Sarkar and Bhavna Upadhyay
College, Agra (India)-282001
most animals the seasonally changing pattern of day length provides
the most accurate year-on-year index of time and many fish use the
increasing and decreasing components of this light cycle to coordinate
development. In order to use light in this way, however, firstly the
light must be perceived, secondly, day length change must in some way
be measured and lastly, this information must be transduced into a
suitable 'message' for integration by the newoendocrine cascade
which initiates and then modulates development. Photoperiod is the
ability of organisms to and use the body length as an anticipatory
cue to time seasonal events in their life histories. Photoperiodism is
especially important in initiating physiological and developmental
processes that are typically irrevocable and that culminate at a
future time or at a distant place; the further away in space or time,
the more likely a seasonal event is initiated by photoperiod. A wide
variety of animals from diverse take use the day length or
photoperiod as an anticipatory cue to make seasonal preparations.
Photoperiod is most useful in predicting environmental conditions in
the future or at distant localities; photoperiod provides a go/ no-go
signal that initiates a usually irrevocable cascade of physiological
and development processes that cuminate in reproduction, dormancy
and migration. Day length provides a highly reliable calendar that
animals can use to anticipate and prepare for seasonal change. Unlike
temperature and rainfall, day length at a given spot on earth is the
same today as it was on this date 10 or 10,000 years ago. In this
review we show that, we show that photoperiod is widespread among
fishes and we have made a comprehensive study of photoperiodism in
through the course of their evolution, have adapted themselves to a
wide range external stimuli that co-ordinate their seasonal breeding
activities and migrations. It is well known among keepers of home
aquaria, for example, that the tropical guppy and swordtail, although
capable of breeding all the year round, show a heightening of
reproductive activity with the increasing daylengths of the
spring (Pyle, 1969).
can be shown experimentally that light can affect the state of the
reproductive organs in many species. Thus, goldfish kept in the dark
for a long time show a degeneration of the gonads. Conversely, fishes
belonging to several different families can be induced to display and
show an acceleration of gametogenesis in response to artificially
increased photoperiods, a technique that is widely employed in
commercial trout fisheries where young fishes are induced to ripen
may months in advance of normal by subjecting them to protracted
photoperiods (Baggerman, 1972).
In the few species that have been studied in detail it
appears that light and heat impose a dual control. This is well
demonstrated by the reproductive cycle of the common European minnow,
Phoxinus phoxinus. This fish breeds in May and June, and immediately
following, there is a re-establishment of gametogenetic activity in
the gonads. The proliferation of new germ cells continues throughout
the autumn then comes to a halt during the winter months. With the
arrival of spring there is a recrudescence of gonadal activity and a
rapid completion of maturation in both males and females. For either
sex to attain full maturity requires a combination of long days with
high temperatures. Thus, the increasing daylength and water
temperature in the spring accelerates the fishes into full breeding
condition (Fenwick, 1970 a).
Photoperiodic regulation is not exclusively confined to
the control of the reproductive rhythms, but can also be influential
in other physiological processes. Many fishes at the time of
migration show changes in the activity of the pituitary, thyroid and
interrenal glands, and changes in metabolism and general activity.
The three-spined stickleback undertakes a prespawning migration from
the sea to fresh water during the spring, and a post-spawning
migration back to salt water during the autumn. By experimentally
exposing the fish to a range salinities throughout the year, B.
Baggerman has demonstrated that at the time the fishes are scheduled
to start their spring migration they show a seasonal change in
preference from salt to fresh water, but in the autumn when they
start the downstream journey, there is a return of preference for
more saline waters. The underlying physiological mechanisms are not
known in detail but are thought to involve the pituitary and thyroid
glands which are in turn affected by photoperiods (Baggerman, 1980).
Experimentally, cyclical changes in salinity preference
from salt to fresh water can be induced in these fishes by
maintaining them under long photoperiods and a constant high
temperature, whereas exposure to short photoperiods under similar
temperature conditions, induces the animals to maintain their initial
salt water preference. Thus the daily photoperiods control the time
at which changes in salinity preference take place (Baggerman, 1972).
The Pacific salmon, Oncorhynchus, is another species
that migrates from the sea into fresh water to spawn. In the Coho (O.
kisutch) and sockeye (O. nerka) the young fry hatch out and remain in
fresh water for a year before migrating seawards. As in the
stickleback this departure is presumably induced by the seasonal
assumption of a migration-disposition, indicated by a change in
salinity preference, and timed by a photoperiodic mechanism
(Bullogh,1939). Knowledge of how photoperiod affects
reproduction in fishes can be put to practical use in at least three
ways. First, manipulation of photoperiod can accelerate, maintain or
delay sexual maturation and spawning of broodstock so that spawning
may occur out of season. Second, manipulation of photoperiod can
also inhibit gonadal recrudescence so that in growning fish somatic
growth can be encouraged without the energy drain required for
reproduction (Lam 1983). In the female, there is a large percentage
of the available energy budged that goes into reproduction (Whittier
and Crews, 1987). Third, photoperiod manipulation can reduce
generational time by reducing time between spawning and allow for
accelerated genetic improvements of fish stocks (Lam, 1983).
Fish like all animals, reproduce to maintain
survival of the species. They must not only reproduce but they must
reproduce when maximum reproductive success is possible (Lam, 1983;
Whittier and Crews, 1987; Munro ,1990). Developmental and
maturational events are dominated and coordinated by seasonal changes
in photoperiod, temperature, rainfall etc. (Sanchez-vazquez et
al., 2000). Photoperiod and temperature are generally considered
the most important factors. Seasonal reproduction is influenced by
biotic factors such as temperatures, water quality and photoperiod and
biotic factors such as food availability, predators and pathogens
being at optimum conditions (Bergman, 1987; Whittier and Crews, 1987;
Hontela and Stacey, 1990; Munro, 1990; Sumpter, 1990). Seasonal
activities often appear linked with the changes in environmental
photoperiod and influence the seasonal activities (Vinod kumar and
Fenwick (1970 a) exposed goldfish Carassius auratus
to various photoperiods at several different times of the year, long
photoperiods stimulated gonadal maturation in Carassius but only
during spring. A long photoperiod warm temperature regime also
promotes sexual maturation in other fishes Carassius auratus
(Kawamura and Otsuka, 1950).
is widespread among teleostean fish and has been studied in at least
nine orders, in various species. Photoperiod may provide the go/no-go
signal for seasonal dormancy as well as in migration, sexual
maturation and associated physiology and behaviour in migratory fish.
Fish with short gonadal maturation cycles usually require
sequentially changing day lengths (Bromage et al., 2001).
et. al. (1994) demonstrated that the presence of photopeiodism
and circannual rhythms in echinoderms indicates that photoperiodism
and its regulation of circannual rhythmicity either appeared early in
deuterostome evolution and were lost in cephalochordates, hag fishes,
lampreys and cartilaginous fish, or evolved separately in echinoderms
and bony vertebrates, where photoperiod provides pivotal go/no-go
signals for the seasonal timing of life history events in teleost
fish. Photoperiod may exert the dominant regulatory role of sexual
cycles in many teleost fishes, day length changes in combination with
various temperatures seem to be important in controlling reproduction
in cyprinid and centraorchid fishes (De Vlaming, 1972a) the long
photoperiods are required for the final stages of gonadal maturation
in Phoxinus (Bullogh, 1939). The long photoperiods with warm
temperature during winter and spring brought about sexual maturity in
female goldfish (Kawamura and Otsuka, 1950).
use the length of day or photoperiod to time their seasonal
development reproduction migration and dormancy (Bradshaw and
Holzapfel, 2007). Seasonal activities often appear linked with the
changes in environmental photoperiod (Vinod kumar, 1986).
would regulate the axis photoreceptors, central nervous system,
hypothalamus pituitary gonadotropin, ovarian estrogen secretion,
oogonial proliferation and endogenous yolk formation. In some
vertebrates photoperiod acts as a chief proximate factor in the
regulation of seasonal reproduction. Photoperiod changes accurately
and reliably around the year, so that animals can use this use for
prediction of seasonal changes and accordingly programme their
gonadal development (Fraile et al., 1989). When
goldfish, Carassius auratus were exposed to various
photoperiods at low temperatures several times in the year it was noticed
that the long photoperiods stimulated gonadal maturation only in Spring,
the effect of photoperiod on gonadal activity of goldfish, Carassius
auratus vary with season (Fenwick, 1970 a).
have powerful endogenous components and daily light dark cycles
entrain them to 24 hour(Vinod kumar et al.,2010;Chandrashekhar
et al.,1985). Day length interacts with the endogenous daily
photosensitive rhythms and regulates growth and development of
gonads. There is also evidence of endogenous circannual rhythm. This
causes evidence of photoperiodic response, there is also evidence of
the endogenous rhythmicity regulating gonadal cycles in few species
(Chandola et al.,1985;Vinod kumar et al.,2001).
has long been assumed that annual rhythms in reproduction and other
seasonal events are directly driven by seasonal proximate
factors, particularly daylength (Gwinner,1986). This concept has been
challenged in recent years and there is now a growing body of
evidence that in many long lived species seasonally changing
daylength interacts does not actively drive or induce reproductive
development, or rather acts as a zeitgeber to entrain an endogenous
circannual rhythm of reproductive function (Duston and Bromage, 1986).
Annual reproductive cycle for many species of fishes have
most frequently been described in terms of seasonal changes in the
GSI or histological changes in the testis or ovary (Peter and Crim
, 1979). The adaptive value of biological rhythms is tied at least in
part to their being synchronized to the light phases of the external
cycle, which in most cases in the light dark (LD)cycle of the
environment, in fact a stable and daily change in light
characteristics at dawn or dusk times serve as the most reliable
indicator phase of the day (Vinod kumar et al.,2002;
Chandrashekhar et al.,1985). By measuring
(Photoperiod) organisms are able to measure the passage of time and
coordinate their biological processes with favourable environmental
conditions (Sumpter, 1990). Environmental cues, particularly
photoperiod appear to have a more direct role than simply entraining
the clock to calendar time (Chandola and Singh, 1981).
advances in molecular biology have begun to clarify the role that
light plays in the timings of biological functions at a daily and an
annual level. This hypotheses is that light acts as an environmental
cue or "Zeitgeber" that entertains endogenous oscillation of
clock genes (Roenneberg and Merrow, 2003). Clock genes in turn
regulate other genes that require rhythmic daily expression. A number
of genes have been implicated in daily and circannual time keeping.
These processes and the genes involved are not completely understood
at present and their complexity varies across species (Dunlop,
1999). Because photoperiod has been shown to have a significant effect
on maturation spawning time and development in salmonids, circadian
rhythms genes are likely candidates for influencing the traits
clock and is common to both invertebrates and vertebrates (Stanewsky,
2003). It is accepted that light dark cycle of environment
synchronizes the biological clocks in most organisms which have
been studied (Chandola et al.,1985; Thapliyal and Chandola
entrains the rhythms via the circadian rhythm of melatonin secretion.
Further only a portion of the annual photoperiodic cycle is needed to
entrain the circannual reproductive rhythm; in this regard,
photoperiodic input during spring and summer is especially crucial if
thyroid hormones are absent during a restricted "Window" of time
around the end of the reproductive period in winter. A hierachy of
biological periodicities and multiple hormonal components of the
hypothalamus pituitary axis thus contribute to the regulation and
expression of the circannual reproductive rhythm (Stanewsky, 2003).
and Bromage (1991) reported the seasonally changing photoperiod might
have been expected to re-entrain the endogenous circannual rhythm
after exposure to continuous light, thus adjusting spawning back to
(2000) demonstrated that circadian rhythms are fundamental features
of all living organisms. The functional mechanism involved is built
around the internal biological clock and hormone melatonin one of its
critical components. The use of unusual light dark regimes and how
they are interpreted by the animal will help researchers to determine
if the circadian system is involved in measurement of photoperiodic
time (Turek et al., 1984).
are two types of skeleton photoperiods (Pitterdrigh, 1965). There are
'symmetrical' photoperiods in which each light pulse of the same
duration and there are 'asymmetrical' photoperiods in which the
light pulses are of different lengths although it is not known how
bright a light pulse must be to stimulate a response in fish
(Sumpter, 1990). However it has been shown that exposure to light of
low intensity can be effective (Bergman 1987). When using skeleton
photoperiods it is important without the second light pulse is
non-stimulatory (Baggerman, 1990).
from catfish suggests that the eyes and the pineal contribute to
synchronize the behavioural rhythms by a light dark cycle but that
the eyes and the pineal contribute to synchronize the behavioural
rhythms by a lights dark cycle but that other photpreceptors and
oscillators also contribute (Vinod kumar et al.,2001; Chandola
environmental cue most likely to influence biological rhythm is
photoperiod, biological rhythms have fundamental role privileging
individuals with capacity of anticipation of favourable-unfavourable
conditions (Marques, 2003).
growth, maturation and egg laying is controlled by hormones which in
turn are regulated principally by photoperiod (Stephens, 1952). In
seasonally breeding fish species altered fecundity fertility and
spawning intervals are associated with changes in environmental cues
such as photoperiod (Koger, et al., 1999).
Photoperiod strongly affected the timing of puberty and
sexual maturation (Norberg, et al., 2004). The photoperiod related
information is transmitted, via the pineal hormone, Melatonin
teleost fish, growth development and reproduction are influenced by
daily and seasonal variations of photoperiod and temperature. Early
in vivo studies indicated that the pineal gland mediates the effect
of these external factors most probably through the rhythmic
production of Melatonin (Falcon,e t al., 2003).
Photoperiod has a pronounced effect on the teleost pineal. The
functional relationship between the pineal and reproductive centers
may also therefore be dependent on day length. Melatonin treatment
inhibits the increase on gonadal size stimulated by long photoperiods
in Carassius (Fenwick, 1970 a).
process of photosensitivity are involved in the modulation of the
reproductive cycle in Rainbow trout and the circannual and circadian
rhythms co-operate in the timing and entrainment of reproductive
cycle (Duston, and Bromage, 1986). The annual gonadal cycle
consists of alternating periods of recrudecence and regression.
many fish species gonadal recrudescence and regression are to a large
extent controlled by the length of photoperiod (Baggerman, 1972).
Both photoperiod and temperature affected melatonin production in the
senegasole transducing seasonal information and controlling annual
reproductive rhythms (Vera et al., 2007).
1952 Stephens published a complex hypothesis of endocrine control of
the female reproductive cycle of the crayfish Orconectes virilis.
On the basis of eye stalk ablation, implantations of nervous tissue
and histological preparations of ovarian tissue she concluded that
four hormones controlled ovarian growth maturation and egg laying and
that the hormones in turn regulated principally by photoperiod.
suggest that genotype hormones and physiological conditions are
equally important endogenous regulators of growth (Dutta 1994).
Photoperiod would regulate the axis photoreceptor, pituitary
gonadotropin, ovarian estrogen secretion, oogonial proliferation and
endogonous yolk formation (Hansen et. al., 2001).
It was observed by Immelman(1963), that reproductive
cycles are affected by exogenous and endogenous environmental
cues. Gross et al.(1965), observed that fish growth and development is
also improved by increasing the photoperiod. The
circannual rhythms of hormones to be closely related with circannual
variations in ambient temperature day length and gonadal steroids
(Pavlidis et al., 2000).
seasonal periodicity is believed to be entrained by environmental
cues such as photoperiod and temperature (Leder, 2006). Many
poikilothermic animals use photoperiod to time seasonal events such
as migration and reproduction (Stephen, et al. 2000).
photoperiod regimes can be used to advance or delay the spawning
period and a year round supply of eggs can be ensured by replacing,
increasing and decreasing components of the seasonally changing day
length with periods of constant long and short day length (Taylor
and Migand 2008). Reproduction in most fish is typically a seasonal
process. Fish reproduction cannot be considered an exclusively annual
phenomenon because spawning may also show daily rhythmicity
(Meseguer et al. 2008). Photoperiodism is the ability of an organism to
assess and use the day length as an anticipatory cue to time seasonal
events in their life histories (Bradshaw and Helzafel, 2007).
and maturational events are dominated and coordinated by seasonal
changes in photoperiod, temperature, food supplies, rainfall, etc.
(Porter et al., 1998; Sanchez-Vazquez et al., 2000). Photoperiod and
temperature are generally considered the most important factors in
growth in fishes (Dutta, 1994). The effect of
photoperiod on teleostean reproduction are mediated via retinal
pathways and/or by extraretinal receptors. Electrophysical data
confirm that the teleostean pineal organ is a photoreceptor (Hanya
and Niwa, 1970).
melatonin daily rhythms provide the organism with photoperiod related
information and represents a mechanism to transduce information
concerning time of day. Photoperiod and temperature affected
melatonin production transducing seasonal information and controlling
annual reproductive rhythms (Vera, 2007). Pineal melatonin production
was clearly dependent on light perceived by eyes as opthalmectomy
resulted in basal plasma melatonin levels during the dark period
(Davie, et al., 2007).
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