THESIS APPROVAL

The study on sexual reproduction of aquatic oligochaetes is not well
established. There are limited to notes on the presence of mature specimens in field
populations. In tubificids and some lumbriculids, breeding may be restricted to brief
periods (Cook, 1968). Fully mature individuals of Peloscolex ferox and Aulodrilus
pluriseta are only present just before breeding commences (Brinkhurst, 1964).
Others, such as Limnodrilus hoffmeisteri and Tubifex tubifex may be found in mature
condition and even breeding at all time in some locality, but even these species often
have periods of intensive breeding (Brinkhurst, 1980). However, these periods may
not be the same from place to another. For example, Limnodrilus hoffmeisteri
exhibited life cycle which varied from site to site and even from year to year at one
site (Kennedy, 1966). Most of aquatic worms became mature and reproduced within
12 months. Aston (1968) found that Branchiura sowerbyi take 1 year breeding cycle
both in field and in the laboratory. In some instance, worms might take as long as 24
months to mature depending on season and localities. Brinkhurst (1964) found the
available evidence that Tubifex costatus, Aulodrilus pluriseta and Peloscolex ferox
take 2 years to mature and breed. Most of these studies suggested that the majority of
breeding worms die after sexual reproduction. However, in some species, particular
on Tubificidae, are known to be capable of surviving as immature worms and
breeding a second time by having developed a new set of reproductive organs
(Brinkhurst and Kennedy, 1965).
2. Habitat and Distribution
Aquatic oligochaetes are widely distributed. Most genera of the Tubificidae
and Naididae are cosmopolitan and several species have been reported from every
continent. In contrast, the Lumbriculidae are more limited in distribution, with over
35 species known only from Asia, nearly 40 in Europe and about 10 in North America
(Brinkhurst and Jamieson, 1971).
Habitat preferences for aquatic oligochaetes can be established with reference
to the physico-chemical parameters of the environment or any other recognizable
ecological criteria. Several species of Peloscolex, Tubifex, Limnodriloides,
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