INTERNATIONAL JOURNAL OF AGRICULTURE & BIOLOGY ISSN Print: 1560–8530; ISSN Online: 1814–9596 08–180/AWB/2008/10–5–561–565 http://www.fspublishers.org Full Length Article To cite this paper: Hayat, S. and M. Javed, 2008. Regression studies of planktonic productivity and fish yields with reference to physico-chemical parameters of the ponds stocked with sub-lethal metal stressed fish. Int. J. Agri. Biol., 10: 561–5 Regression Studies of Planktonic Productivity and Fish Yields with Reference to Physico-chemical Parameters of the Ponds Stocked with Sub-Lethal Metal Stressed Fish S. HAYAT 1 AND M. JAVED Department of Zoology and Fisheries, University of Agriculture, Faisalabad-38040, Pakistan 1 Corresponding author’s e-mail: sikanderhj@yahoo.com ABSTRACT Three major carps viz. Catla catla, Labeo rohita and Cirrhina mrigala at fingerling stage were exposed to none and sub-lethal concentrations of individual metals (Fe, Zn, Pb, Ni, Mn) and their mixture in glass aquaria for 90 days. After stress period three fish species were grouped metal/treatment wise and stocked, separately in earthen ponds and reared for one year under semi-intensive culture system. All the physico-chemical variables, except water temperature, showed significant variations among ponds stocked with control and metal stressed fish. However, season exerted significant effect on the characteristics of pond’s water. In all the ponds, except that stocked with Ni stressed fish, dissolved oxygen showed direct relationship with planktonic productivity of water. Temperature exerted significant effect on planktonic productivity of the ponds stocked with Fe and Mn stressed fish. Results revealed significant contribution of total alkalinity on the planktonic productivity also. The correlation coefficient between alkalinity of water and planktonic productivity was positive. Step-wise regression computed for each pond revealed K to be a sole water quality variable that exerted substantial influence on fish yield in all the ponds except those of control fish. In all ponds, except those stocked with Zn and Ni stressed fish, total alkalinity showed negative relationship with fish yield. Under all the treatments, fish yield showed direct dependence on the existing planktonic productivity indices of ponds except those stocked with Zn and Ni stressed fish. The regression coefficients of variables in the regression model computed for all the ponds were non-significant except the pond stocked with metal mixture stressed fish. It is concluded that exposure of major carps, at fingerling stage, to sub-lethal levels of different metals have resulted variable fish yields under semi-intensive culture depending upon the planktonic productivity and physico-chemical parameters of ponds. Key Words: Major carps; Sub-lethal metal stress; Fish yield; Growth INTRODUCTION There are several causes of pollutant discharges into the rivers of Pakistan. Swift increase in population, spontaneous urbanization and founding of industries are few to name. The environmentalists have already raised apprehensions about the detrimental effects of un-treated wastewater discharge on the aquatic ecosystems of the rivers (Javed & Hayat, 1999). It is because the presence of heavy metals such as Fe, Zn, Pb, Ni and Mn beyond the permissible limits in the untreated wastewater have adversely affected the indigenous fish fauna especially the major carps (Javed & Mahmood, 2001). Though these trace elements promote physiological processes yet their too high concentration have toxic effects on the aquatic life (Javed, 2003). Catla catla, Labeo rohita and Cirrhina mrigala are the most successful species of polyculture in Pakistan due to suitable climate for their culture on one hand and their consumer liking on the other. Therefore, the polyculture of these major carps has assumed much popularity among the private as well as the public sector farms in the recent past. Nevertheless, the density of major carps in natural waters has alarmingly been declined due to un-treated sewage and industrial discharges into the rivers bearing higher concentrations of heavy metal contaminants. Ultimately, the fish production of Pakistani inland waters has reduced due to population depletion and decline in growth potential of these three indigenous fish species (Javed, 2004). In addition, the natural spawning grounds of major carps have also been adversely affected. Fish seed collected from polluted sites of the rivers has been found to deliver stunted and variable growth. Under the scenario, the farmers are un-able to obtain higher fish yield that exercises negative effect on their socio-economic conditions. This necessitated planning a research project to investigate the effects of sub-lethal heavy metals toxicity on the yield potential of major carps depending upon the planktonic productivity and physico-chemical parameters of pond water under semi-intensive polyculture system being practiced in Pakistan at large scale.