Correlation of some environmental variables with adaptive net-spinning strategies in stream larval Hydropsychids (Trichoptera) in Garhwal Himalaya (Short Communication)

Introduction The Hydropsychidae (Trichoptera) being the master spinners of freshwater rapids spin the net s of various sizes required during different seasons, and for different instars. Also they adopt strategies for coexistence between similar and different species by selecting various mesh sizes, current regimes, and habitat modes. The paper highlights the results of the study on the various net spinning strategies and associated environmental variables. In two larval hydropsychids from a small stream ‘Malethagaad in the Garhwal, Central Himalaya (India). Among net – spinning Hydropsychidae, the effect of certain seasonal environmental variables was studied and the most influencing ones recognised were water temperature changes, current speed, and increase in resource particulate concentration downstream. It was observed that in response to increase in all the above parameters (except temperature) net – spinning activity increases, reducing the size of mesh and thus successfully enabling the animal to adjust to the drag of the water current and particle filtration requirements with relation to the body size and microclimate of the dwelling mode. Certain anomalies were observed in hydropsychid capture nets from lotic sidewater pools and an increase in temperature probably also triggered an increase in net – spinning activity during summer, but the mesh shapes and sizes vary. Also probably the behavioural and morphological differences of various instars considered, facilitated in adaptive strategies for coexistence between similar and different species. Summary 1. The Hydropsyche k1 and Hydropsyche k2 divide up net spinning sites by partial differences in water velocity preferences, use of different dwelling crevices and modes of habitat. 2. The catch net mesh was found to be related to current speeds, resource particle requirements and the morphological stages of various instars and the combination of these variables may be taken as deciding factor as to how the mesh size is determined in a particular species to facilitate coexistence among different and similar instars of the same and different putative species. 3. Also the correlation of body size and net dimensions along with the distribution on the stream, with the increased resource particle concentration downstream and larger instars downstream point towards a natural distributional strategy enabling a successful species propagation for instars associated. Tropical Freshwater Biology VOL. 8 1999, pp. 27-3

AN INCIDENCE OF EYE AND SNOUT ABNORMALITY IN A HILLSTREAM MINOR CARP BARILIUS BENDELISIS (PISCES : CYPRINIDAE)

The paper deals with a report on an abnormal specimen of Barilius bendelisis (Hamilton) with an eye and snout abnormality. Morphometric characters of the abnormal specimen and its comparison with the normal fishes is discussed in the paper

LENGTH-WEIGHT RELATIONSHIP AND RELATIVE CONDITION FACTOR IN TOR CHILINOIDES (PISCES: CYPRINIDAE) FROM GARHWAL HIMALAYA

The paper deals with the length-weight relationship and condition factor in Tor chilinoides (Mc Clelland), collected from the river western Nayar of Garhwal Himalaya. The study indicated that there was a close relationship between length and weight. The value of regression coefficient 'b' was obtained 3.83 for males (r = 0.96), and 6.15 (r = 0.891) for females and 5.03 (r = 0.902) for pooled data. The higher values were either due to maturation of gonads during summer (4.12 for males and 6.94 for females) or due to the favourable feeding environment in winter (3.05 for males and 4.65 for females). The relative condition factor was calculated for T. chilinoides. The highest value for male fish was 2.122 + 0.1765 in the month of August and 1.988 + 0.1734 for the females in March. This entire period is a period of sexual maturity in fish. March is also a better feeding period due to favourable ecological parameters