Pergamon Camp. Biochem. Physiol. Vol. zyxwvutsrqponmlkjihgfedcbaZ IOSA. Nos 213, pp. 213-219, 1994 Ekvicr Science Ltd Printed in Great Britain Microdeterrnination of dry mass content in the uterine fluid of four species of viviparous sharks zyxwvutsrqponm (Squalus acanthias, Carcharhinus plumbeus, M ustelus canis and Rhizoprionodon terraenovae) Brian D. Strahl and Julian Lombardi Department of Biology, The University of North Carolina at Greensboro, Greensboro, NC 27412-5001 U.S.A. We describe a micromethod for the determination of dry mass content and wet weight in small ( 2 20 p 1) samples of shark uterine (= periembryonic) fluid using a volumetric micropipette and electrobalance. Periembryonic fluid and maternal blood plasma from pregnant specimens of the viviparous sharks Squalus ac(ulthias, Carcharhinus plumbeus, Mustelus canis and Rhizoprionodon terraenovae were analyzed for dry mass content. Values for dry mass (mg/ml), fluid density (g/ml) and percent dry mass are calculated for the periembryonic fluids and maternal blood plasmas of each species. These results are discussed in relation to the dry mass content of periembryonic fluids in other viviparous sharks. Key words: Viviparity; Shark; Microdetermination; Dry mass content; Uterine fluid; Squalus acanthias; Carcharhinus plumbeus; Mustelus canis; Rhizoprionodon terraenovae. Comp. Biochem. Physiol. 108A, 213-219, 1994. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML Introduction Intracapsular and/or intrauterine fluids which surround the developing embryos of viviparous elasmobranchs have been impli- cated as a source of embryonic nutrition during gestation in species which employ a paraplacental mode of maternal-embryonic nutrient transfer. Previous studies have pro- vided information on the chemical compo- sition of such periembryonic fluids, e.g. total protein concentration (Lombardi et al., 1993), total lipids (Ranzi, 1934; Lom- bardi et al., 1993), total glucose (Lombardi et al., 1993) and amino acid composition Correspondence to: Julian Lombardi, Department of Biology, The University of North Carolina at Greensboro, Greensboro, North Carolina 27412 U.S.A. Fax (919) 334-5839. Received 21 June 1993; accepted 6 August 1993. (Wourms and Bodine, 1983; Files and Lom- bardi, 1993). However, earlier studies have focused on the analysis of only a subset of the total materials that can potentially serve as sources of embryonic nutrition. Pioneer- ing studies by Ranzi (1932,1934) provide a baseline of comparative information on the composition of periembryonic fluids in some viviparous sharks and rays. These early studies include information on percent dry weight, percent water, percent organic and inorganic content in periembryonic fluids of eight species of sharks. There are no modern studies which ad- dress comparative aspects of the dry mass content of periembryonic fluids in viviparous sharks. We present a compara- tive analysis of the total dry mass content of periembryonic fluids and maternal blood 213