The researchers studied the fish population in Al-Huwaizah marsh in Iraq. They collected fish samples monthly for a year and found 19 different species, some native and some alien. The most common species were Planiliza abu, Coptodon zilli, and Carassius auratus. They caught a total of 2,190,680 tan of fish, with the highest weight in July and the lowest in September. The diversity, richness, and evenness of the fish population were calculated. They also looked at factors like water temperature, dissolved oxygen, salinity, and pH. The researchers used Jaccard Similarity Index to compare monthly catches and Canonical Correspondence Analysis to understand the relationship between fish distribution and environmental factors.