Plankton composition, abundance and diversity in hilsa (Tenualosa ilisha) migratory rivers of Bangladesh during spawning season

Abstract

Hilsa (Tenualosa ilisha) is one of the flagship diadromous fish species of Bangladesh that migrate only through the Ganges-Meghna river system route. The biological profile of plankton from the Padma, Meghna and Tetulia reference river sites during 2011 spawning season of hilsa showed that in total of 58 taxa of plankton were present. Of which, 19 taxa (32.76%) were of phytoplankton and 39 taxa (67.24%) of zooplankton. Phytoplankton group belonged to Cyanophyceae (6 taxa), Chlorophyceae (7 taxa) and Bacillariophyceae (6 taxa) while zooplankton including Protozoa (10 taxa), Rotifera (19 taxa), Copepoda (4 taxa), Cladocera (5 taxa) and Ostracoda (1 taxon). The average abundance of plankton was recorded as 194.05 ± 82.58 indiv/l. The highest abundance of total plankton (692 indiv/l) was observed in Godagari, Rajshahi (Station 3) and was lowest (4.00 indiv/l) in Charghat, Rajshahi (Station 2). The highest abundance (49 indiv/l) of total zooplankton was observed in Godagari and lowest (1 indiv/l) in Charghat with mean value of 19.46 ± 4.12 indiv/l. The highest species richness (SR = 45) was observed in Daulotkhan, Vhola (Station 9) and the lowest (SR = 3) in Charghat (Station 2), with mean value of 17.10±4.408. Shannon-Weiner species diversity index (Hʹ) ranged from 3.334 in Daulotkhan (Station 9) to 1.5 in Charghat, (Station 2) with mean value of 2.717 ± 0.147. Based on the plankton profile it may be concluded that the biological quality of hilsa migratory river was not alike throughout the route which may restrict the migration up to up steam and spontaneous spawning of hilsa.

Assessment of Coastal Water Habitat with Reference to the Variability of Plankton during Spawning Season of Indian River Shad in Greater Noakhali-Bangladesh

“…No genera were identified under the group of crustacean larvae. In the current investigation, zooplankton contributed about 21% of total plankton abundance which differs from Ahsan et al [14] where they observed zooplankton population about 10% of total plankton. It can be said that in a lotic waterbody low population of zooplankton is not uncommon.…”

“…Shafi et al [13] reported higher percentage composition of phytoplankton (76.0 -93.6) % from the Meghna river. Similar findings were found in the recent investigation by Ahsan et al [14]studied on the plankton abundance of the Meghna river, observed that phytoplankton formed 90% of the total plankton abundance. water during the rainy periods.…”

“…It can be said that diversity index values of plankton are within the range of 1-3 indicates the moderately polluted environment of the Meghna River from the present study. There is a similarity found by Ahsan et al [14] where the pollution status of Hilsa migratory river resulted moderate pollution.…”

“…Coscinodiscophyceae and Dinophyceae resulted in no diversity in the study period because during observation only one species was recorded for both groups for that it nullify species diversity index. Ahsan et al [14] studied on plankton composition, abundance and diversity in Hilsha (Tenualosa ilisha) migratory rivers of Bangladesh during spawning season found the diversity 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 Species richness index (d) was also higher in Bacillariophyceae because there were about 22 species recorded belonged to this group and deliberately increased richness index. The species richness index (d) of Bacillariophyceae ranged from 2.00 (February, station-3) to 3.71 (June, station-4) with the highest mean value which was observed in June (3.10 ± 0.45) ( Table 5).…”

Tropical hilsa shad (Tenualosa ilisha): Biology, fishery and management

“…Even where hilsa is absent, these tributaries are closely coupled to the adjacent crop fields and villages, and are particularly influential in regulating and processing inputs of energy, nutrients and organic matters. These inputs contribute material to riverine food webs (Ahsan et al., ) and shape the structural characteristics of hilsa habitat in estuarine and marine ecosystems. Thus, hilsa‐less tributaries are hilsa habitat in much the same way as the rivers.…”