Ecology of the fish food web in Dorudzan Reservoir, Fars Province

Abstract

Introduction: Describing the structure of the fish community food web and evaluating fish feeding interactions is crucial to understanding their impact on shaping the fish community and achieving sustainable fish production in the lake's biological management.
Materials & Methods: Samplings of phytoplankton, zooplankton, aquatic plants, and fish were performed at three stations near the dam crown, the middle of the lake, and the west of the lake for four seasons from October 2017 to September 2016. The fish caught were counted and bioassayed. Fish stomach contents and composition were assessed.
Results: A total of 43 genera from 30 families of phytoplankton of the lake were identified, from 11 classes and 8 phyla. Cyanophyta in autumn, Chrysophyta and Chlorophytain winter, and Chrysophyta in spring and summer were predominant. Eight species from eight families and three classes of zooplankton were identified. Benthic invertebrates were identified in five taxa (Chironomidae, Heptageniidae, Cyrenidae, Haplotaxida, and Nematoda). The identified species of aquatic plants were Myriophyllum spicatum and
Potamogeton nodosus. Eleven species of fish (Cyprinus carpio, Carasobarbus luteus, Alburnus mossulensis, Capoeta aculeata, Capoeta saadi, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis, Caressius gibelio, Ctenopharyngodon idella, Planiliza abu,
and Oncorhynchus mykiss) were identified in the lake. The maximum population size was recorded in P. abu (20,000 no/ha/12h). The most common fish food was detritus. Most fish showed omnivory and holistic approach and overlapped in food type. The diversity and complexity of the food web were maximum in autumn (33 communication chains), with maximum fish diversity and density, and the number of lake food communication chains was 40 throughout the whole year. The main chains of matter circulation to fish were
detritus, zooplankton, and filamentous algae in autumn, detritus in winter, fresh plants and detritus in spring, and detritus, fresh plants, insect, and zooplankton in summer.
Conclusion: This food web having short chains will result in lower fish biodiversity, which is already recognizable by the prevalence of the invasive species Planiliza abu and the drastic reduction in endemic species. For returning the lake ecosystem to equilibrium and
the best production, it is recommended that fishing methods be constrained to the use of smaller mesh size nets so that the fishing pressure is conducted toward P. abu, and makes it possible for the endemic species to rebuild their population.