Edinburgh Napier University

  It has recently been acknowledged that effluents from sewage treatment plants (STPs)
are one potential source of endocrine disrupting chemicals (EDCs). This diverse
group of chemicals can include environmental oestrogens or exoestrogens, substances
that mimic or antagonise gonadal hormones. These are of particular concern because
they are known to impair the sexual development and reproductive success of
vertebrates, including fish. It is well established that reproductive behaviours are
regulated by endogenous hormone concentrations, yet there has been very little work
conducted on the effects ofthese EDCs on behaviour. The experiments described in
this thesis investigate the reproductive behaviour and morphology of adult male
mosquito fish (Gambusia sp.) which have been exposed in the laboratory to low levels
of oestrogens, an oestrogen mimic and sewage effluent and also exposed under
natural conditions through inhabiting two sewage contaminated rivers in NSW,
Australia. All males were observed for reproductive behavioural characteristics in a
standard observation procedure, and several reproductive characteristics were also
recorded: gonopodium length (GPL), gonadosomatic index (GSI: testis to body
weight ratio), testis area (TA mm3
), body condition index (BCI: using Fulton's
condition factor - body weight x 100 / body length3), and number of
spermatozeugmata, or SPZ (visible sperm packets).
Adult male mosquito fish were exposed to 0.4, 2 and lOng/1 diethylstilbestrol (DES),
20, 100 and 500ngll 17~-oestradiol (E2) and 2, 10 and 50~gll octylphenol (OP) for 8-
10 weeks in the laboratory. These experiments demonstrated significant reductions in
the reproductive behaviour of exposed males compared to controls, but no consistent
treatment effects on the other reproductive characteristics of the fish were found.
Exposure of adult male mosquitofish to 25, 50 and 100% treated sewage effluent for
8-10 weeks in the laboratory yielded variable results in reproductive behaviour. Males
collected from an urban polluted river in 1999 and 2000 exposed to 50% and 100%
sewage effluent demonstrated a significant reduction in approach behaviour but not in
duration in female zone or mate attempt. However, no significant differences in reproductive behaviour were observed in exposed males collected from a 'pristine' river.
No differences in reproductive morphological characteristics were found between
treatment groups.
When wild adult males were sampled 10km downstream of St. Marys sewage treatment
plant (STP) outfall in 1999 and 2000 and observed in the laboratory, they did not show
any differences in the reproductive behaviour or morphology compared to upstream fish.
However, males collected Skm downstream of the same outfall in 2002 were suggestive
of a reduction in reproductive behaviour, compared to upstream males. In addition, they
had significantly reduced GPL, TA and GSI compared with upstream. Similar reductions
were found when wild adult males were sampled from another sewage-contaminated
river in NSW, downstream of Quakers Hill STP in 2000 and 2002. Laboratory
examination of males sampled from a site SOm downstream from this sewage outfall
showed significantly reduced levels of reproductive behaviour over both years compared
to upstream. Males collected in 2002 had significantly reduced BCI, T A and suggested
decrease GSI compared to upstream fish, but this was not apparent in the 2000 sample. There were no significant differences in GPL and SPZ counts in fish between up and
downstream sites of this STP outfall.
The overall pattern of results is consistent with a hypothesis of reproductive endocrine
disruption, potentially impacting populations of fish inhabiting sewage-contaminated
rivers.