Length-Weight Relationships for the Benthic Invertebrates of a Mountain River in the Southern Caspian Sea Basin, Iran

Biomass is an important parameter in studying a variety of energetic processes in food webs, community structure, and composition of aquatic organisms. Biomass determinations are based on direct weighing of animals, biovolume determination, and length-weight conversion. Although direct weighing of individual organisms is the most accurate methodology, its application is not very common due to its time consuming nature. Length-weight regressions are the most widely used approach for estimating benthic invertebrate biomass because they are less time consuming and more precise than other methods. In this research, length-weight relationships are evaluated for the most common benthic invertebrates found in an Iranian mountain river in the Southern Caspian Sea Basin by fitting the power function (linearized by logarithmic transformation) to data of wet and dry weights against body length of aquatic invertebrates at both family and order level. A general predictive equation was also obtained for all individuals measured in this study. Regressions obtained were significant at a P value of < 0.05 and explained a high proportion of variation of the dependent variable, as expressed by the correlation coefficient (r= 0.82-0.99). Regression equations obtained in this study for three major orders of aquatic invertebrates were also compared to those in previous studies from different geographical locations. Relationships developed in this study, can be useful for future assessments of benthic community structure and for understanding the importance of these invertebrates in the energy flux of the river.