BIODIVERSITAS ISSN: 1412-033X Volume 21, Number 9, September 2020 E-ISSN: 2085-4722 Pages: 4022-4033 DOI: 10.13057/biodiv/d210913 Distribution of zooplankton community in Toli shad ( Tenualosa toli) habitats, Sarawak, Malaysia WAN MOHAMAD AIMAN 1 , FATIMAH MD YUSOFF 3 , AZIZ ARSHAD 3 , ABU HENA MUSTAFA KAMAL 2,♥ , JOHAN ISMAIL 1 , MOHD HANAFI IDRIS 2 , NURUL ULFAH KARIM 2 , ABDULLA AL ASIF 1 1 Department of Animal Science and Fishery, Faculty of Agriculture and Food Sciences, Universiti Putra Malaysia Campus Bintulu. Nyabau Rd, 97008 Bintulu, Sarawak, Malaysia 2 Faculty of Fisheries and Food Science, Universiti Malaysia Terengganu. 21030 Kuala Nerus, Terengganu, Malaysia. Tel./fax.: +60-9-6685001, ♥ email: a.hena@umt.edu.my 3 Department of Aquaculture, Faculty of Agriculture, Universiti Putra Malaysia. Serdang 43400, Selangor Darul Ehsan, Malaysia Manuscript received: 25 April 2020. Revision accepted: 10 August 2020. Abstract. Aiman WM, Yusoff FM, Arshad A, Kamal AHM, Ismail J, Idris MH, Karim NU, Asif AA. 2020. Distribution of zooplankton community in Toli shad (Tenualosa toli) habitats, Sarawak, Malaysia. Biodiversitas 21: 4022-4033. The river ecosystems of Sarawak has been identified as important-spawning ground for economically important Toli shad (Tenualosa toli) fisheries. In these river ecosystems, zooplankton serves as a secondary producer to the different types of fish larvae including Toli shad. The productivity and biomass of zooplankton are important factors to control the production of higher trophic level organisms like fish larvae and fishes in different stages including T. toli larvae. In this viewpoint, the composition and abundance of zooplankton were investigated at 5 (five) sampling stations (considered to be spawning and nursing areas of Toli shad) at Batang Lupar and Batang Sadong estuaries from July 2016 to June 2017. A total of 29 zooplankton taxa were recorded that belong to 14 major groups comprised of Copepoda (Arthropoda), Crustacean nauplii (Arthropoda), Fish larvae (Chordata), Mollusca (Mollusca), Luciferidae (Arthropoda), Cnidaria (Cnidaria), Ostracoda (Arthropoda), Cirripedia (Arthropoda), Polychaete larvae (Annelida), Chaetognatha (Chaetognatha), Appendicularia (Chordata), Amphipoda (Arthropoda), Echinodermata larvae (Echinodermata) and Cladoceran (Arthropoda). Copepod was dominant group of zooplankton (82.40- 94.41%) at all stations, contributing 477.37-25921.89 ind/m 3 and 88.38% of total abundance. The second highest was crustacean larvae (2.45-9.38%) in all stations, contributing 0-2391.7 ind/m 3 and 5.88% of total abundance. Zooplankton abundance was higher at downstream station 1 (8460.72 ind/m³) followed by station 2 (5479.80 indi/m³), station 3 (4571.95 ind/m³), station 4 (4394.20 ind/m³) and upstream station 5 (4156.73 ind/m³). Canonical Correspondence Analysis showed that the abundance of copepods was highly influenced by total turbidity and nitrate in the riverine and estuarine ecosystems. Abundance of zooplankton was relatively higher (9549.31 ind/m³) during the post-monsoon and lower (3534.56 ind/m³) during the southwest monsoon. Keywords: Malaysia, Sarawak, Toli shad, Tropical Borneo, zooplankton INTRODUCTION The presence of zooplankton is the key indicator of the healthiness of a water body (Ismail and Adnan 2016). It also plays a significant ecological role in the food web in any aquatic ecosystem (Cook et al. 2007). It recycles micro-macro nutrients including organic matter transformation (Edwards, 2001) from primary producers to secondary consumers like fishes (Thirunavukkarasu et al. 2013). High-value commercial fishes mainly Toli shad (Tenualosa toli) used to migrate turbid and brackish estuary (Mohsin and Ambak 1996) for spawning and nursing in Sarawak waters, Malaysia, where zooplankton community plays a vibrant role for nourishment to different commercial species up to juvenile from larvae including Toli shad (Tumiran et al. 2011; Rahim et al. 2014). Studies showed that the seasonal distribution and abundance of zooplankton represented in dissimilar patterns throughout the season in a year elsewhere (Srichandan et al. 2013; Buttay et al. 2015; Marcolin et al. 2015; Abu Hena et al. 2016; Abdullah et al. 2018). Estuaries are usually non-isolated and highly tidal region with the change of all physicochemical parameters that influence the planktonic food sources for fishes found in tropical estuarine ecosystems (Harrison 2004; Hossain et al. 2012; Saifullah et al. 2014; Paturej et al. 2017). Previously, Chew and Chong (2010); Rezai et al. (2011); Lee (2012); Zaleha et al. (2013); Zulikha et al. (201)3; Kassim et al. ( 2015); Matias-Peralta and Yusoff (2015); Musa and Singh (2015); Azmi et al. (2016); Fatema and Omar (2016); Saidin (2016); Yong et al. (2016); Kamaruzaman et al. (2018) had documented the seasonal distribution of zooplankton from both the riverine and estuarine water of Malaysia. Although several studies have been undertaken in Peninsular Malaysia, a few zooplankton studies dealt in the estuarine and riverine habitats in east Malaysia (Jivaluk 1999; Johan et al. 2013; Sinev and Yusoff 2015; Sinev and Yusoff 2018). Furthermore, there are no previous studies revealed on the temporal population structure of zooplankton in Sarawak riverine and estuarine waters, which is very well known for the historical T. toli shad spawning (Rahim et al. 2014) and nursery ground. Considering an important breeding area of a high valued