INTRODUCTION
The fish of Rutilus frisii kutum is the most important bony fish
of South part of Caspian sea that more than 70% of catch fish by fishermen
in Iran coastal of Caspian sea consist of this fish.
Spring spawners arrive on the spawning ground in March to May. Due to
sharp decrease in stocking of R. f. kutum in Caspian sea
attempted made in artificial propagation of this fish for enhancing and
restocking. Much of the work performed dealed with quantitative purpose
and the production has been increased from 2 million in 1981 to 140 million
at present time. This effort made the possibility of harvesting up to
10000 ton in 2002 comparing to 1000 ton in 1981. The growing demand for
increasing sophisticated information of the effect of artificial propagation
of R. f. kutum has focused attention on the need for study of status
of this fish in different rivers. The present study will contribute toward
an improved understanding of some characteristics of breeders and normative
of propagation as well as some information about the quality of fingerlings.
The R. f. kutum is an order of cypriniforms representative of
cyprinid. Males normally mature between their third and fourth year, sometimes
earlier, females during their fourth year. Spawners are 3-8 years old
and the principal age groups are 4-5 years for males and 5-6 years for
females in the Anzali Mordab, older than the 3-4 years of fish reported
in 1970-1971. However, recently males are maturing at age 2 and females
at age 4 with most spawners at age 3 and 4 years, respectively. The commercial
catch in Iran was 3-7 years old, 39.0-57.1 cm long and weighed 613-2525
g (Coad, 1995).
Distinct sex characteristics make it easy to distinguish between mature
males and females. In the adult, the female has a large belly. The male,
if lightly squeezed around the belly will emit white milt. At spawning
time, very small plate covers the body of male and especially in the head
that is like a spot white. At this time the male is sufficiently different
from the female to allow for easy identification.
Natural habitat of this fish is only in the Caspian sea and is not found
in the lakes, rivers or fishponds. Feeding and nutrition of R. f. kutum
is consisting of zooplankton, phytoplankton, crustacean and mollusks.
In natural environment, the fish spawn in groups, in slow moving rivers,
at a temperature of 11-22°C. The eggs attach itself to vegetation
and sands and hatches within three days. In spite of high quality meet
of this fish, no cultivation of this fish are practice in pond. Economic
characteristic of R. f. kutum are listed as: high degree of fecundity,
high meet quality and rapid growth in natural habitat.
R. f. kutum suitable for spawning is catch in May and July from
the river and delta of a river. Most of fish selected from the river reproduce
easily but those are catching from delta and sea, are not able to spawn.
Presently, hormonal treatments for induced spawning are practiced in R.
f. kutum and are mostly based on the use of Carp pituitary (CP). Females
ovulated after one or two CP doses of 1-2 mg kg-1 b.wt. If
the whether is cold the female are injected 4-5 mg kg-1 b.wt.
and males after a single injection of 3-5 mg kg-1 b.wt. Spawning
of R. f. kutum was successful after a single injection of LH-RH
analogue (LHRHa), combined with pimozied. Mostly sufficient volume of
sperm is stripped without any hormonal treatment. Storage and sperm motility
are priority for successful artificial reproduction. Eggs for artificial
insemination were mixed together with sperm and immediately activated
in clean water of river. After 5 min, fertilized eggs are washed for 30
min with river or clean water eliminating the stickiness. No clay or talk
suspension is added to the fertilized eggs.
Fertilized eggs remain in jar without any shaking during early developmental
stage (for 2 h) and then incubated in siscrine incubator (cloth box) in
river (for 2-3 days). After that eyed stage eggs are incubated in 10 L
Weis jar. Hatching is expected 6 days after fertilization at 15-16°C.
The objective of this study are to introduce the biology and some aspects
of artificial reproduction of unique bony fish of Caspian sea, process
of restocking and the future status of this fish.
MATERIALS AND METHODS
The experiment were conducted at Shahid Rajaei Fish Complex and Ecological
Institute of Caspian sea, Department of Fish Genetic and Aquaculture at
Sari, Iran. Kutum were captured from four main river of Tajan, Shiroud,
Tonkabon, Goharbaran Rivers inlets to the Caspian sea during the spawning
migration in March-May 2002-2004 (water temperature 8-12°C).
To determination reproduction normative, about 30% of male and female
were sampled, every day during artificial propagation in 4-river station.
The brood fish were catching and individual brood fish suitable for stripping
were selected, kept separated in 50-tanks. Both male and female were checked
for spermiation and ovulation by gentle hand stripping. Female showing
large and soft abdomens were selected for spawning. Unripe female were
kept in wooden cage for 1-2 days for ripening. In practice, 2 males displaying
high sperm quality were used per female.
When eggs could be stripped easily, total eggs were collected in plastic
dry jar. Females were stripped only once. Oocytes and sperm were mixed
with feather. The clean river water was added and the mixture was gently
shaken for 1 min. After female ovulation, females were killed and the
remaining gonad was weight. All data about male and female, eggs, sperms,
fertilization rate, hatchery time and rate are scored.
Statistics
Results were calculated and plotted as Mean±SD. Comparison
and significance in difference between the normative of reproduction were
tested by one way ANOVA and followed by Duncan Multiple range test. The
level of statistical significance was set at p<0.05.
RESULTS
A total of approximately 42000 male and 15000 female were catch every
year. The breeders are three significant spawning categories involving
unripe, preripe, ripped (Fig. 1). A part of pre-ripe
are spawned, after keeping them 1-2 days in cage located in the river.
Approximately 75% of the immature fish that were transferred to temporary
cage without using any hormone reached maturity and spawned. In rivers
with mainly flooding current no installation of cage in the river is possible
and therefore only approximately 46% male and 58% female were used for
spawning. After selection of breeders artificial propagation were done
as following steps. The belly of the fish is wiped dry with cloth, then
a gentle pressure is applied to the belly to make the roe flow out. The
eggs of 3-5 females are released into 10 L plastic dishes, then the milt
of 5-10 fishes is added to the dish About 20 mL of fish milt is used to
1 L of eggs. The eggs are fertilized immediately upon their removal from
the female. The eggs and milt are thoroughly mixed by a feather, before
addition of water.
The fertilization is promoted by the use of clean water of the river.
Not any fertilizing solution or deadhesive material are used. The mixing
action is continuous for 2 min. At 2 min intervals, water is added to
the mixture. After 30 min, the water is poured off and fresh water is
added, it is repeated several times. The eggs are swell to 4 to 5 times
their original volume within 1 h and then are put in safety place for
2 h without any movement or shaking and then after rinsing the eggs are
placed in sisgren incubators. In the first 1-2 days the sisgren incubators
is to have a moderate flow of water and then at eyed stage, the eggs are
placed in hatching 10 L jar. The water temperature during hatching is
15-18°C. After three days of fertilization the flow are increased
to supply more oxygen for developing eggs. For preventing the generation
of fungus, the eggs are not treated by malachite green or any drug. Hatching
of the larvae is expected on the 6th day. After hatching, the hatched
larvae are transferred, to 240 L Zug jar. After 3 days, at starting active
feeding, by the time of yolk absorption the larvae are transferred to
05-2 ha.
The 3 years data of propagation of R. f. kutum are presented in
Table 1 biological and technological data.
From the total number of fish catched in the river from 2.1 male and
1.7 female one fish were selected as spawner. The highest number of spawner
(2560) was catch from Shiroud and the lowest number (510) from Tonkabon
river. The number of breeders catch in river was highly correlated with
the condition of weather turbidity of sea and river, the condition of
the delta of the river. In this respect, the wind direction, sea weaving,
direction of river flow to sea, turbidity of river were significant (p<0.05).
The average female catched were 37% heavier than male. Also total length,
fork length and standard length of male were shorter than female by 26,
28 and 14%, respectively. The smallest fish spawned had a 30 cm length
female and 25.7 cm male.
|
| Fig. 1: |
The diagram shows the total catch, spawned and kept
in cage for increase ripening at different time of spawning periods |
| Table 1: |
Biological and technological data of Rutilus frisii
kutum |
|
| Table 2: |
Comparing the sperm parameters of two main river of
South part of Caspian sea |
|
The temperature of water is an important factor in ripening and spawning
of fish. The temperature of the river was from 5 to 21°C and mostly
11°C. The average temperature of river was 11.16°C. Increasing
temperature from average 11°C to average 20°C showed significant
correlation with ripening of breeders and the correlation was positive
but low (r = 0.174). With increasing temperature in range of spawning
period, the brood stocks had a better potential for propagation. Out of
this range number of breeders reduced and the quality of breeders and
eggs were reduced as well as the weight of ovary.
The weight of ovary of 148 ovulated female were 165.7 g. The highest
amount of eggs (480 g) and lowest amount (42 g) were obtained from the
fishes of 3380 and 350 g, respectively. The most frequent breeders were
900 g fishes had a 146.7 g ovary. There was a high correlation between
the weight of ovary and weight and length of fish of r = 0.931, r = 0.913,
respectively. Number of dry eggs (eggs before fertilization and incubation)
was in the range of 216-434 and in average 320. The correlation between
weight of fish and number of eggs are storage and negative (r = -0.579).
Number of wet eggs per gram (4 h after fertilization) was in average 67.
That is in average for 4 river 33270 number per kg fish and 40723 per
fish. The fish that have good quality of sperm were used. For testing
the quality of sperm 100 fish were selected randomly and the following
items are measured (Table 2).
Fertilization is the main criterion for distinction quality of eggs and
sperm. The average fertilization rate of fish in four rivers was 85%.
The estimation of fertilization in Shiroud river was 92%, Tonkabon river
95%, Tajan river 75% and Goharbaran river 78%. The low rate of fertilization
in Tajan and Goharbaran is due to obtain breeders from delta or sea that
is not ripped enough. From total eggs for incubation 66% hatched and larvae
produced.
The eggs, during incubation, due to damage and unfavorable condition
of incubation become weak and having potential to fungi infection. The
management of farm and incubation is very important in this respect. Mortality
and fungi infection was 5-34% and in some special unfavorable condition
up to 100%. The absolute fecundity from 8604 fish sampling was 40723.
The minimum fecundity in Shiroud was 13768 but the average was 37651.
The fecundity is highly correlated and significant with length (r = 0.918),
weight (r = 0.849), age (r = 0.801) and the size of ovary (r = 0.952).
The relative fecundity is number of eggs per kg of fish. The average fecundity
in R. f. kutum was 33270. This amount is very close to absolute
fecundity that indicates the average weight of fish is about 1 kg. Minimum
relative fecundity was 22902 and maximum 10738, relative fecundity of
56538 had the highest mode between all the fish spawned. Relative fecundity
had a highly negative correlation with total length (r = -0.398), weight
(r = -0.422), age (r = -0.657) and the weight of ovary (r = -0.163) and
it was significant.
DISCUSSION
There are a series of changes in ecosystem of Caspian sea, e.g., fluctuation
of level of water, invention of Mnemiopsis leidyi (Yousefian and
kideys, 2003), changes in hydrology and hydrobiology of it. In the other
hand for several decades peoples have abused rivers using for disposal
of the wastes. Most of the rivers have proved unable to absorb the increasing
run-off resulting from poor watershed management resulting in increasing
flooding mainly due to change in land use within the basins including
deforestation, damming and accelerated drainage of urban and agricultural
lands. At the same time there has been a progressive loss of biological
diversity in the form of species or sub-species adapted to the former
regimes but unable to survive or endangering some of the native and unique
fishes such as R. f . kutom in the modified conditions.
In this respect we tried to report part of biology reproduction and normative
of artificial propagation of R. f. kutum, which is the highest
value bony fish of Caspian Sea.
Biological Aspect of R. f. kutum at Spawning Time
The adult R. f. kutum reach an average length of 45 cm, has
a slim cyrindial shape and is a vigorous swimmer. Distinct secondary sex
characteristics of male is not difficult distinguish between immature
males and mature males due to special white spotted spread on head and
sides of fishes (named as wedding spot).
The R. f. kutum is a semi migrating fish of south Caspian sea,
that for spawning migrate to the south river from end of winter to middle
of spring. Artificial reproduction is substitute of natural spawning due
to improper condition of the rivers. Unlike most of marine fish that can
spawn after induction hormones such as GnRHa, (Arabaci and Sari, 2004)
, in case of R. f. kutum most of breeders are riped enough for
propagation at the time of catching and are not to be stimulate with any
hormonal treatment except a part that is induce by using carp pituitary
extract or recently by using GnRHa combined with domperidone (Heyrati
et al., 2007). In this respect during 2002-2003 in average 12800
breeders (males and females) are catch for production of 305 million fingerlings
in earthen pond.
The survey of migration of breeders showed, up to April temperature in
average 10°C and more than 60% of breeders catch in river were not
ripped enough, they were kept in cage for further gonad development. By
increasing temperature (>11°C in April) most of fish catched was
ready for spawning however by increasing temperature from 18°C to
21°C, the quality of eggs decreased. The eggs shell become soft, gelatin
from and the rate of active larvae decreased significantly. Catching and
harvesting of fish in the river was also under many different factor effects.
Sometimes the delta was closed, or the seawater enter to the river, fluctuation
of river current and muddy condition was an other problem of R. f.
kutum migration.
The unstable condition of river and seas make the high variation in fish
quality and quantity in different rivers. The salinity, turbidity, temperature
are effect on size, type and quality of fish migrate for spawning. Therefore
high variation exists in normative of fish propagated in different rivers
and among the breeders. High turbidity and flooding of river make impossible
catching the breeders in the rivers, therefore the fish are catch by gill
net in delta of river, but they are not ripped enough. This reduces the
hatchability of eggs to 30-50%. Solving this problem, the fish that are
not of final stage of maturation, are transferred to cage fixed in the
side of river, provoke fish spawning and up to 65% of immature fish will
spawn 1-2 days staying there. Comparing number of dry and wet eggs per
kg of fish during last 5 years do not show any significant different while
the hatching rate decrease from 95% in 1998 to 85% in 2003, indicating
the rate of immature fish have been increased. As stated before a period
of incubation of R. f. kutum eggs, are spending in the river. Keeping
the R. f. kutum eggs in improper condition such as muddy condition
and salinity in a number of river stop eggs development. The average size
of mature females (700 g) has been decreasing.
Fecundity traits should only be considered in a breeding program if the
genetic correlation between egg size or egg quality with early survival
or growth rate is negative. It is, however, important to keep records
of these traits to study whether or not they are changing over a period
of time. Survey of absolute and relative fecundity between the years of
1973 and 2003 (Yousefian et al., 2003) showed that there are very
close number of absolute fecundity (56953 in 2002 versus, 58615 in 1973)
and no significant difference between them, while relative fecundity have
been changed from 74774 to 47352, it means the fish catch as breeders
are smaller in resent years comparing to 1973. Coad (1995) also repeated
that the average size of mature females (700 g) has been decreasing. Reduction
of average size of fish is due to selection of ripped fish taking the
eggs. Actually small fish will ripe earlier than bigger and ovulation
takes place faster than bigger fish. Approximately 72% of fish bigger
than 85% of fish smaller than 800 g spawn easily. Therefore trend of artificial
propagation is toward small fishes. This may affect negative selection
of growth rate, therefore selection response for growth rate are negative
and diminish some unknown rare gene and genetic drift. Actually losing
the bigger fish that need to stay more in the river for their genes characteristics
of late ovulation or late spawning genetics patterns is incorrect and
displeased part of the study.
With this system these fish are chose only if they ovulate easier than
the others and no regard is consider of other characters e.g., growth
rate, disease resistance, salinity resistance, etc. For solving the genetic
problem we suggested during hole period of spawning time, a port of all
breeders whether are small or large, should be propagate. If they are
not ripped yet, they will be kept in fibreglasses 2x2x1 near the river.
CP stimulates the permeation and ovulation injection intramuscularly at
doses 5 mg kg-1 b.wt. In this case females are stripped at
300-450 degree-hours post-stimulation.
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