Study of density, distribution and yield on benthic fauna and brown trout (Salmo trutta fario) feeding in Laar reservoirs

Lar lake, with the international UTM specification of 39S 579680 3976567& 39S 589930 3976184 is Situated in Lar national Park with an aerial distance of 55 Km ofTehran along Haraz road.The present research is carried out as part of a comprehensives Plan for assessment ofbioresearches of Lar lake & the rivers flowing into it. This research includes examination ofthere benthic Samplings performed in Lar lake and each of the related rivers includingDelichaee, Ab-e-sefid , Alarm & Lar (Kamardasht).Tubifex and Chironomus genus werefound to have the highest frequencies of occurrence in the lake with %77.117 & %21.823respectively followed by Chironomidae and Simulidae from the Diptera order whichaccounted for %72.328 and %13.812 occurrences in four rivers examined in the Study. Thebenthic biomass at various examined Sites and the average wet weight of the benthic biomassin station No one in the lake Was 17.397g and the figure for the examined site in Alarm was20.242 g which were the highest level among Other examination stations the index for theabundance of species in Alarm river was greater than the rest of the examined rivers with12.57. A sum of 354 Pieces of brown trouts was caught in the course of sampling which wereclosely investigated in terms of their digestive tract Content. It was identified that Daphniidaeand Chironomus constituted the bulk of eaten items from the lake with %17.985 and %63.973respectively. Meanwhile, Chironomidae and Simuladae were the most frequently eantenbenthos by the fish with %81.47 and %7.93 respectively.The index for the relative length ofgut was recorded at 0.49± 0.08 which is well indicative of the carnivorous diet of the fish.Theindex for the feeding intensity amounted to 138  83 showing that the one year old fish wereof more feeding intensity.The coefficient of condition (K) was estimated at 1.02  0.142 forall the caught fish. The average wet weight of the benthos was 10.348 g per square meterwhich if extended to 700ha surface area of the lake, the total macrobenthic production in thelake would amount to 72730Kg of wet weight or 6510 Kg of dry weight. Since the SecondaryProduction of macrobenthos have always been double that of their biomass, it is reasonable toassume that the Secondary Production of macrobenthos amount to 145640 Kg by their wetweight and Since the energy transfer in the food chain of the lake from benthos to fish is 10percent, the fish production Capacity Coming from benthic resources of the lake (Lar) would be 14.5 MT, half of which (7000-8000MT) could annually be harvested. Further more, the actual fish Production Capacity might exceed the projected level Since Daphnia, Rotifers and Ostracoda which belong to Zooplanktons, play a part in the natural diet of trout. Meanwhile, rivers Play a major role in fish nutrition and the annual fish production in Delichaee river is about 4481.8Kg while the figures for Ab-e-sefid, Alerm and Lar rivers are 2370.7 4848.7 and 2586.2 Kg respectively, that further increase fish Production in the area and every year half of these resources can be exploitable from the river & the lake.Nevertheless, due to ecological & biological importance of rivers and the probability of environmental Pollution, devastation of natural fish habitats & their nursery grounds, Sport fishing is not recommended at all.

Bibliographic Details

Main Author:	Rajabi Nezhad, Reza
Format:	thesis biblioteca
Language:	Persian
Published:	Islamic Azad University, Science and Research Branch, Tehran, Fisheries 2007
Subjects:	Aquaculture, Biology, Fisheries,
Online Access:	http://hdl.handle.net/1834/34438
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