The present study describes the associated relationship between the length-weight, sex ratio and related condition factor of Tenualosa ilisha based on the length and weight data collected from the commercial landing station of BFDC, Cox’s Bazar, from January 2019 to December 2019. The work was carried out on 866 specimens (307 male and 559 female) ranging from 8.4 to 53.6 cm in length and weight of fishes ranging from 7 to 1977g, respectively. The reproductive attributes of T. ilisha appeared in the sex proportions (M: F=1:2) which revealed the prevalence of females in comparison with males. The external observation was taken into consideration to determine the gender of Hilsa. The relationship of length-weight was fitted with the pooled data for males and females independently of all month-to-month samples which results the BW=0.0104TL2.9795 (R2=0.9636) and BW=0.0019TL3.4689 (R2=0.8461) respectively. The results expressed a higher correlation in between the length-weight (r>0.91). The length wise relative condition factor of T. ilisha was estimated as 1.02, 0.9, 1.05, 1.03, and 1.02 at the length group of 0-20, 21-30, 31-40, 41-50, 51-60 respectively indicating fluctuation of condition factor within the size group. The overall KR for T. ilisha was 0.9-1.22 in which maximum KR was found in July while the minimum was in March. The KR was strongly correlated with TL and BW.

A checklist of the native fishes of the Roktodaho beel of Adamdighi and Raninagar Upazila under the Bogura and Naogaon districts of Bangladesh, where data were collected monthly by field survey, focus group discussions, and personal interviews by using a semi-structured questionnaire and a pictorial check list of fish species from a professional fishing boat caught by different nets, traps, and hooks from July 2021 to June 2022. A total of 36 species under 8 orders belonging to 19 families were recorded, of which 29%, 28%, 25%, and 8% were available, seasonal, rare, and very rare, respectively. Among those, 8 fish species (22.22%) were in the threatened category (1 critically endangered, 2 endangered, and 5 vulnerable), according to the IUCN Bangladesh. Notably, the globally threatened Channa orientalis and Wallago attu were available in the study area. According to their place of residence, 24 (66.67%) of the fish were floodplain residents except Glossogobius giuris, which is a mixed residence (reverine, estuarine, and floodplain) species. This residence status of fish indicates that the species have chosen their ideal environment. Dewatering, katha fishing, and the use of unlicensed technology were the main dangers. Creating and maintaining fish sanctuaries, reducing human effects, passing fishing regulations, and increasing consciousness may all help to preserve the current supply of fish. Strategies for restoration must be performed in the Roktodaho beel to preserve the fish range.

This study was conducted to evaluate the culture potentiality and growth performance of Spirulina (Spirulina platensis) in supernatant digested rotten guava (DRG) in replacement of Kosaric Medium (KM). The Spirulina was inoculated to grow in digested rotten guava media (DRGM) (treatments) with the addition of 9.0 g/L NaHCO3 and micronutrients and KM for a period of 14 days. The cell weight of spirulina was attained a maximum of 12.43±0.20 mg/L (dry wt. basis) in KM followed by 0.818 ± 0.003, 0.815 ± 0.0015 and 0.809± 0.0012 mg/L in supernatant of 60 (T1), 20 (T2) and 40% DRGM (T3), respectively on the 10th day of culture. The cell weight of spirulina grown in these media had highly significant (P<0.01) correlation with the chlorophyll a content (r = 0.746) and total biomass (r = 0.742) of Spirulina. The results showed that the growth performance of spirulina in supernatant of 60% DRGM was significantly (P<0.01) higher than that of spirulina grown in supernatant of 20% and 40% DRGM. The physico-chemical parameters viz. light intensity (2748 to 2768 lux/m2/s), temperature (19.0 to 22.2°C), pH (8.1 to 10.6), alkalinity (1522 to 2698 mg/L), nitrate-N (1.25 to 3.64 mg/L) and phosphate-P (11.30 to 55.40 mg/L) were within optimum level during the culture period. The results showed that, the different concentration of digested rotten guava (20%, 40%, 60%) has potential to increase the growth rate of Spirulina. Therefore, the DRG medium may be commercially used for mass culture of Spirulina platensis.

This experiment was inquired to apprehend the associated relationship among the cell weight, chlorophyll a and total biomass production of Spirulina platensis grown in different concentration of digested rotten guava medium (DRGM) and kosaric medium (KM). This study was carried out to disclose the culture potentiality of different substrates and their impact on production through the assessment of their consequential correlation. The completely randomized design (CRD) was taken into consideration to accomplish the experiment in laboratory condition. The maximum cell weight was assumed in KM (12.41 ± 0.23) followed by 0.816 ± 0.0017, 0.813 ± 0.0013 and 0.807± 0.0011 mg/L in supernatant of 60%, 20% and 40% DRGM, respectively on the 10th day of culture. The correlation (P< 0.01) with the chlorophyll a content (r = 0.745) and total biomass (r = 0.741) revealed significant association and strong correlation with the obtained cell weight in these culture media. In kosaric medium, the growth performance was significantly higher (P<0.01) than that of grown in the different concentration of DRGM (60%, 40% and 20%). The content of chlorophyll a grown in KM (10.54 ± 0.33 mg/L) was significantly higher (P< 0.01) in comparison of 60% (0.863 ± 0.0018), 40% (0.769 ± 0.0015) and 20% DRGM (0.771 ± 0.13). The highest biomass of S. platensis was acquired in KM (705.52 ± 2.59 mg/L) and varied significantly (P < 0.05) than that of cultured in supernatants of 20% (67.76 ± 0.42), 40% (51.45 ± 0.26) and 60% (57.74 ± 0.26) DRGM. The culture techniques in DRG medium may dwindle the cost of production in comparison with KM and might be considered as a media for Spirulina platensis cultivation.

The study was intended to assess the impact of fishing enclosure during the peak breeding time of hilsa, Tenualosa ilisha on its breeding success. During the last peak breeding season of hilsa (October 4-25, 2021) a comprehensive investigation was attempt to evaluate the impact of fishing enclosure by “MV Rupali Ilish” research vessel, speedboat and experimental fishing net were deployed to demeanor a rigorous investigation in and around the spawning grounds areas (about 7,000 sq km, including Moulvirchar, Monpura, Dhalchar and Kalirchar). Additionally, data were also assumed from landing stations (via terrestrial cruises) near the spawning ground areas and other hilsa prone region of Bangladesh. The percentage of spent hilsa (locally called pite) and oozing hilsa were monitored following a standard protocol. Among all the hilsa captured in and around the spawning grounds, the proportion of male and female were 16-41% and 85-97%, respectively of the total catch, suggesting a male and female sex ratio (1:2.3). The rate of breeding success in 2021 was 51.76% i.e., 51.7% hilsa successfully participated in the breeding process which was 103.52% higher than the base year (2001-02). The approximate number of fertilized eggs in 2021 was 7,86,314 kg. Increased production of hilsa eggs and jatka indicated a positive impact of twenty-two days fishing enclosure. Percentages of gravid and oozing hilsa were also found higher compared to previous years. Due to the prohibition of all types of fishing, the percentage of female hilsa in the breeding areas increased up to 83.96%. Overall, twenty-two days fishing enclosure was found very effective for successful spawning of hilsa.