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

Cohorts of Branchiura sowerbyi were reared at different temperatures a nd initial population densities in order to obtain data suitable for t he interpretation of population dynamics in field populations. Percent hatching from cocoons reaches its maximum at 25-degrees-C and decreas es 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 o ther tubificid species cultured so far. Embryo mortality is rather hig h, while worm mortality is low or very low. Fecundity increases from 1 5 to 20-degrees-C but decreases at 25-degrees-C. A mathematical model for the simulation of population densities with four size-stage compar tments is suggested. It could be used for the optimization of worm upt ake (simulated as stage specific mortality) in mass cultures reared fo r the production of Branchiura, to be used as food for fish fingerling s.