1. A method for improving the cosmetic condition of a mammalian skin, wherein the mammal is administered: (i) a polypeptide containing the amino acid sequence shown in any of the sequences of SEQ ID No.1-4, or a sequence that is at least 90% identical to the sequence, or part of any of these sequences; or (ii) a cosmetic composition comprising (i) and one or more pharmaceutically acceptable excipients and / or diluents. 2. The method according to claim 1, wherein the polypeptide or composition is obtained, or the polypeptide or composition can be obtained by a method comprising at least the following steps: a) suspending fish eggs, preferably salmon caviar, in a minimum volume of water; b) initiating a synchronized, quick hatch caviar, preferably so that more than 95% of the embryos are hatching completed in less than 2 hours; c) filtering the caviar mass after hatching to obtain a medium obtained after hatching; and d) filtering the medium obtained after hatching to obtain a polypeptide and / or composition, the step of filtering the medium obtained after hatching includes at least the following steps: (i) filtering the medium obtained after hatching with a filter, pore size which is at least 5 μm, and collecting the filtrate; (ii) filtering the filtrate obtained in step (i) with a filter whose pore size is from 0.30 to 0.60 μm and collecting the filtrate; (iii) replacing the water in the filtrate obtained in step (ii), pharmaceutical acceptable buffer; (iv) filtering the solution obtained in step (iii) with a filter, and�1. Способ улучшения косметического состояния кожи млекопитающего согласно которому млекопитающему вводят:(i) полипептид, содержащий последовательность аминокислот, приведенную в любой из последовательностей SEQ ID No.1-4, или последовательность, которая по меньшей мере на 90% идентична упомянутой последовательности, или часть любой из упомянутых последовательностей; или(ii) косметическую композицию, содержащую (i) и один или несколько фармацевтиче