Morphometry of Rhinomugil Corsula (Hamilton, 1822) From Sitakunda Coast of the Bay of Bengal, Bangladesh

A total of 65 specimens of Rhinomugil corsula (Hamilton, 1822), measuring from 8.1 cm to 28.9 cm in total length, collected from the Sitakunda coast of the Bay of Bengal, were used for the morphometric analysis during the period between March 2016 and February 2018. Twenty seven morphometric characters were selected and studied during the investigation period. The regression equations – both arithmetic and logarithmic – between the total length (TL) and 21 morphometric characters, and head length (HL) with five morphometric characters related to the head, were determined. The value of coefficient of correlation ‘r’ for each relationship was calculated and t-test for each ‘r’ value was also done. The relationships of the various measurements of the body with the total length – and head length with the five relevant characters -of R. corsula from the Sitakunda coast of the Bay of Bengal showed linear relationships, which were highly significant (P<0.01). The ranges of ‘b’ values 0.967 to 1.346 in case of the relationships between TL and 21 relevant characters, whereas 0.906 to 1.236 in case of the relationships between HL and 5 relevant characters. These values differ insignificantly (P>0.01) with typical value b=1 indicating isometric relationships among the characters. Bangladesh J. Zool. 49 (2): 229-241, 2021

Growth performance and cost-benefit analysis of brackishwater fin fishes (Mugil cephalus and Rhinomugil corsula) with prawn (Macrobrachium rosenbergii) in polyculture at coastal ponds

The study was carried out to observe growth, production and profit of prawn, stripped mullet (Mugil cephalus) and corsula mullet (Rhinomugil corsula) at different stocking ratio under polyculture in the Bagerhat district for four months. The experiment was designed as a randomized block design and had three treatments based on stocking ratio with three replicates in each treatment. Juveniles of prawn (Macrobrachium rosenbergii) and fingerlings of fin fishes (stripped mullet and corsula mullet) were stocked at a stocking ratio of 3:1:1, 4:1:1 and 5:1:1/m2 in T1, T2 and T3, respectively. Prawn and fin fishes were fed with a commercial diet and farm made formulated feed on a daily basis. Recorded water quality parameters were within suitable ranges of prawn and fish culture. Higher growth (43.0 g) of the prawn was achieved in T1 followed by T2 (41.0 g) and T3 (38.0 g), but prawn growth was not significantly different between T1 and T2. The growth and survival rate of prawn, stripped mullet and corsula mullet were lower in T3, where the stocking ratio was higher. Higher production of the prawn was obtained in T2 (1148.0 kg/ha) than those of T1 (954.6 kg/ha) and T3 (1083.0 kg/ha). But significantly (p<0.05), higher production of stripped mullet was found in T1 (650.0 kg/ha) and T2 (579.5 kg/ha) than T3 (500.5 kg/ha). Similarly, higher production of corsula mullet was found in T1 (850.0 kg/ha) and T2 (834.9 kg/ha) than T3 (719.8 kg/ha). However, combined production and net profit of prawn and fin fish farming were significantly (p<0.05) higher in T2 (2562.4 kg/ha, BDT 277,384.51/ha) followed by T3 (2303.3 kg/ha, BDT 229,693.95/ha) and T1 (2454.6 kg/ha, BDT 179,393.31/ha). So from a production and economic point of view, polyculture of prawn and fin fish at a stocking ratio of 4:1:1/m2 is more profitable compared to other stocking ratios and this system may be suggested to disseminate at coastal farmers’ level. J. Asiat. Soc. Bangladesh, Sci. 47(1): 67-78, June 2021

Length-Weight Relationships and Relative Condition Factor of the Mullet, Rhinomugil Corsula (Hamilton, 1822) In the Sitakunda Coast of the Bay of Bengal, Bangladesh

This study deals with the length-weight relationship and relative condition factor (Kn) of 2480 specimens of Rhinomugil corsula (Hamilton, 1822), ranging from 3.5 cm to 29.5 cm total length and 0.40 g to 235.34 g weight, sampled monthly for two years period from March 2016 to February 2018 from the Sitakunda Coast of the Bay of Bengal, Bangladesh. Arithmetic form of equations for length (TL) and weight (W) of fish showed curvilinear relationships in male: W=0.0081TL3.016, female: W= 0.0083TL3.058 and combined sex: W=0.0076TL3.052, while logarithmic scale showed linear relationships in male: LogW=-2.122+3.016LogTL, female: LogW=-2.09+3.058 TL and combined sex: LogW=-2.121+3.052TL. In all the cases the coefficient of correlations between length and weight were positive and highly significant (P<0.01). The regression coefficient ‘b’ values were found to be 3.01±0.11, 3.06±0.12 and 3.05±0.12 for male, female and combined sexes, respectively for two years period together. When ‘t’ test was done, the growth was found to be isometric in case of male and combined sex and positive allometric in case of female. The relative condition factor (Kn) varied from 1.0003-1.009, 1.001-1.008 and 1.001-1.008, respectively, for male, female and combined sex in 2016-17, whereas 1.001-1.007, 1.003-1.006 and 0.992-1.008 respectively in 2017-18. The Kn values were always around ‘1’ or a little bit more than ‘1’ for length groups as well as monthly, indicating the excellent growth and robustness of fish due to favorable environmental condition prevailing in the habitat of the fish, in the Sitakunda coast of the Bay of Bengal. Bangladesh J. Zool. 49(1): 91-103, 2021

Population dynamics of the mullet fish, Rhinomugil corsula (Hamilton, 1822), in the Sitakunda coast of the Bay of Bengal

Population dynamics of the mullet species, Rhinomugil corsula, was studied, using FiSAT-II program, with the length-frequency data of 2480 fish specimens. The asymptotic length (L∞) and growth coefficient (K) of this fish were estimated to be 31.4 cm and 1.0/year, respectively. The instantaneous rate of natural mortality (M), fishing mortality (F) and total mortality (Z) were estimated to be 1.73, 1.20 and 2.93, respectively. The recruitment pattern of the species was prolonged with two peaks, major peak during June to December and a minor peak during January to April. The L25, L50 and L75 were found to be 8.61, 10.42 and 12.23 cm, respectively. The relative yield per recruit (Yʹ/R) and biomass per recruit (Bʹ/R) were 0.751 and 1.731, respectively. The value of exploitation (E) was found to be 0.41 which indicated that R. corsula was not over fished (E > 0.50) in the study area. The maximum exploitation (Emax) value was 0.55. The growth performance index (ϕ´ = 2.99) of R. corsula in the Sitakunda coast of the Bay of Bengal was found to be moderate. Bangladesh J. Zool. 47(2): 305-314, 2019