Serum TransferrinsTransferrins represent a major protein fraction in the serum of tilapias
(4 to 8 mg/ml) and are involved with iron transport for the formation of
hemoglobin. Tilapias exhibit marked polymorphism in their transferrin
patterns (Chen and Tsuyuki 1970; Avtalion et al. 1976). This polymorphism
seems to be controlled by different alleles, the genetics of which have
still to be studied. The reading of transferrin patterns is difficult from 7%
polyacrylamide gel, because their relative mobility (Rm 61 to 72.4%) is the
same as that of the albumins and they are therefore often masked by that
fraction. However, transferrin bands can be easily seen in 6% polyacrylamide
gels, where the albumin spot (Rm 77 to 86%) runs faster than the transferrins
(Rm 65 to 77%). At least 5 distinct transferrin bands in various combinations
were identified in the above-mentioned species. They were numbered as
bands 5 (Rm 78%) to 9 (Rm 64.6%) on the basis of their relative position in
the electropherogram (Avtalion and Wojdani 1971). Plate 1 shows bands
6 to 9.
All the species present a slight intraspecific polymorphism. However,
there are several interspecific differences which permit distinction between
the different species (Avtalion et al. 1976). These interspecific differences
were made more pronounced by eliminating from the parental stocks, indi-
viduals exhibiting overlapping transferrin markers (e.g., transferrin 9 in
S. aureus) (Plate 2). After five years of selection, S. aureus, an endemic
Israeli species, always presents transferrin 8 while the presence of trans-
ferrin 6 is still variable. On the other hand, S. niloticus from different
origins always have the transferrins 7, 8 and 9: up to now it has not been
S. niloticus (Ghana)Plate 1. Electropherogram of S. niloticus (Ghana) in 6% polyacrylamide
gel. Note the hoyogeneity of transferrins (7)-(9). (A) = Albumin; the
figures are % relative mobilities.