Biology Reference
In-Depth Information
cholinergic transmission attenuates cognitive impairment in zebrafi sh (Yu
et al., 2006). Koshimizu et al. (2011) describe the possibility of inducing
embryonic senescence and laminopathies in zebrafi sh harboring disturbed
expressions of the
lamin A gene
(
LMNA
). Translational blocking of the
LMNA
induces apoptosis, cell cycle arrest and cranio-facial abnormalities. Hence
the induction of embryonic senescence by cryptic splicing of
LMNA
reduces
the life span from 35-40 months in
zprogerin
transgenic zebrafi sh to 25-35
months in
zpregerin
transgenic
.
Incidentally, studies on the ageing process
covering the entire life span are required to have a better understanding
of reproductive senescence. But “there have been few studies, which have
set out specifi cally to investigate the ageing process throughout the life
span of any fi sh” (Woodhead, 1978). “Little has changed since” (Gerhard,
et al., 2002). Besides there are also wide differences in the life span among
different strains within a species. For example, mean life span of the outbred
zebrafi sh is 42 months with the longest longevity of 66 months. But the
golden sparse
zebrafi sh survives for 56 months with the longest longevity
of 58 months. Resvertol, a natural phytoalexin present in grapes and red
wine is shown to increase longevity of the short-lived fi sh
Notobranchius
furzeri
from about 13 weeks to 18-22 weeks by retarding the expression of
age-related markers of senescence (Valenzano et al., 2006).
The asymmetric mitotic cystic division is the source of oocytes and
Oogonial Stem Cells (OSCs) (Fig. 32). Hence the rate of egg/litter production
by a female fi sh may reveal whether the generation of oocytes and OSCs
is slowed down or ceased, with advancing age or increasing body weight.
This may also serve as a signal for the onset of reproductive senescence. A
voluminous body of literature is available on Fecundity (F) of fi shes. Many of
them show that Batch Fecundity (BF) is related to the volume of body cavity
available to accommodate the ripe ovaries. As fi shes vary enormously in
their body shape, body weight, rather than size and age, is better correlated
with F and BF (see Pandian, 2010). Hundreds of publications describe the
relation of body size with F or BF, but have not provided body weight of
the test fi sh (e.g., Thibault and Schultz, 1978) or their data are limited to
a fraction of the early stage of life span; for instance, the reported data on
body size-fecundity relation in
Poeciliopsis lucida
and
Poecilia reticulata
are
limited to 30-31% of the life span of these poeciliids (Thibault and Schultz,
1978). Rarely, very few authors have provided all or most of the desired
data; analysis of their data confi rms that the fi sh do indeed experience
reproductive senescence.
To estimate the number of broodstock required to regularly supply
the desired number of fry, Coward and Bromage (1999) have maintained
a stock of brooders of
Tilapia zilli
, a substratum (repeat) spawning cichlid
of the size ranging from 32 to 461 g for a period of 80 days. Thankfully,
they have reported data on BF, inter-spawning interval, relative fecundity
