The use of green algae ulva meal (UM) (Ulva rigida) was evaluated as a replacement for soybean meal in a practical diet formulated to contain 28% crude protein, 7.50% lipid and 15 kJ gross energy g )1 . Soybean meal was replaced by 0%, 10%, 20% and 30% of UM (diets U 0 , U 1 , U 2 and U 3 , respectively). The feeding experiment was carried out in an open circulation system. Each diet treatment was applied to triplicate groups of 30 fish (21.37 ± 0.193 g average wet weight) per tank (400 L) arranged in a completely randomized design. The fish were hand fed to satiation four times daily between 07.00 and 18.00 hours for 75 days. There were no significant differences (P > 0.05) in growth performance among fish fed with diets U 0 , U 1 and U 2 . However, fish fed diet U 3 had significantly lower growth (P < 0.05) than those fed diets U 0 , U 1 and U 2 . Fish fed the control diet (U 0 ) and diets including 10% and 20% UM had significantly (P < 0.05) better daily weight gain, relative growth weight, specific growth weight and protein efficiencies ratio than those fed with diet U 3 . Feed conversion ratio increased with increasing UM content, but only the value found in fish fed with diet U 3 differed significantly (P < 0.05) from all other treatments. Survival rates ranged between 91.11% and 93.33%. No feedrelated mortality was observed during the entire experimental period. Apparent protein digestibility (APD) of diets ranged from 87.06 to 69.91% and was lowest for fish fed with diet U 3 . In general, APD values decreased with increasing inclusion levels of UM, explained by the increase of anti-nutritional factors and high non-digestible fibre content. Compared to the control diet (U 0 ), fish fed diets containing high levels of UM had lower levels of carcass lipid and higher levels of carcass moisture. Results show that this product can be included by up to 20% in practical male Nile tilapia diets with no detrimental effects.

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The potential of waste date meal (WDM; low‐quality date palm, Phoenix dactylifera L.) as a carbohydrate source in formulated diets for Nile tilapia was evaluated. Four isocaloric‐practical diets (15.7 kJ g−1) were formulated incorporating WDM at 0, 100, 200 and 300 g kg−1 levels as partial substitutes for soybean meal (SBM). These were designated D0 [284 g crude protein (CP) and 383 g carbohydrate (CHO) kg−1 diet], D1 (279 g CP and 446 g CHO kg−1 diet), D2 (207 g CP and 495 g CHO kg−1 diet) and D3 (175 g CP and 578 g CHO kg−1 diet). Each diet was fed to three replicate groups of 30 fish [20.20 ± 0.09 g (±SE)] for 75 days. No feed‐related mortality was observed during the entire experimental period. Final body weight (FBW) and specific growth rate (SGR) in the different treatments were statistically not significantly different (P > 0.05). Protein efficiency rate (PER) was lowest in diet D0 and increased with decrease of SBM content (D1–D3). A significant increase in whole body lipid content was recorded in fish fed diets D2 and D3. Results showed that WDM could be a substitute for SBM up to 300 g kg−1 in practical Nile tilapia diets without compromising growth.

phycoerythrin is considered to be a predominant pigment in red algae. This pigment is at present used in food industry as colorant. Nevertheless, because of the spectral properties, it is used mainly in clinical and immunological analysis (Mensi et al.2012), in fluorescence microscopy and flux cytometry (Glazer and Stryer 1984;Kronick 1986). It is also reported that R-phycoerythrin and phycocyanin act as a part of protective mechanism in seaweeds in general (Sinha et al.1995) and in Gracilaria caudata particularly (Araujo et al.2014). To our best knowledge, few studies (Molloy and Bolton 1996;Mensi et al. 2009) were published regarding the effect of both depth and initial fragment weights on growth and proximate chemical composition of Gracilaria gracilis (previously known as G. verrucosa).Presently, there are neither large scale seaweed cultivation nor agar industry in Tunisia.Nevertheless, several attempts of Gracilaria farming were performed in the two last decades, using both spores (Ben Said and Aouini 2014) and cuttings/fragments (Ksouri et al.1999(Ksouri et al. , 2000 Mensi et al.2009). Four farming methods were used: ropes, sand filled plastic tubes, spade and suspended system in hoop-nets. On the other hand, some experimental agar extractions have been carried out on Gracilaria gracilis (Ben Said and Ksouri 1999; Ben Said et al.2015).This study aimed to determine the ability of Gracilaria gracilis to be cultivated at two different water depths in Bizerte lagoon, using net pockets. Additionally, relatively low initial fragment weights, compared with previously reported studies (Ksouri et al.1999(Ksouri et al. , 2000 Mensi et al.2009) were also tested in order to have an appreciable biomass with a high daily growth rate (DGR) in relation to environmental factors. The biomass could be firstly used for agar extraction and secondly for other potentially interesting compounds. Hence, agar yield, gel strength, gelling and melting temperatures were investigated because of their properties to

The aim of this research is to statistically optimize enzymatic hydrolysis parameters for the production of R-phycoerythrin (RPE) from red algae Gracilaria verrucosa. Six independent variables, incubation temperature, incubation time, ratio of buffer to raw material, cellulase loading, xylanase loading, and pH, were selected for response surface methodology studies. A central composite design was employed to maximize RPE production. A mathematical model with high determination coefficient (R 2 = 0.86) was developed and could be employed to optimize RPE extraction. The optimal extraction conditions of RPE were determined as follows: incubation temperature (48°C), incubation time (6 h), ratio of buffer to raw material (20 w/v), cellulase loading (15%), xylanase loading (5%), and pH (6.5). Under this optimal condition, the experimental yield of RPE was 6.25 mg g −1 .Based on the result of response surface methodology and desirability function approach study, total sugar, the main by-product in RPE extraction was considered as another response. A new optimal condition was predicted as follows: incubation temperature (30°C), incubation time (12 h), ratio of buffer to raw material (20, w/v), cellulase loading (15%), xylanase loading (5%), and pH (6). Under this condition, similar RPE levels were obtained while the concentration of total sugar decreased by 40%.