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Spawning Frequency and Sex Reversal of Tenualosa Ilisha (clupeid): a Review

BM Shahinur Rahman
Senior Scientific Officer
Bangladesh Fisheries Research Institute Riverine Sub Station, Rangamati, Bangladesh

Abstract/ Executive Summary:

Tenualosa ilisha (Clupeidae) is the most important single species and national fish of Bangladesh. It accounts for more than half of the total marine catches and about 12-13% of total fish production and about 1.0 percent of GDP. Absence of small females and large males and transitional gonads of the histological data proved Tenualosa toli and T. macrura (Clupeidae) changes their sexes at the end of the first year and spawn as females in the second year. T. toli Spawn in the middle reaches of estuaries and females deposit all their eggs at once while T. macrura spawn throughout the year in Sumatra but in Sarawak have a seasonal peak in the NE monsoon (December). The smaller sized T. ilisha are almost all males, a few small functionally female fish are present in Bangladesh water body. Male sex ratio of T. ilisha is less than female sex ratio (1:5.09).

Keywords: Sex change, Spawning frequency, Tenualosa ilisha, Clupeid

Location: Bangladesh Fisheries Research Institute Riverine Sub Station, Rangamati, Bangladesh

Start Date:

End Date:

Program Area: Animal Health and Management

Commodity: Hilsa

Objectives:

During last decades Hilsa fishery has been suffered by a combination of factors viz. serious growth and recruitment over-fishing. It is important to know spawning frequency and sex reversal of T. ilisha species for the management and conservation of this important single stock.

Methodology:

Sex change is a process by which a person or animal changes sex, by which female sexual characteristics are substituted for male ones, or vice versa. Generally Fishes or other animals changes their sex by two ways-Protandry: Where an organism is born as a male and then changes sex to a female. Ex: Tenualosa toli, Clownfishes (Amphiprion sp.) Protogyny: Where the organism is born as a female and then changes sex to a male. Ex: Large groupers (Serranidae), parrotfishes (Scaridae). Conducted a study in Sarawak Malaysia on Tenualosa toli (Clupeidae) and found absence of small females and large males, together with histological data showing transitional gonads, suggest that T. toli is a protandrous hermaphrodite.

Carried a study on Tenualosa macrura (Alosinae: Clupeidae): monthly from August 1996 until October 1998 throughout the estuaries and coastal waters of Sumatra and Borneo where it formed the basis of flourishing fisheries. They stated the evidence from sizes of sexes, sex ratios and histology is that T. macrura is a protandrous hermaphrodite. Most fish less than 200 mm SL were male, although a few females were between 135 and 200 mm. All fish over 210 mm SL were functional females. Carried a further study from January 1997 to December 2003 along the South China Sea coast of Sarawak and Sabah in Malaysia on Tenualosa macrura (Clupeidae) that indicate the sex ratio highly biased by length and most fish <20 cm were males whereas those >20 cm were females. Gonadosomatic index (GSI) and histological data of T. macrura indicate that Males mature at ≥10 cm and females at ≥20 cm. They found T. macrura is protandrous, but low numbers of small females suggest diandry.

Observed some aspects of the reproductive biology of Hilsa Shad, T. ilisha from the Persian Gulf (PG) and rivers of Khouzestan Province of Iran. A total of 485 fish were sampled by gillnet from Arvand (AR) and Bahmanshir (BR). Reproductive characteristics of T. ilisha showed that females predominate than males (M: F=1:2). Monthly variations in gonado somatic index (GSI) of both sexes were quite apparent. In PG, maximum values were recorded in April for male and female. Found sex ratio of Hilsa ilisha along the northeast coast of India 1:1.3. There was differential growth in sexes, the female having slightly faster growth. The ova diameter progression indicate single batch of ova only get segregated for spawning. They also indicate ovaries spent partially and fecundity ranged 467100 to 1369500 for 370-540 mm size fish. Stated that the male T. toli that are smaller in size usually change their sex to female at the size of 27 cm and weight of 600 g.

Spawning Frequency Spawning frequency is the numberof days between spawning. Spawning frequency was determined based on histological observation and two methods were utilized i.e. (a) the percentage of female in the late developing ovarian class with 0-h to 24-h postovulatory follicle (POF) in the ovary and (b) the percentage of female in the late developing class undergoing final oocyte maturation (FOM). Furthermore stated that spawning frequency was determined by dividing 100 (representing the total population of fish) by the percentage of fish with FOMs or POFs in the ovaries. Described ageing based otoliths of Tenualosa toli (Clupeidae) indicates that individuals may not live more than about two years. Male fish spawn towards the end of their first year, change sex (transitional gonads were recorded in fish from 14 to 31 cm SL) and spawn as females in their second year. Spawning takes place in the middle reaches of estuaries and females deposit all their eggs at once. Carried a study on Tenualosa macrura (Alosinae:Clupeidae): stated the evidence from sizes of sexes, most fish less than 200 mm SL were male, although a few females were between 135 and 200 mm. All fish over 210 mm SL were functional females. It changes from male to female mainly between 14 and 20 cm SL (standard length) (six months to one year in age), after the male has spawned. Almost all fish in their second year are females; the species does not appear to live beyond two years.

Source of Information: International Journal of Fisheries and Aquatic Studies 2020; 8(6): 131-136

Article Link (Online Journal): DOI: https://doi.org/10.22271/fish.2020.v8.i6b.2371

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The hilsa fishery generates employment and income for millions of people in India, Bangladesh and Myanmar. No comprehensive study regarding spawning frequency and sex reversal of T. ilisha has yet published. Thus it is important to know spawning frequency and sex reversal of T. ilisha species for the management and conservation of this important single stock. After this study the size and age of Tenualosa ilisha during sex changing period will be known; the spawning frequency of T. ilisha before and after sex change age will be identified as well as probable factors that influence sex change will be found.

Knowledge Management: Journal