salt at a concentration of 50-100mM; eluting the remaining polypeptides from the column using a second elution buffer comprising the buffered wash solution comprising a salt at a concentration of 500mM to 2M; collecting the eluate from step; f) exchanging the water in the eluate from step with a pharmaceutically or cosmetically acceptable buffer by performing diafiltration using a filter with an exclusion size of less than 12 kDa; g) filtering the solution obtained from step (f) using a filter with a pore size of 0.15-0.30μm and collecting the filtrate; and h) preparing said pharmaceutical or cosmetic composition from the filtrate from step (g). a) suspending fish eggs in a minimal volume of water; b) inducing synchronized, rapid hatching of said eggs, preferably such that hatching is complete within less than 6 hours for more than 80% of the embryos; c) optionally filtering the hatched eggs to obtain hatching fluid; and d) filtering the hatching fluid using a filter with a pore size of at least 5μm and collecting the filtrate; e) subjecting the filtrate from step (d) to ion exchange chromatography comprising: loading the filtrate on to a DEAE (diethylaminoethyl) ion exchange column; washing the column with a buffered wash solution at a pH of 7-9; eluting leukolectin polypeptides from the column using a first elution buffer comprising the buffered wash solution further comprising a salt at a concentration of 50-100mM; eluting the remaining polypeptides from the column using a second elution buffer comprising the buffered wash solution comprising a salt at a concentration of 500mM to 2M; collecting the eluate from step; loading the filtrate on to a DEAE (diethylaminoethyl) ion exchange column; washing the column with a buffered wash solution at a pH of 7-9; eluting leukolectin polypeptides from the column using a first elution buffer comprising the buffered wash solution further comprising a salt at a concentration of 50-100mM; eluting the remaining polypeptides from the column using a second elution buffer comprising the buffered wash solution comprising a salt at a concentration of 500mM to 2M; collecting the eluate from step; f) exchanging the water in the eluate from step with a pharmaceutically or cosmetically acceptable buffer by performing diafiltration using a filter with an exclusion size of less than 12 kDa; g) filtering the solution obtained from step (f) using a filter with a pore size of 0.15-0.30μm and collecting the filtrate; and h) preparing said pharmaceutical or cosmetic composition from the filtrate from step (g).