Rabbitfish: A Herbivorous Marine Fish

November | December 2009 Feature title: Rabbitfish - A herbivorous marine fish International Aquafeed is published five times a year by Perendale Publishers Ltd of the United Kingdom. All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2009 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058

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rabbitfish

rabbitfish

sizes found, habitats occupied and natural foods grazed. In my lab, we determined optimal salinity and various salinity tolerances, temperature, stocking density, growth rates in Long-term without fishmeal sea water and in inland For the past four years, we have been low salinity well water, studying the environmental tolerances of intra-specific competition, such a specie Siganus rivulatus at the marine reaction to water movelab of the American University of Beirut. ment and tolerances to We are very optimistic about this species ammonia and nitrite. and believe it is an excellent candidate for Presently, research is aquaculture. on nutrition. Presently, rabbitfish in captivity are mainPreliminary studies on tained on teleost feeds rich in fishmeal. nutritional requirements Some trials on protein requirement for of the marbled spinefoot S. guttatus found that a diet with 35 percent Aquaculture research lab at the American University of Beirut. rabbitfish Siganus rivulaprotein was optimal. tus, suggest that optimal However, these experiments were not dietary protein for the replicated for other siganid species and fish is 35 percent inclusion in the diet. not even evaluated for the same species in diet with rape seed oil had a greater However, this conclusion was obtained various environments. The diets tested also proportion of 18-carbon omega-3 FA in using a formula that estimates best use contained a 10 percent fishmeal inclusion. their flesh. of feed from determinations of protein We still do not know if diets without Further reseach efficiency and feed efficiency. In our first fishmeal are suitable. We also do not know Future research on the fish will be to experiment, fish offered feed with graded if the fish can be reared long-term on diets better determine protein and lipid requirelevels of protein inclusion between 25 without fish oil inclusions. ment, protein to energy ratio in their diets, percent and 45 percent did not show difpossibilities of fishmeal replacement in their ferences in survival or growth. Two-pronged research diets and the possibility of using algal prodThe experiment is being repeated. At the American University of Beirut, ucts to develop a sustainable aquaculture A lipid requirement experiment that was we have been studying siganid biology and industry. performed recently indicates that the optiaquaculture for six years. The research has We are also developing collaborative mal dietary lipid inclusion for S. rivulatus is been two-pronged, with Dr Michel Bariche work with the laboratory of Professor between eight percent and 10 percent of studying the ecology of the fish in its natuSimon Davies at The University of Plymouth the feed by weight. We also performed an ral environment and my lab studying the to study effects of various dietary ingreexperiment where fish oil was replaced by environmental physiology and aquaculture dients on gut microbiota and non-specific various other oils including corn oil, soy oil requirements of the fish. immune response variations with variation and rape seed oil. Dr Bariche’s group have defined spawnin diets. Growth over an eight-week period ing seasons, age of metamorphosis and of We strongly believe that there is a future was not affected by any of the oils used maturation in the wild as well as maximum for rabbitfish aquaculture if we develop but fatty acid necessary production protocols and diets composition as well as expertise before we start encourof the filet aging farmers to try rearing it.The market is was affected. already available. Fish offered The science is getting there! the diet with fish oil had a s i g n i f i c a n t ly greater proMore inforMation: portion of Imad Patrick Saoud EPA and DHA Aquaculture and Aquatic Science Dept of Biology omega-3 fatty American University of Beirut, Bliss St acids in their Beirut, Lebanon flesh than all Tel: +961 1 350000 ext 3913 other fish. Website: http://staff.aub.edu.lb/~is08/ F i s h American University of Beirut Campus. offered the alternate sources of protein for fish diets. If growth of the aquaculture industry is to be sustained, then techniques to rear novel species of marine fishes that do not necessarily need fishmeal in their diets have to be developed.

Rabbitfish: by Imad Patrick Saoud, Aquaculture and Aquatic Science, American University of Beirut

A herbivorous marine fish

Global production of fishmeal is not increasing, but demand for marine fish is. Therefore, we had better start developing the technology to culture a marine herbivore!

S

iganids are herbivorous and can potentially be grown using diets without fishmeal supplementation.

They are a relatively small family of herbivorous fishes with important commercial value widely distributed in the Indo-West Pacific Region. They migrated to the Eastern Mediterranean through the Suez Canal and have now established viable populations in their new habitat. They are relatively easy to rear and are thus considered suitable for aquaculture. They are hardy and easy to maintain in tanks and ponds. Moreover, they are extremely euryhaline which makes them an excellent candidate for rearing in many locations not suitable for other species. Various species are aquaculture candidates in the Philippines and other South-East Asian countries as well as Egypt, Cyprus, Lebanon,Turkey and India.

Excellent market Siganids have an excellent market in the Middle East and south East Asia, and to the ethnic Chinese, rabbitfish symbolize good fortune. Aquaculture of marine fishes is not always done in optimal environments. In many regions of the world, estuarine salinities could become very low during the rainy season, very high during the dry sea-

son or vary daily with tidal currents. Fishes being reared in these environments need to be able to tolerate salinity extremes and diurnal salinity variations. Research in our lab shows that one such species is the rabbitfish Siganus rivulatus. The fish survive and grow well in salinities between 10 and 50ppt and are quite eurythermal (17oC to 32oC; optimal 27oC). Their tolerances to Ammonia and Nitrite are very high (> 3mg/l) for typical marine species, and they are suitable for culture in most marine environments.

Fishmeal unsustainable

Wild rabbitfish in South Africa (www.spearfishingsa.co.za)

20 | InternatIonal AquAFeed | november-December 09

Another factor related to the rapidly expanding field of marine fish farming is that use of fishmeal is nearing unsustainable levels. Fishmeal production has been nearly constant, averaging about six million tonnes annually and demand for fishmeal is growing, putting pressure on fishery stocks and causing fish meal prices to increase. It is therefore necessary to find

november-December 09 | InternatIonal AquAFeed | 21

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Rabbitfish: - A herbivorous marine fish

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