QUANTITATIVE OBSERVATIONS ON THE POPULATION ECOLOGY OF BRANCHIURA-SOWERBYI (OLIGOCHAETA, TUBIFICIDAE)

Cohorts of Branchiura sowerbyi were reared at different temperatures and initial population densities in order to obtain data suitable for the interpretation of population dynamics in field populations. Percent hatching from cocoons reaches its maximum at 25-degrees-C and decreases towards lower and higher temperatures. Embryonic development time, T(E), was measured and the relative threshold temperature, 10-degrees-C, calculated by extrapolation. The degree day requirement for embryo development is 195-degrees-C d. The time of first cocoon laying (T(gm)) was observed and the ratio T(E)/T(gm) was seen to fit with that of other tubificid species cultured so far. Embryo mortality is rather high, while worm mortality is low or very low. Fecundity increases from 15 to 20-degrees-C but decreases at 25-degrees-C. A mathematical model for the simulation of population densities with four size-stage compartments is suggested. It could be used for the optimization of worm uptake (simulated as stage specific mortality) in mass cultures reared for the production of Branchiura, to be used as food for fish fingerlings.