Changes in biomass and lipid biochemistry during egg development were studied in the tropical shrimps, Alpheus saxidomus and Palaemonetes schmitti, from Pacific Costa Rica. Freshly-laid eggs of P. schmitti were substantially smaller than those of A. saxidomus; dry mass decreased during embryogenesis in the former species but remained almost constant in the latter one. Water content of eggs close to hatching were similar among both species (roughly 75%). Newly-produced eggs of the two species contained ~20% fatty acids per egg dry mass; a comparison with data concerning decapods inhabiting tropical and temperate waters revealed that eggs produced by shrimps inhabiting tropical waters tend to have a higher lipid egg content per dry mass than those from temperate regions. Major lipid classes in the eggs of both species were phospholipids and triacylglycerols which increased and decreased during the incubation period, respectively. The predominant fatty acids of P. schmitti eggs were 16:0, 20:5(n-3) and 22:6(n-3) whereas eggs of A. saxidomus showed high amounts of 16:0, 20:5(n-3) and 16:1(n-7), and remarkably low values of 22:6(n-3) fatty acid. Lipid utilization was more pronounced in P. schmitti; in A. saxidomus, eggs close to hatching still contained 70% of the initially deposited fatty acid content which may indicate an enhanced independence of the newly-hatched larvae on external energy resources. The observed differences may partially be related to different habitat preferences, however, the role of adaptation and phylogeny as determinants of egg lipid biochemistry in caridean shrimps remains to be clarified. Copyright (C) 1998 Elsevier Science Inc.