Synchronicity of Condition Factor with Reproductive Development in Rainbow Snakehead (Channa bleheri Vierke, 1991)

Channa bleheri, also known as rainbow snakehead is a colourful Channid species distributed in certain pockets of Dibrugarh, Tinsukia district of Assam and Dikrong River in Arunachal Pradesh, India (Vishwanath and Geetakumari, 2009). The species has been assessed as Near Threatened in the IUCN Red List of Threatened Species (Chaudhry, 2010) due to its overexploitation in aquarium trade and anthropogenic impacts on their natural habitats. Kalita et al., (2018) reported that the increasing demand of this fish for the ornamental trade both for the domestic and overseas markets has lead to the rapid decline of their populations from the wild. National Bureau of Fish Genetic Resources (NBFGR), India, enlisted the fish as one of the endangered species of India (Lakra et al., 2010). These existing threats lingering upon the species necessitates time bound intervention to restore its population in their natural habitat. Development of the gonadal stages at different season has direct impact on the fish condition (Barnham and Baxter, 2003). Cube-law describes a classic method of determination of fish condition in respect to different life stages, sexes, stages of gonad development and different seasons (Le Cren, 1951). Fishes, before and after reproductive, begin to show a marked departure from the cube law and that changes arising from season changes and body sizes. Attempts have been made to understand the gonadal changes in few Channa species (Parmeswaran and Murugesan, 1976; Srivastav et al., 1998, Al Mahmud et al., 2016; Milton et al., 2017). As growth pattern and condition is directly correlated with length and weight of fishes, development of gonads ought to have influence on these parameters.

Sample collection
 
Experimental fishes were collected from different water bodies of Dibrugarh and Tinsukia district of Assam, India. A total of 283 specimens were taken under study.
 
Condition factor (K)
 
K factor was determined following Ricker (1975):

 
 

Where
W= Fish weight in g.
L= Total length in cm.
 
Gonado-somatic ratio (GSR)
 
The gonado-somatic ratio is calculated for each month using following formula. At least 7 number of male and female each month was taken under study:

 
 

 
Histology
 
For histological studies the sections of the gonads were fixed in 10% buffered formalin solution at room temperature. Small pieces of ovary (6-8 mm) and testicular follicle (4-6 mm) were fixed in Bouin’s solution for 48 h and subsequently processed for histology following Degani (1994). The central portion of the gonads was taken for histological examination which was put in different cassettes. The sections were then dehydrated through increasing grades of ethanol (30%, 50%, 70%, 90% and absolute ethanol) and then clarified with xylene. The samples were then embedded in paraffin blocks and sectioned at 4-5 µm thickness using a semi-automated microtome. Two types of stains were used in the process viz. eosin and haemotoxylin followed by periodic acid Schiff (Milton et al., 2017). After mounting in DPX the slides were examined and photographed under LEICA DM 750. The developmental stages of gonads were observed under the microscope as immature, maturing, mature and spent stages (Navarao et al., 1989).

The stages of gonadal development are described in Table 1 and are divided into five stages as was found in Mystus montanus (Arockiaraj et al., 2004) and Channa gachua (Milton et al., 2017) i.e. Pre-mature (Immature), Pre-spawning (maturing), Pre-spawning (mature), Spawning (ripe), Post-spawning (spent). The gravid stages were found from April to June which is the potential time of breeding of this species (Stage IV). Spent stage was observed in the end of July and August (Stage V), while maturing ovary appeared in the months from September to January till the end of February (Stage II). From the end of February and March mature ovary was found (Stage IV). The stages found in Channa bleheri correspond with the stages were also reported by various workers (Kesteven 1960; Navarao et al., 1989; Arockiaraj et al., 2004; Milton, et al., 2017).
       
Fulton (1904) laid the concept of allometry in fishes that is influenced by the increase in weight in respect to length during spawning season. There is a gradual increase in the value of condition factor as well as gonado-somatic ratio (GSR) from April to June as shown clearly in Fig 1, 2 and 3. The weight of the fishes is directly related to its condition factor value with highest value attained at the time of spawning (Wege and Anderson, 1978). Use of histological studies in estimating the gonadal stages in fishes had become more reliable and consistent (Tomkeiwicz et al., 2003). On observing microscopically four different stages of gonads were found as was also found in Channa striata (Al Mahmud et al., 2016) and Channa gachua (Milton et al., 2017). There is a gradual increase in the value of condition factor as the fishes approached spawning season (Froese, 2006). Histological examination showed that the chromatin nucleolar, early peri-nucleolar and late peri-nucleolar stages in female appeared early when the GSR value was low in September to December (Fig 4, 5 and 6), while spermatogonia and spermatocytes appeared from December to Early February (Fig 12 and 13). Advanced stages like yolk globular and yolk vesicular stages appeared from late February and March (Fig 7, 8 and 9), while spermatids started appearing in male. The mature stages i.e. yolk granular stages in female (Fig 10 and 11) and spermatids and spermatozoa started appearing from April to June (Fig 14 and 15). There was a significant difference in GSR value for samples collected in different months (P<0.05). The systematic rise in the GSR values in both the sexes prior to breeding season with prominent increase in females from January to March (Fig 2 and 3) was synchronous with histological gonad development in the two sex.
 

 

 

 

 

 

 
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The gonad condition of Channa bleheri that was found throughout the year is presented in Table 1.

From our study it is observed that gonad development has close relation with the growth pattern and condition factor in C.bleheri. The understanding of developmental changes in a species will open new insights about the species. The data generated in our study hope to develop better management strategies for conservation of this important species.