Nitrogenous Excretion of Penaeus monodon Postlarvae Fed with Dierent Diets F. SHISHEHCHIAN , F. M. YUSOFF , H. OMAR and M. S. KAMARUDINà  Department of Biology, University Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia àDepartment of Agronomy and Horticulture, University Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia This study is designed to determine ammonia and nitrite excretion by Penaeus monodon 25±30 day old postlarvae fed with dierent diets (arti®cial and natural). Shrimps were fed with Chaetoceros calcitrans (phytoplankton), chironomid larvae (benthos), Brachionus sp. (rotifer) and arti®cial diet. In the control treatment, shrimps were not fed. The highest concentration of ammonia was excreted by shrimps fed with arti®cial diet and the lowest by that of control treatment. All treatments except where shrimps fed on C. calcitrans showed a sudden increase in ammo- nia-N excretion after 36 h. C. calcitrans contributed to high ammonia excretion only after 61 h. Shrimps fed with Brachionus sp. (rotifer) showed signi®cantly higher nitrite excretion rate compared to other treatments. Shrimps fed on C. calcitrans depicted the lowest nitrite excretion. This experiment indicated that nitrogenous excretion was pre- dominant in shrimps fed with arti®cial diets. Live food like algae and chironomids, despite a high protein content, contribute to low nitrogenous excretion and hence pose less adverse eects on water quality compared to arti®cial diets. Ó 1999 Elsevier Science Ltd. All rights reserved. Keywords: Penaeus monodon; excretion; ammonia; ni- trite; natural food; arti®cial diet. Introduction Intensive shrimp farming is becoming a common activ- ity in many tropical and sub-tropical countries. One of the major impacts of this industry is the eutrophication of coastal waters due to untreated discharge from shrimp ponds. Although shrimp farming is a relatively benign activity compared with other types of agricul- tural, industrial and residential development, it may adversely aect coastal environments, especially, where the regulatory framework is weak or inappropriate and shrimp farm development is intense. To minimize the environmental impact of aquaculture euents on coastal waters, it is necessary to know the source of the nutrients and ways to reduce their con- centrations. Although the type of wastes produced in aquaculture farms are basically similar, there are dif- ferences in quality and quantity of the euents de- pending on the species cultured and the culture practices adopted. The production of faecal and excretory wastes obviously depends on the stocking density, feed type and feeding management in the farm. The feed man- agement in terms of feed type, amount and frequency is important to ensure that the water quality of the pond is not adversely aected, which may in turn aect the health and production of the cultured organisms. Crustaceans are generally considered to be ammoniotelic, mainly converting the end products of nitrogenous catabolism to ammonia. Nitrogen is mainly excreted as ammonia (60±70%), with small amounts of amino acid, urea and uric acid (Chen and Kou, 1996a,b). In crustaceans, the possible mechanism of ammonia excretion is passive NH 3 and NH  4 euxes and ion exchange of NH  4 for Na  (Pequeux and Gilles, 1981). Toxic nitrogenous compounds have been reported to decrease the growth and to some extent cause mortality of cultured shrimps (Wickins, 1976; Mevel and Cham- roux, 1981). In shrimp ponds, decomposition of organic matter also contributes to the accumulation of inorganic nitrogen such as ammonia, nitrate and nitrite. Thus, it is important to estimate the concentration of the toxic forms of nitrogen from dierent sources. So far, no further studies on the nitrogenous excretion rate of P. monodon in response to dierent diets have been reported. Accordingly, this study was conducted to determine the ammonia and nitrite excretion of P. monodon postlarvae fed with arti®cial and live food diets. Materials and Methods The experiment was done in triplicate using plastic aquaria (about 15 ´ 8 ´ 8 cm) ®lled with 500 ml aerated, ®ltered and autoclaved seawater maintaining salinity of 20±25 ppt. Shrimps were fed (ad libitum) with equal PII: S0025-326X(99)00082-X Marine Pollution Bulletin Vol. 39, Nos. 1±12, pp. 224±227, 1999 Ó 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/99 $ - see front matter 224