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A study was conducted in order to determine the protein requirements of juvenile Mexican silverside (Menidia estor). Seven isoenergetic diets (≈19.9 MJ kg−1) with dietary protein levels of 250, 300, 350, 400, 450, 500 and 550 g kg−1 were prepared as flakes using jack (Caranx sp.) and red snapper (Lutjanus sp.) fillets, tuna (Thunnus sp.) ovaries and California squid (Loligo sp.) as protein sources, and their effects on growth, survival and feed utilization of juvenile M. estor (69.24 ± 5.03 mg initial weight) were evaluated. Fish were fed by hand to apparent satiation, five times a day, for 8 weeks. Best growth and survival were obtained with diets with protein levels between 400 and 500 g kg−1, with no significant differences between them (P > 0.05). Specific growth rate and feed intake were also highest for these treatments (P < 0.05). There were no significant differences in feed conversion ratio and protein efficiency ratio between fish fed all the diets. Broken‐line analysis of individual weight gain against protein level showed a protein requirement of 409 g kg−1 for juveniles of M. estor.

A 7-week feeding trial was conducted to investigate the effects of replacing fish meal by autoclaved Salicornia bigelovii seed meal (SSM), supplemented with varying cholesterol levels, on feed intake, growth performance, body composition and survival of Nile tilapia Oreochromis niloticus fingerlings under laboratory conditions. SSM was tested at different inclusion levels (0, 25, 50 and 65 % of total protein), using different levels of cholesterol supplementation (0, 1, 2 and 2.6 %) in isonitrogenous (420 g Kg-1 DM crude protein) and isocaloric (18.52 MJ Kg-1 DM) fish meal-Soybean meal-based diets. Triplicate groups of fish (374 ± 15 mg, initial fresh body weight) were randomly stocked in 18 20-L plastic tanks at a stocking density of 20 fish per tank and were fed to satiation by hand five times a day, 7 days per week. Feed intake, growth performance and survival were significantly affected by the SSM inclusion level and the cholesterol supplementation. The lower growth performance of fish fed diets containing SSM without cholesterol is thought to result from the presence of saponins in the meal. When cholesterol is added, the saponin-induced toxicity is ameliorated, which is evident from growth and survival responses, up to 50 % of SSM protein inclusion. At the highest level of SSM inclusion (65 %), growth and survival were very poor, despite the addition of cholesterol. The results of the present work suggest that autoclaved SSM can partially substitute fish protein in diets for O. niloticus fingerlings at levels up to 50 % of the dietary protein if 2 % cholesterol is added in fish meal-SBM-based diets

The Mexican silverside, Menidia estor, is a species with great regional importance and with very high prices in local markets. Unfortunately, due to high ¢sheries pressure, environmental degradation and pollution, the species has become endangered. Recently, there has been much progress in the biotechnology of this species, aimed at its culture, and the present paper describes the advances in feeding and nutrition of those important ¢sh. M. estor is a stomachless, zooplantophagous ¢sh, which also occasionally feeds on small ¢sh and crustaceans in the adult stage. Studies on the digestive enzymatic activities show high proteolytic capacity and a late or di¡erent model of digestive maturation from that described for marine stomach ¢sh. Nutritional studies on M. estor have shown that juveniles have dietary requirements of about 400 g kg À1 protein and 80 mg kg À1 vitamin C. The upper level of dietary carbohydrate for good growth and survival for juveniles is about 150 g kg À1 . Based on the high docosahexaenoic acid (DHA) content in £esh when fed on diets low in DHA, it is believed that the species has the capacity to biosynthetize 420-carbon fatty acids from 18-carbon fatty acids. The high levels of DHA in £esh makes this ¢sh a very signi¢cant potential component of human nutrition. Using these ¢ndings the ¢rst practical diets for commercial culture of the species have been developed.Keywords: Menidia estor, nutritional requirements, culture Recently, much e¡ort has been invested in development of the culture of this species and current advances in the biology and culture of M. estor were summarized by Mart|¤ nez-Palacios, Morte,