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Article Type

Research Article

Subject Area

Fisheries Science

Abstract

During the last century, Lake Qarun witnessed successive ecological changes and diverse exploitation patterns. Recently, by 2015, a vigorous invasion and spreading of an exotic crustacean isopod resulted in a massive mortality of lake fishes. For crisis management, administrative bodies adopted two low risk approaches; dredge the area near the entrance of main drainage and stop the regular annual lake stocking with fish fries, to improve water quality and interfere with the parasite life cycle. By 2021, proposing an effective plan for rehabilitation and restoration of the lake Qarun ecosystem was an urgent demand. Thus, determining the present status of fish stocks that still survive in the lake was a priority, through designing a comprehensive fishing survey, from September 2021 to September 2022. Surveys' results revealed that Egyptian sole, anchovy, and small shrimps are the aftermath survivors. Considering the economic importance of Egyptian soles, its current population characteristics studied in detail (length-frequency distribution, length-weight relationship, sex-ratio, age determination, age-length-key). Size-frequency distribution compared between the three different sectors of the lake. Screening the history of Egyptian soles population in Lake Qarun indicated that soles was the only commercially important fish species that withstand all consequences of ecological changes in the lake, since its appearance in the catch by 1948. To discuss the eligibility of Egyptian soles as an ecological indicator for Lake Qarun, recent size-frequency results compared with previous studies concerned species in Lake Qarun, through applying a simple reliable nonparametric statistical test. The comparison indicated that Egyptian soles is eligible as an ecological indicator for Lake Qarun ecosystem, and it should be highly considered in any fisheries development plan. Moreover, the high incidence of anomalies and malformation among the sole population in the lake compared to the rare incidence for wild population in other localities proposed its eligibility as an environmental quality indicator for the different lake fishing sectors. A well-designed stock enhancement program is recommended to support the existing Egyptian sole population in Lake Qarun. Concerning prevalence of cymothoid isopod parasite, present study revealed a sharp decline in its morbidity among sole fish compared to the single study carried out from 2014 to 2016.

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