Determining nutritional indices of Dori bleak, Alburnus doriae and Brond Snout, Chondrostoma regium in Zayandehroud River, Central Iran

Introduction: Zayandehroud River is one of the most important permanent freshwater rivers in the central part of Iran. Studying aquatic organisms, especially endogenous fishes, could be useful for understanding biological and ecological processes. Among the fishes in the Zayandehroud River, Dori bleak, Alburnus doriae and Brond Snout, Chondrostoma regium, belong to the Cyprinidae family. They exist in this river in the middle and upper parts with sand and gravel habitat. They usually feed on insects and other aquatic invertebrates. The gut content analysis is one of the most widely used methods for identifying fish's food and feeding habits. Studying the diet contents is the main key to understanding many aspects of biology, ecology, physiology, and behavior of fishes. In addition, the nutritional position in the ecosystem, feeding habits, and relationship with other species could be influenced by dietary regimes in the aquatic resources. The purpose of this study was to determine the type of diet and feeding habits by analyzing the gut contents of A. doriae and C. regium and measuring some nutritional indicators. The findings of this study could be used to protect biodiversity and provide a better understanding of the structure of food web in Zayandehroud River. Materials and methods: Fish sampling and some physicochemical water parameters were carried out seasonally during the spring, summer, autumn, and winter of 2012 from two sampling areas of Cheshme Dimeh and Khersonek of ​​Zayandehroud River. After separation, the eaten food items were identified and classified, counted, and weighed at the lowest possible systematic level using identification keys of aquatic invertebrates. The indicators of the vacuity index, relative length of gut, and Ivlev's electivity index were used to check the nutritional conditions and determine the importance of different food groups. The obtained data was analyzed using SAS 9.3 and Excel 2013 statistical software. In addition, the changes in the vacuity index were determined using the chi-square test. The One-Way ANOVA was used to determine data statistically significant differences. Results and Discussion: The vacuity index was 11.5% for A. doriae and 24% for C. regium. The highest value of this index for both species was in autumn, while the lowest in winter. This index significantly differed throughout the year for both species (P<0.05). The average relative length of gut was 0.73 ± 0.08 and 1.36 ± 0.24 for A. doriae and C. regium, respectively. There was no significant difference between the relative length of the gut in different age groups throughout the year in both fish species (P<0.05). The Ivlev's electivity index showed that A. doriae had a greater tendency to feed on the Odonata, Plecoptera, Coleoptera, Hemiptera, Arachnida, and Hirudinea, while C. regium had a higher feed tendency for Plecoptera, Odonata, Ephemeroptera, and Hirudinea. The seasonal changes in the nutritional indexes could be related to food availability in the environment. In addition, high values ​​of the vacuity index in fish can be changed by daily feeding of fish, reproductive activity, and prey availability. The relative length of the gut varies according to the type of food consumed by the fish, the amount of plant material in the diet, the species, and different life stages of the fish. Conclusion: The results demonstrated that A. doriae and C. regium are carnivorous and omnivorous, respectively. A. doriae prefers insects, but C. regium consumes mostly insects and filamentous algae as the preferred food. The seasonal differences in these two species' diets occur due to differences in food selection in Zayandehroud River.