Abstract: To study the reproductive biology of Liza abu, 360 samples of this species were collected during the period from February 2007 to January 2008. Reproductive characteristics of Liza abu showed that sex ratio is 1: 2.7 male to female, respectively. This means that females predominate males. Monthly variation in GSI of both sexes were quiet apparent. Maximum values were recorded in March (10.26 and 11.51% for males and females, respectively) and reached to the minimum levels in August (0.42 and 1.15% for males and females, respectively). These cyclic changes in GSI indices are considered as a proof that maturation season is started from January and spawning occurs in April. The maturity stages of male and female Liza abu are separated to 6 different successive stages. These stages in female are immature, resting, developing, developed, spawning (ripe) and post spawning. The testes maturation classified to virgin (immature), maturing virgin, maturing virgin, developing, developed, ripe and spent. The ova diameter ranged from 16.02 to 470.3 μ. It can be classified into transparent eggs ranging from 16.02 to 106.97 μ in diameter and yolked egg ranging from 126.82 to 470.3 μ in diameter.
INTRODUCTION
The mullets are found world-wide in temperate to tropical coastal waters readily entering estuaries and even resident in fresh waters. There are about 70 species but only 3 species are native to Iran in fresh and brackish waters. Some Mugil species have adapted to 100% freshwater while others to 100% salt water. One of the fresh water species is, Liza abu which is found in the Tigris-Euphrates and Orentes, river basin including the Tigris River basin in Iran, in the lower reaches of rivers draining to the Persian Gulf and in the Pakistan (Turan et al., 2004). Coad (1998) reported this species from the lower Hasan Langi, Kul, Gowdar and Mehran rivers at the straits of Hormuz in the Hurmuzgan basin, the lower Mand river and the lower Zohreh rivers in the Gulf basin, the Arvand, lower Karun, lower Kharkhe and the Simarreh rivers in the Tigris river basin. Most of the studies on this species have been carried out in Iraq and Turkey. In recent years, much research on Liza types and the mugilidae family have been conducted: Liza auratus` s reproduction biology in the ksilova (Messolonghi) lagoon in Greec (Hotos et al., 2000), reproductive biology and histological studies of the grey mullet, Liza ramada in the lake Timsah, Suez canal (El-Halfawy et al., 2003), Mugil seheli`s reproduction biology in fish farm (El-Halfawy, 2004). Compared to the biology and histology of reproduction of other fishes, less attention has been paid to the Liza abu as there is no published information on the reproductive biology and gonadal development of this species. The present study deals with the reproductive biology and histology of gonad of Liza abu in the water of Khuzestan Province.
MATERIALS AND METHODS
Monthly samples of Liza abu were collected during the period from February 2007 to January 2008 from dashte azadegan fishing center, which lies at 50 km west to Ahvaz. Length measurements of specimen were taken in centimeters and weight was determined in grams. To determine sexual maturity, gonads from male and females were weighed and morphologically examined. In order to determine time of reproduction, gonadosomatic index value for each month, were used according to the following formula:
GSI (%) = Gonad weightx100/Body weight (g) |
A piece of male and female gonad were fixed in formalin buffer 10% and proceeded with tissue processor and embedded in paraffin and sections, 5-7 μ thick, were prepared. Sections were stained with haematoxylin and eosin. Slides were examined with light microscope (Evans and Claiborne, 2006).The gonads maturation classified using criteria established previously for Liza ramada and Mugil seheli (El-Halfawy et al., 2003; El-Halfawy, 2004).
RESULTS
Sex Ratio
For Liza abu, the sex ratio of the collected samples was 1:2.7
male to female, respectively. This means that females predominate males.
The sex ratio is not constant throughout the different month: the highest
percentage of males is recorded of 40% in average during 5 month from
December to May. While the lowest average of 18% is recorded during seven
month from May to December, whereas the females have the highest average
percentage of 85% from May to September and the lowest percentage of 60%
in March (Fig. 1, 2).
Gonadosomatic Index (Reproductive Period)
Monthly variation in GSI of both sexes were quiet apparent (Fig.
3, 4). Maximum values were recorded in March (10.26
and 11.51% for males and females, respectively). A slight decrease occurred
in April for both sexes followed by a considerable drop in June (3.62
and 4.1% for males and females, respectively) and reach minimum levels
in August (0.42 and 1.15% for males and females, respectively). Thereafter,
the indices remained almost constant until December. From December, the
values increased. These cyclic changes in GSI indices are considered as
a proof that spawning season is lasting from February to June.
| Fig. 1: | Monthly variation of male percentages from February 2007 to January 2008 |
| Fig. 2: | Monthly variation of females percentages from February 2007 to January 2008 |
| Fig. 3: | Monthly variation of the average Gonado-Somatic Index of male Liza abu from February 2007 to January 2008 |
| Fig. 4: | Monthly variation of the average Gonado-Somatic Index of female Liza abu from February 2007 to January 2008 |
Histological Characteristics of Ovaries
Immature (Stage 1)
In this stage, the oocytes were small, with relatively clear zone
of cytoplasm. Cells diameter ranged from 16.02 to 52.22 μ. It was
weakly basophilic more than the nucleus in stain (Fig. 5).
Resting Stage (Growth Phase)
Two growth phase was observed in this stage. During the first growth
phase, the oocytes were mostly polygonal and varied in diameter from 55.05
to 79.14 μ. The nucleus ranged from 23.16 to 36.64 μ in diameter.
The nuclei were distributed in the nucleus irregularly and varying in
number from 2-5. In the 2nd growth phase, the oocyte reached to 106.97
μ in diameter. The nucleus increased in size and reached to 53.55
μ in the average with a numerous number of nucleolei about 8 to 11.
The nucleolei arranged in the periphery of the nucleus (Fig.
6).
Developing Female (Vitellogenic Stage)
During this stage yolk accumulation proceeded rapidly and obviously
increased the oocyte diameter. The maximum diameter of oocyte increased
to 382.3 μ and the nucleus appeared with diameter 87.51 μ in
average. Yolk granules were densely packed and occupied mostly the total
volume of the cytoplasm of oocytes. The zona radiate increased in thickness
varying from 2.2 to 2.07 μ and follicular epithelium was about 2.04
μ in thickness (Fig. 7).
| Fig. 5: | The ovaries in stage 1, small oogonia (OG) with one nuclei can be observed (X455, H and E) |
| Fig. 6: | The ovaries in stage 2, larger oocytes (LO) with numerous nucleolei in the periphery of the nucleus, can be observed (X455, H and E) |
Developed Female (Stage 4)
At this stage, the nucleus was migrating towards the animal pole and
contained many nucleoli. At the end of this stage, the nucleus became
amoeboid in shape. The nucleoli were scattered in the nucleus and ranged
in diameter from 70.56 to 78.32 μ. The wall of oocyte composed of
zona radiate a that reached to about 8.17 μ in diameter and follicular
epithelium recorded about 3.36 in average (Fig. 8).
Spawning Female (Stage 5)
At this stage, the oocyte diameter reached to 470.3 μ in diameter.
This represent the final stage of oocyte maturation. The nucleus could
not be seen and lost in the cytoplasmic mass beneath the animal pole.
The nuclear membrane disappeared and nucleus lost its shape and become
as nuclear material (Fig. 9).
Post Spawning Female (Stage 6)
At this stage, both atretic oocytes and immature oocytes of stage
1 and 2 was observed.
| Fig. 7: | The ovaries in stage 3, yolk vesicle (YV) are appeared around germinal vesicle (gv) (X 445, H and E) |
| Fig. 8: | The ovaries in stage 4, the nucleus is migrating towards the animal pole. The amoeboid nucleus (N) can be seen in this figure (X178, H and E) |
| Fig. 9: | The ovaries in stage 4, atretic oocyte (AO) and immature oocytes can be observed (X178, H and E) |
HISTOLOGICAL CHARACTERISTIC OF TESTES
Immature or Virgin Male (Stage 1)
At this stage, the testes were small in size and contained spermatogonia
which were the only cellular components (Fig. 10).
Maturing Virgin Male (Stage 2)
At this stage, spermatogonia and primary spermatocytes could be seen
easily. primary spermatocytes are smaller and have a dark nucleus. Males
in this stage is similar to resting females (Fig. 11).
Developing Male (Stage 3)
In this stage, intensive spermatogenesis was observed in the testes.
A decrease was observed in number of spermatogonia but an increased was
occurred in number of primary and secondary spermatocytes. In this stage,
secondary spermatocytes were the most visible cells in the testis (Fig.
12).
Developed Male (Stage 4)
In this stage, the testes lobules were larger. Cells of all stages
of development could be observed but secondary spermatocytes and spermatids
were the most numerous cells in the testes (Fig. 13).
Spawning or Ripe Male (Stage 5)
In this stage, the testes were filled with sperms (Fig.
14).
Spent Male (Stage 6)
At this stage, Residual spermatozoa and spermatogonia were observed
in the testes (Fig. 15).
| Fig. 10: | The testis in stage 1, spermatogonia (SG) can be observed which are the only cellular components (X 1780, H and E) |
| Fig. 11: | Testis in stage 2 (Maturing virgin), Primary Spermatocyte (PS) can be observed easily (X 1780, H and E) |
| Fig. 12: | Testis in stage 3 (Developing male), Primary spermatocyte (Ps) and secondary spermatocyte (Ss) can be observed easily (X 1780, H and E) |
| Fig. 13: | Testis in stage 4 (developed male) : Spermatids (Sp) are the most numerous cells in the testes (X 1780, H and E) |
| Fig. 14: | Testis in stage 5 (ripe male), The testes are filled with sperm (S) (X 1780, H and E) |
| Fig. 15: | Testis in stage 6 (spent male), Residual spermatozoa (S) and spermatogonia (SG) can be observed easily (X 445, H and E) |
DISCUSSION
In this study the sex ratio of Liza abu was 1:2.7 with 27.1 and 72.98% for male and female, respectively. This ratio was changed between different months but females predominate males. There is no published information on the sex ratio of Liza abu but we can mention similar studies which have been done on the other species. El-Halfawy et al. (2003) in lake Timsah lake found that the sex ratio of Liza ramada was 37 and 63% for male and female, respectively. Ilykaz et al. (2006) in Homa Lagoon found that the sex ratio of Liza aurata was 1:1.87 in favor of females. Spawning season of Liza abu in the water of the Khozestan Province extended from February to June on the basis of GSI values. According to this research, fish were ripe from January to May and spawned once during this period. Scientists have done several studies on the maturation of ovary in fish and based on the species classify it to 6 up 7 stages (Donalds and McMillan, 2007). There is no published information on the ovary maturation of Liza abu but we can mention results of histological studies on the other species. El-Halfawy et al. (2003) classified the ovary maturation of Liza ramada into 6 stages. El-Halfawy (2004) found stages in ovary maturation of Mugil seheli reared in fish farm. In this study, 6 oogenesis stages was observed in ovaries of Liza abu, which are as follow: In stage 1 (immature female), oocytes are small, this stage was observed from July to October. In stage 2 (resting female), considerable growth was observed in oocytes. This stage was observed from October to January. In stage 3 (developing female), due to vitellogenesis, the maximum growth is observed and three layers theca, granullosa, follicle cells are visible. The yolk deposition first appeared in the peripheral cytoplasm, thereafter scattered towards the center of oocytes as described by AL-Daham and Wahab (2006), Rustaisire and Booth (2004) and Çek et al. (2001). This stage was observed during January and February. In stage 4 (developed female), migration of germinal vesicle is observed and due to hydration of oocytes, their diameter is increased. The ovaries are yellowish and in maximum size and ovules can be easily observed with naked-eye. This stage was observed in February and March. In stage 5 (ripe female), spawning occurs. This stage was observed in April. In stage 6 (spent female), ovaries consist of immature and atretic oocytes and also empty follicles. Assem (2000) attributed the follicular atresia to environmental stress. This stage was observed in May and June. The maturation of testis for Liza abu in the present study was classified into six stages. There is no published information on the testis maturation of Liza abu but we can mention results of histological studies on the other species. El-Halfawy et al. (2003) classified the testis maturation of Liza ramada into 6 stages. Zaki et al. (1994) on their study on the seasonal histological changes in the testes of Mugil sehlei, classified the maturation of testes into 6 stages. Based on the results of this study, the stages of testes maturation of Liza abu are as follow: In stage 1 (immature virgin), the testes are small in size and contain spermatogonia which are the only cellular components. This stage was observed in August and September. In stage 2 (maturing virgin), spermatogonia and primary spermatocytes were visible. This stage was observed in October. In stage 3 (developing), intensive spermatogenesis is occurred and primary and secondary spermatocytes are the most visible cells during this stage. This stage was observed from November to January. In stage 4 (developed), cells of all stages of spermatogenesis could be seen but secondary spermatocytes and spermatids were in large number. This stage was observed from January to March. In stage 5, the testes were filled with sperms. This stage was observed in March and April. In stage 6, residual spermatozoa and spermatogonia were visible in the testis. This stage was observed from May to August. The analysis of the ova diameter in this study revealed that it varies between 16.02 to 470.3 μ. The ova diameter in stage 1 was 16.02 to 52.22 μ and increased to 106.97 μ at the end of growth phase. An obvious increased was observed in the vitellogenic stage and the maximum diameter was 382.3 μ. The increasing continued up to spawning with the average of 470.03 μ in diameter. There is no published information on the ova diameter of Liza abu but we can mention similar studies which have been done on the other species.
El-Halfawy (2004) reported the varying range of 0.1 to 0.7 mm for ova diameter of Mugil seheli. El-Halfawy et al. (2003) found that the ova diameter of Liza ramada was between 10-15 μ in stage 1 and between 500-700 μ in stage 4. Bαlgán et al. (2003) reported the average of 0.458-0.013 for ova diameter of Liza aurata. (Mc Donough et al., 2005).
CONCLUSION
Based on the results of this research, the maturation period of Liza abu in the water of the Khozestan province is started from January and spawning occurs in April. The sex ratio is calculated 1:2.7 (male to female, respectively) and females predominate male in all months. The Ova diameter varies from 16.02 μ in stage 1 to 470.3 μ in stage 4.