Giant freshwater prawn ("Macrobrachium rosenbergii" De Man) embryos can be cultured "in vitro" to hatching in 15% (v/v) artificial seawater (ASW). This technique can be applied as a bioassay for testing toxicity or for the effects of various substances on embryo development and can be used as a simple and low-cost model for studying embryo development. The technique has been implemented for undergraduate biology laboratory investigations in a developmental biology course at Mahidol University, Thailand. To study the effects of salinity and age of embryo at culture initiation on embryo development, survival and hatching, embryos at 3.5 days and 6.5 days old were cultured in 0%, 15%, 30%, and 45% (v/v) of ASW. Embryos survived and developed normally in 15% or 30% ASW but not in 0% or 45% ASW. Likewise, hatching occurred normally at 18.5-19.5 days old in 15% or 30% ASW. Embryos introduced to culture at 3.5 days old were more sensitive to salinity than those started at 6.5 days old. Students in the class showed enthusiasm in laboratory activities, increased interest in developmental biology and positive attitudes towards further study. (Contains 3 figures and 1 table.)