Population analysis in mass cultures of Tubifex tubifex

Abstract

Mass cultures of Tubifex tubijkx from Lake Orta were kept in the lab at 20 'C starting with different initial densities (10, 45, 86, 161 ind *jar-'), with the aim of evaluating the effect of density on population numbers and on population parameters. The results show that density mainly controls fecundity, growth, maturation and ovigeration rates. Growth rates and mean number of eggs laid/ovigerous (R,) are inversely related to density, but generation time appears to be directly related. Very low or very high initial densities display, at different times of the culture history, efficient density controls. Intermediate N, seem to bring about situations of bad control, easily leading to numerical overshoots. A possible implementation of a population dynamics model (Bonomi & Di Cola, 1980), originally used for laboratory observations on T. tubifex cohorts was considered, including some density control functions derived from our observations on cohort and mass cultures in some transfer rates and in fecundity rate.

Some characteristics of genetic variants of Tubifex tubifex (M�ller, 1774) (Oligochaeta: Tubificidae) in laboratory cultures

“…Type B genotypes reached the highest weights and produced one cocoon per individual during a two week period whereas Type A needed 10 weeks. Hence, Type B produced a mean of 0.42 eggs per day and reached similar values of egg production as were described by Bonacina et al (1989), 0.33-0.51 eggs per day, 20 "C, but lower than that of Kosiorek (1974), 0.61 eggs/day, 24 "C, Wisniewski (1979), 0.4-0.9 eggs/day in the field, 5 ' C, and Finogenova 8c Lobasheva (1987), 2 eggs/day. Due to its higher weight and greater production of eggs one may assume that Type B is more efficient than Type A in gaining energy from the food.…”

“…Unfortunately, from the fresh weight data it is not clear that the genotypes have different growth rates. Reynoldson (1987) and Bonacina et al (1989) showed that worms reaching higher weights had a higher growth rate and that larger worms also produced more eggs. These results coincide with my data on production of cocoons and fresh weights which show that these differences are genotype dependent.…”

“…Laboratory cultures studied by various research groups indicate that growth rate and time until reproduction can vary over a wide range (Bonacina et al, 1987(Bonacina et al, , 1989Paoletti, 1989;Poddubnaya, 1980;Timm, 1974cited in Poddubnaya, 1980. Data obtained from field observations showed different peaks of abundance in eutrophic as well as in oligotrophic freshwater habitats (Milbrink, 1973(Milbrink, , 1978(Milbrink, , 1983Reynoldson, 1983;Saether, 1980;Sarkka & Aho, 1980;Sarkka, 1987).…”