The use of prebiotics and probiotics as feed supplements that improve efficiency of intestinal bacteria is becoming de rigueur in animal husbandry in many regions worldwide. We tested the effects of a commercial probiotic (Biogen Ò ) containing allicin, high unit hydrolytic enzyme, Bacillus subtilis spores and ginseng extracts on survival, growth, carcass composition and feed cost/benefit in rabbitfish Siganus rivulatus. Fifteen net cages (100 · 100 · 40 cm; L · W · H) were stocked with 10 juvenile rabbitfish (10.3 g per fish) each and placed in a large rectangular tank and offered feed at 4% body weight daily. Cages were offered one of five isonitrogenous and isocaloric diets containing 0, 1, 2, 3 and 4 g kg )1 probiotic at three replicates per treatment for 98 days. Fish in all cages were weighed at 2-week intervals and feed regimen was adjusted accordingly. Rabbitfish offered the control diet exhibited lower growth and feed utilization than all experimental treatments. There was no effect of probiotic inclusion level on survival but growth was better at all inclusion levels than in the control. No significant differences (P > 0.05) in growth were observed among fish groups fed various levels of the probiotic. Carcass composition was not affected by dietary probiotic inclusion. Ultimately, when all variables are considered, Biogen Ò inclusion to diets appears to reduce feed cost per unit growth of rabbitfish. KEY WORDS

Rabbit¢sh are an Indo-Paci¢c herbivorous marine ¢sh that have good market demand and are suitable for aquaculture. The present work was performed to determine dietary protein inclusion necessary for optimal growth of juvenile rabbit¢sh Siganus rivulatus. Six diets with increasing levels of protein (10, 20, 30, 40, 50 and 60 g crude protein 100 g À 1 feed) and similar levels of gross energy (20 MJ kg À 1 ) were prepared and o¡ered to S. rivulatus juveniles maintained in triplicate cages placed in two large water tanks for 49 days. Growth progressively improved with dietary protein for ¢sh o¡ered diets from 10% to 40% protein inclusion. Diets with greater protein levels did not improve ¢sh growth beyond that observed in the 40% group. Daily feed intake, apparent protein utilization and feed conversion ratio decreased as dietary protein increased. Protein e⁄ciency (PE) was greatest (1.47) in ¢sh o¡ered the 10% protein diet and least in ¢sh o¡ered the 60% protein diet (0.80). No di¡erences in PE were observed among all other treatments (20^50%). Results of the present work suggest that minimum dietary requirement for suitable growth of S. rivulatus juveniles is 40% protein when digestible energy of the diet is 16^18 MJ kg À 1 .

A 60-day feeding study was performed to evaluate the role of dietary commercial wood charcoal (CWC) in fish growth performance, body composition and water quality of fingerlings red tilapias (Oreochromis mossambicus 9 Oreochromis niloticus). Four levels of charcoal (10, 20, 30 and 40 g kg À1 ) were added to the control diet (0 g kg À1 CWC) and fed to red tilapias (initial weight of 1.20 AE 0.04 g). At the end of the feeding trial, the fish weight gain, specific growth rate, feed conversion ratio, protein efficiency ratio and energy retention of the fish groups fed 30 and 40 g kg À1 (CWC) in diet were significantly (P < 0.05) higher comparing with all other tested fish groups. Moreover, some proximate composition such as crude protein and nitrogen retention efficiency g kg À1 of the fish groups fed on 30 and 40 g kg À1 CWC diets showed higher values (P < 0.05) than those of other tested fish groups (0, 10 and 20 g kg À1 CWC). Apparent digestibility coefficients of protein and dry matter were improved (P < 0.05) in CWC-tested fish groups compared to the control fish group. These data were powered by the data of the water quality that showed significant (P < 0.05) enhancement in both dissolved oxygen and ammonia concentrations by the increment in dietary charcoal levels. The above-mentioned parameters' data suggested that 30 g kg À1 dietary CWC can be considered as a suitable level to maintain normal growth of red tilapia juveniles as well as to enhance water quality of the rearing area.

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Marbled spinefoot rabbitfish, Siganus rivulatus, is an herbivorous euryhaline marine fish with established market demand. Interest in aquaculture of the marbled spinefoot is increasing in Eastern Mediterranean, Red Sea, and Arabian Gulf nations. However, culture protocols for commercial production are incomplete. In this work, we evaluated the benefits of size sorting S. rivulatus juveniles before stocking. Two experiments were performed. In the first experiment, juveniles were size sorted into three different groups: small (5.5 g), medium (8.7 g), and large (12.1 g), and 15 fish were stocked per tank in a recirculating system of 180‐L tanks with three replicates per treatment. Two additional treatments were established: a mixed treatment consisting of five fish from each size category stocked together and a small treatment offered as much feed daily as the medium treatment. Feed was offered at 4% body weight daily for 8 wk. Survival was greater than 95% in all treatments. Average final weights of the fish at harvest were 52.2, 38.1, 28.3, 39.6, and 30.5 g for large, medium, small, mixed, and small with high‐ratio treatments, respectively. Fish in the large treatments grew faster than fish in all other treatments. In the second experiment, fish were trapped off the Beirut beach in April, June, and August 2007. Individual weight and length and condition index of each fish were determined. Males and females were differentiated by identifying testicular and ovarian tissue, respectively. Gender identification was performed at 10× magnification. There were no differences in length and weight between males and females in all three samples collected. Results suggest that size grading of juvenile rabbitfish will maximize culture production by selecting faster growing fish with better condition indices but will not select for gender because S. rivulatus juveniles (10.6–12.1 cm) do not exhibit sexual size dimorphism.

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