(Decapoda, Astacoidea) by K. Ranga Rao, Carl
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GASTROLITH GROWTH DURING PROECDYSIS IN THE CRAYFISH, FAXONELLA CLYPEATA (HAY, 1899) (DECAPODA, ASTACOIDEA) BY K. RANGA RAO, CARL J. MOHRHERR, DANA REINSCHMIDT and MILTON FINGERMAN Faculty of Biology, Gamma College, University of West Florida, Pensacola, Florida, 32504 and Department of Biology, Tulane University, New Orleans, Louisiana, 70118, U.S.A. INTRODUCTION Several morphological and physiological characters exhibit changes at particular phases of the molt cycle in crustaceans. The crustacean molt cycle has been divided into five major stages and several numbers of substages (Drach, 1939; Drach, 1944; Drach & Tchernigovtzeff, 1967) based on changes noted in the epidermis, exoskeleton and the formation of new setae. The actual number of substages depends upon the particular species being examined. Developing setae can be studied without injuring the animal if transparent parts with setae are located where they can be examined microscopically. If such observations are not feasible, portions of the cuticle have to be sampled at intervals to assess progress during the molt cycle and this generally involves injury to the animals. However, by using criteria such as gastrolith growth (observed by radiography) and the rate of regeneration of lost appendages, attempts have been made to correlate the events with the stages of the molt cycle in crayfishes (Durand, 1960; Travis, 1960a, b; McWhinnie, 1962; Stevenson & Henry, 1971). A comparative analysis of several proecdysial events in the crayfish, Orconectes sinbornil (Faxon, 1884), by Steven- son et al. (1968) revealed a lack of correlation of some proecdysial growth and developmental processes such as gastrolith growth with the proecdysial changes in the exoskeleton. Study of gastrolith growth in relation to the substages of proecdysis is important because those investigators working with large crayfish have relied greatly on the gastrolith indices (obtained by dividing the largest dimension of the gastrolith by the carapace length) in assigning molt stages to the crayfish and correlating physiological and biochemical changes. The gastroliths of crayfishes consist of calcareous concretions which are secreted by the epidermis of the cardiac stomach (Travis, 1960a). Gastrolith deposition is initiated early in proecdysis and these concretions increase in size throughout the course of proecdysis. However, whether the rate of gastrolith growth (as seen in radiographs) can be precisely correlated with the various substages of proecdysis remained to be investigated in detail. Therefore, it was decided to study gastrolith development in crayfish, Faxonella clypeafa ( Hay, 1899 ) , in relation to epidermal changes, biosynthesis of new cuticle, and setogenesis during normal intermolt 257 cycles. In addition, the duration of certain stages of the intermolt cycle was altered by feeding, inanition, and eyestalk ablation and the gastrolith growth in such altered periods was studied also. MATERIALSAND METHODS Immature specimens of Faxonella clypeata were collected from roadside ditches in the area of Pearl River, Louisiana. The stock supply was placed in large plexi- glass tanks while the experimental animals were placed individually in plastic cups containing sufficient water from their natural environment. The animals were fed oatmeal every third day and the water was changed after the crayfish had been allowed to feed for 12 hours. The uropods of the immature crayfish (7 to 11mm carapace length) used in this study were transparent allowing ready observation of epidermal retraction and setogenesis. The method described for use with 4th and 5th stage lobsters (Rao et al., 1973) was employed here. Gastroliths were examined by making radiographs using minimal dosages of soft X-rays (0.416 R/5 seconds) to expose the negatives in a model 805 Faxitron (Field Emission Corp., McMinnville, Oregon). Each animal was prepared for radiography by securing it on its side to a plastic sheet with rubber bands. A nega- tive with a metal number placed upon it was inserted between the animal and the plastic sheet. The resulting radiograms were measured with a calibrated lens inserted within a binocular dissecting microscope. In this study two dimensions of the gastrolith are measured, one is the length while the other is the width. The gastrolith/carapace (G/C) ratio was determined by dividing each of the gastrolith dimensions by the length of the carapace. In order to try to correlate gastrolith growth with the proecdysial substages the animals were staged and X-rayed at frequent intervals (once every 2 or 3 days) during these experiments. Some cray- fish were sacrificed after their stage in the molt cycle and gastrolith size had been determined, portions of their abdominal exoskeleton were fixed in Bouin's fluid for subsequent histological study. Epidermal activity and the deposition of new cuticle were assessed using Mallory's trichrome stain. EXPERIMENTS AND RESULTS - 1. Influence of starvation and feeding on the duration of the cycle. Specimens in the later substages of proecdysis were placed individually in plastic cups and examined daily for the incidence of ecdysis. The day of ecdysis was noted and the animals were then subjected to various feeding regimes and examined continually at frequent intervals through one or two intermolt cycles. It can be seen from fig. 1 that in all the fed animals the durations of the stages A to C and stages D, to D4 were relatively constant whereas the length of the stage Do varied considerably. Stage Do occupied about 50 to 70% of the duration of the intermolt cycle. When the animals were starved after ecdysis they delayed the initiation of proecdysis (fig. 2). Feeding the animals promptly led to the initiation of proecdysis. How- .