Human growth hormone like peptides were present in Penaeus indicus as two molecular forms: one with a molecular weight about 25 kDa which is similar to that of the vertebrate growth hormone and a smaller form of 2 kDa. Quantitative variations of hGH-like peptides in different larval stages of three species of Penaeids (Penaeus vannamei, P. stylirostris, P. indicus) suggest a possible involvement of hGH-like peptides in the development. Human growth hormone (hGH) supplementation in the diet of Penaeus vannamei larvae seems to have a positive effect on the size and on the quality of the animals estimated by their resistance to salinity stress.