Assessment of the impact of the water quality on ichthyological biodiversity in Morocco: Case of Oum Er Rabia River

Abstract

The objective of this work package is to identify and characterize the physicochemical and organic pollution parameters of the water along the Taghat - Khénifra section of Oum Er Rabia River during dry and rainy seasons (2018–2019) and their impact on ichthyological diversity. According to fish water standards parameters (Oxygen dissolved (8.17 mg/L), potential hydrogen (8.3), electrical conductivity (2647.5 µS/cm), Total Hardness (6.08 meq/L) and Sulphates (64.92 mg/L)). The different stations studied show that the parameters are in conformity with the needs of salmonids and cyprinids. For temperature, which is important for fish biology, the recorded values exceed the Moroccan standards for some freshwater species, and consequently the absence of salmonids in the study area (ST1 to ST4). The chloride concentrations are very high; these increases due to the water demineralization station and the lithology of the region may affect the growth of fish that must provide a lot of energy for osmoregulation. The main parameters of the organic pollution index (biological oxygen demand, chemical oxygen demand, ammonia, and nitrite) are in agreement with the needs of cyprinids only at stations ST1 and ST4. For ST2, which receives wastewater discharges without treatment and ST3, the water quality is poor for cyprinid especially for (varicorhinus maroccanus) endemic species classified according to the International Union of Conservation of Nature as a species listed in the red list. The results obtained corroborate with the fish river typology from the Oum Er Rabia River where the habitat of salmonids (Oncorhynchus mykiss and Salmo trutta macrostigma, Duméril, 1858) is limited only to the upstream part of the river. At all station (ST1, ST2, ST3 and ST4), density and biology of cyprinids are affected by the degradation of water quality following the discharge of wastewater, which will affect the socio-economic activities related to artisanal fishing and varicorhinus marocanus endemic species of Oum Er Rabia River.