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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 pike silverside has high aquaculture potential despite its slow growth. In this study, thyroxine (T4) concentrations (0.13, 1.3 and 13 nM), a control with no hormonal supplement and a negative control containing 4.5 mM methimazole (MMI) were tested to evaluate the growth of this species. Juveniles (0.2 g) were exposed by immersion to these treatments for 8 h every second day for120 days, and growth evaluations were performed monthly over the entire trial period. In addition, tissue samples from each treatment group were assayed for triiodothyronine (T3) and deiodinase type 2 (D2) activity. The survival rates in all T4 groups were high, and a signi¢cant increase in growth was observed (average of 58%). The MMI treatment caused an increase in mortality and a reduction in the ¢nal body weight compared with the control. T4 administration did not aiect the tissue levels of T3, and it decreased muscular D2 activity only after 30 days of exposure. These results demonstrated that low concentrations of T4 in the culture environment could improve the growth of this species without affecting tissue hormone levels. The technique may have useful applications for early-stage aquaculture of this and other economically important species.

The tilapia ¢shery in a large Mexican reservoir has declined in recent years, promoting eiorts to enhance stock quality in conjunction with feasibility studies for cage aquaculture. Spatial models to optimize cage location have been developed, incorporating aspects of topography, climate, hydrography, water quality and quantity, land use, infrastructure and socioeconomics. Three cage sizes were modelled, 5, 10 and 15 m diameter, for both high- and low-water levels. When full the, reservoir has a total area of 312 km 2 but a reduction in water level of 13 m was recorded between wet and dry seasons, signi¢cantly reducing the surface area available for cages to 265 km 2 . The results indicate a signi¢cant diierence in the availability of sites between seasons. For the small, medium and large cages at high water level, the areas classi¢ed as highly suitable or suitable were 151, 184 and 146 km 2 , respectively, while at low-water level these areas reduced to 113, 88 and 62 km 2 . Modelling this change in water level and the subsequent loss of available sites provide qualitative and quantitative guidelines for the development of aquaculture sites, their seasonal management and future monitoring, outcomes that can only be achieved using Geographical Information Systems and associated technologies.

Aquaculture continues to be the fastest growing animal production industry and this rate of expansion must continue if aquaculture is to satisfy global demand for fish products in the face of dwindling capture fisheries. The relationship between aquaculture and biodiversity is complex, with examples of positive and negative impacts having been reported. To enable this expansion while avoiding negative impacts from introductions of exotic species, the investigation of indigenous species becomes important and worthwhile.This paper establishes the background to development of new species for culture and describes the example of the Mexican silverside Menidia estor, which has for centuries been the principal species in an artesanal fishery in Lake Patzcuaro, Mexico. The species is geographically isolated and is unique but is now endangered because of a range of factors including overfishing, environmental degradation and introduction of exotic species. Considerable advances have been made recently in developing a closed reproductive cycle, understanding feeding and small-scale on-growing technology for the species. Based on this, a Darwin Initiative programme was developed focused on technology transfer to implement small-scale pilot on-growing thus helping to conserve the species and to improve livelihoods. This has allowed successful pilot scale development of aquaculture for the species while at the same time addressing the objectives of the international Convention on Biodiversity.

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 diierent 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 1 protein and 80 mg kg 1 vitamin C. The upper level of dietary carbohydrate for good growth and survival for juveniles is about 150 g kg 1 . 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 biosynthetize420-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.

Anaesthesia, sedation and transportation of the Atherinopsid, Menidia estor, were investigated using benzocaine, hypothermia and combinations of the two. The optimum dose rates of benzocaine for sedation of juvenile Chirostoma estor were 15 and 18 mg L−1. When hypothermia was used alone, stable sedation of C. estor was induced at 15 and 12°C, with no mortalities and full recovery after about 8 min. There was synergism when benzocaine and hypothermia were combined, with the optimal combination being at 15°C and 12 mg L−1 benzocaine. Successful transportation was conducted over 3.5 and 8.5 h using combined benzocaine and hypothermia. Aloe vera extract used in the transportation medium reduced scale loss. This work has, for the first time, defined a systematically derived system of safe, long distance, live transportation of this species and others of the genus Menidia.

The growth and survival of white fish (Chirostoma estor estor) larvae were measured at different temperatures ranging from 16.1 to 34 °C. A single camera video system was used for accurate measurement of length of larval and juvenile fish, which enabled growth experiments on delicate animals with minimal handling. Use of a length/weight relationship then enabled estimation of mass. When applied to C. estor estor, the error of the system was generally less than 0.5% for length, but increased to over 1% when the distance of the larva to the grids increased. The total practical error in estimation of biomass using the video method was −2.05% for dry weight, with a range from −7.1% to +4.1%. Over a number of experiments, the recorded mortality due to the measuring process was less than 1%, representing a dramatic advance on all previous attempts to work with Chirostoma. This simple method could have wider utility for fragile larvae such as marine fish. Larvae were fed ad libitum with Brachionus rubens rotifers and Artemia franciscana nauplii for 1 month. The results showed that the optimum temperature for specific growth rates (SGR) was 28 °C, although survival was only 18% at this temperature. The best survival (53%) was at temperatures of 22 and 25 °C. The best overall temperature for growth and survival was 25 °C.

The growth and survival of Penaeus vannamei postlarvae was measured at temperatures of 20, 25, 30 and 35 °C and salinities of 20, 30, 35, 40 and 50%.. Groups of 30 animals were used in each combination of conditions, in triplicate. The results clearly show that juveniles of this species have their best survival between temperatures of 20 and 30 °C and salinities above 20%.. Best growth was obtained between temperatures of 25 and 35 °C, with little difference being noted among salinities. Survival and growth coincide best at around 28 to 30 °C and 33 to 40%.. Calculated overall production was shown to be best in these conditions. The results demonstrate a high coincidence between the experimentally determined optimum conditions for production and the prevailing conditions in the coastal environment from which the animals originated.

In experiments designed to demonstrate the effects of instantaneous changes in salinity, juveniles were able to resist abrupt changes from fresh water up to 15‰ salinity without mortality, and the median lethal salinity (MLS) was 24‰. In a growth trial of 12 weeks duration at salinities of 0, 5, 10, 20, 30 and 35‰, final body weight, weight gain, specific growth rate, food intake and food conversion ratios were always higher in saline environments than in fresh water although differences were not significant. The best growth was observed at 10 and 20‰, the optimum probably being between these concentrations. The fish is clearly euryhaline.

The morphometric relationships, standard length-weight, standard length-width and weight-width for Cichlasoma urophthalmus (Gunther) in the weight range 0.78-262g were: log10 weight =−4.35 + 2.95 × (log10 standard length); log10 width =−0.73 + 0 99 × (log10 Standard length) and log10 width = 0.74 + 0.33 × (log10, weight). Two box graders were designed and tested based on these data. The operation efficiency (expressed as a percentage of the sample used to test it) was 96.1 % and 95% for the two graders. Results indicated a tendency to undergrading (small fish detained by the bars) by the first grader and overgrading (large fish going between the bars) by the second, the latter as a result of the major variability in the body shape from fish as they grow. The results are satisfactory, and larger graders for commercial use could be constructed based on these relationships.

The feeding habits of the cichlid Cichlasoma urophthalmus were studied in a brackish-water lagoon in Yucatan Peninsula, Mexico, from spring 1985 to spring 1986. The strong mandibular, maxillary and pharyngeal teeth, and the short intestine strongly suggest that C. urophthalmus is primarily a carnivore. Subsequent gut contents analysis revealed that this species feeds principally on invertebrates throughout the year and that there were few differences between the five seasons studied. The algal material found in some stomachs may be consumed as a consequence of predation on small invertebrates, but the feeding structures and short intestine makes this species unable to digest vegetable materials efficiently. Differences with other cichlids used in aquaculture are discussed.