Carly&Barrett
Garra rufa is a small warm-freshwater species otherwise known as the 'doctor fish'
which is increasingly popular for pedicure treatments, and as an alternative therapy
for psoriasis, whereby the fish forage on and remove dead cells from human skin. The
guts of the fish (n = 20) had a mean relative length of 5.35 ± 1.11 body lengths,
consistent with other herbivorous cyprinids. An overview of G. rufa digestive
enzymes, including total carbohydrase activity and total proteolytic activity, was
investigated to determine the species’ potential to digest human skin. Proteolytic
activity on skin samples was also investigated directly to test its suitability as a source
of nutrients for G. rufa. Carbohydrases dominated the enzyme profiles, with proteases
less active. Poor nutritional value of skin samples (significantly lower than casein)
suggests that human skin is not an adequate nutritional substrate for G. rufa.
A variety of processing methods were trialled because of the small size of the fish and
of their guts. Fish guts homogenised with their contents showed significantly higher
carbohydrase activity than guts alone. The possibility that gut contents explained this
difference was excluded by testing diet and digesta without enzyme incubation. This
showed glucose activity to be very low (0.76 ± 0.06 mg glucose h-1
). Most previous
studies on fish digestive enzyme profiles have been made on starved fish or those in
which the guts were emptied prior to assay. This raises questions over the validity
and usefulness of these studies, which may have provided misleading data on
maximum enzyme production using the methods described.