Dudley D. Culley

Daily variations in the effects of disturbance on growth, fattening, and metamorphosis in the bullfrog (Rana catesbeiana) tadpole

Bullfrog tadpoles subjected to the daily disturbance of water replacement demonstrated differences in the rates of growth and metamorphosis and in fatbody weights which depended on the time of day when water replacement occurred. Early daily disturbances stimulated larval growth whereas midday disturbances stimulated metamorphosis. The time when the daily disturbances caused fattening changed during metamorphosis so that younger tadpoles fattened when disturbed early in the photoperiod and older tadpoles fattened when disturbed at midday.

Effects of Age and Photoperiod on Ovary Size and Condition in Bullfrogs (Rana catesbeiana Shaw) (Amphibia, Anura, Ranidae)

Female bullfrogs (Rana catesbeiana) were reared on one of three light cycles (LD 14:10; 12:12; 8:16; 250C) for either 6, 8, or 12 months, postmetamorphosis. Wild female bullfrogs were caught in September and maintained on LD 4:20, 12:12 and 20:4 (25 C) for 28 days. The photoperiod cycle of LD 12:12 appeared to prevent regression and atresia in either laboratory-reared or wild-caught bullfrogs and is most conducive to maintenance of normal gonadal condition in females under long-term laboratory conditions.

Solar energy conversion efficiency and growth aspects of the duckweed, Spirodela punctata (G. F. W. Mey.) Thompson

Abstract Duckweed, Spirodela punctata (G.F.W. Mey) Thompson, was grown on cattle manure dilutions in small outdoor tanks, under different environmental conditions, during the autumn of 1979 and the spring of 1980. Daily growth rates and solar energy conversion (photosynthetic) efficiencies of duckweed were similar for plants grown on manure dilutions of 2.5, 5.0 and 10.0 gl −1 . There were no significant differences in the daily growth rate or efficiency of photosynthesis for growth periods of 1–4 days. The maximum mean growth rate and solar energy conversion efficiency observed were 12.7 g m −2 day −1 and 4.2% of the photosynthetically active radiation (PAR). The highest values obtained for a single sample were 19 g m −2 day −1 and 4.9%. In terms of dry organic matter production, duckweed was observed to grow as much, or more, during the night as during the day. The source of energy for night growth was not determined. Percent moisture of the duckweed was less at high air temperatures than at low temperatures. Insolation was not significantly related to percent moisture. Percent ash remained relatively constant for all levels of temperature and insolation.

Retention of Intermolt Crawfish in a Hydraulic Soft-Shell Crawfish Separation Unit

Physcial configuration and operational parameters of a prototype hydraulic soft-shell crawfish separator tray are described. The tray takes adavantage of the inability of soft-shell crawfish to resist a continuous water velocity to effectuate their rapid separation from a mixed population of pre-molts and intermolts. Removal of molted crawfish is rapid, and research therefore has focused on retaining intermolts in the separation tray. Given a well desigend separation tray, intermolt loss rates were found to be prinipally controlled by flow rate and intermolt retention time. Electrical inhibition gates powered by twelve-volt alternating current were used to discourage downstream migration of intermolts through administration of a mild shock upon contact. Crawfish became condioned to avoid the tray exit to the extent that they would not voluntarily approach the inhibition gate.