Effect of the initial stocking body weight on growth of spotted rose snapper Lutjanus guttatus (Steindachner, 1869) in marine floating cagesEfecto del peso inicial de cultivo sobre el crecimiento del pargo lunarejo Lutjanus guttatus (Steindachner, 1869) en jaulas flotantes marinas

ABSTRACT. Diploid and triploid Crassostrea gigas oysters were cultivated at three farms (Guasave, Navolato and Ahome) in Sinaloa, Mexico, to evaluate their growth and economic performances. Growth rate and survival of oysters were compared in long-line cultivation and were mostly affected by water parameters rather than ploidy or their interaction. The highest growth rates for shell length (8.01 mm month ) were obtained for the Ahome/triploid group. Survival differed significantly from 98.6% for the Guasave/triploids to 76.7% for the Ahome/diploids. After the first production cycle, more than 80% of production costs represent the purchase of cultivation equipment and salaries contributed with around 9%. The Guasave farm produced the highest profits (US$8,053.71 diploids, US$8,182.19 triploids). Use of diploids starting the production cycle on October-November to avoid mortality and improve final profit is recommended.

The main purpose of this study was to review the growth models used in fish culture and demonstrate the benefit of using the most appropriate growth model for aquaculture studies. For this reason, another part of this study was to use a dataset from spotted rose snapper (Lutjanus guttatus Steindachner, 1869) cultured in floating cages to determine what growth models were applicable to this species. A total of 558 weight‐at‐age data points from a commercial farm located near Nayarit, Mexico were used. The fish were cultured for 270 days in three cages of 125 m3 capacity. The initial density was 25 fish m−3, with an average weight of 2.07 ± 0.52 g. Four asymptotic models (von Bertalanffy growth model, a logistic model, the Gompertz growth model and the Ratkowsky modified model), three nonasymptotic models (exponential, power extended and persistence models) and three versions of the generalized Schnute model were selected as candidate models. The best model was selected based on the Akaike information criterion. The maximum log‐likelihood algorithm was used to parameterize the models considering a multiplicative error structure. The survival was 90%, and the average final weight was 429.84 ± 31.53 g. We concluded that the best model for describing the growth of spotted rose snapper farmed in marine floating cages was the Schnute model.

We present results of a long-term study aimed to optimize Nile tilapia O. niloticus production in a recirculating aquaculture system (RAS) in México City. Three experiments were evaluated: 1) fry production; 2) production of masculinized fries; and 3) assessment of growth under three different densities (10, 30 and 75 fish/m 3). The broodstock produced on average 2400 ± 600 fry every 15 days during six months, with a total production of 28,800 ± 2000. One hundred percent males were produced in 274-L raceways in an eight-week period. The obtained results in fish production in the RAS system indicated variations related to density. A daily growth rate of 3.6 g/day was registered with a density of 10 fish/m 3 , 0.9 g/day in 30 fish/m 3 and 0.4 g/day in 75 fish/m 3. This information could be useful for production purposes in this type of systems.

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This study undertakes the characterization of digestive proteases in the juvenile green cichlid, Cichlasoma beani. The results obtained showed a higher activity of alkaline proteases (0.14 ± 0.01 U mg protein −1 ) compared to acid proteases (0.07 ± 0.01 U mg protein −1 ) in this species. The optimum temperature of the alkaline proteases was 65 • C and these enzymes were more thermostable to temperature changes than the acid proteases, characterized by an optimal temperature of 55 • C. The pH optimum was 2 for acid proteases, and 11 for alkaline proteases, which were also more stable to changes in pH between 8 and 10. The use of specific inhibitors showed an acid protease inhibition of 88% with pepstatin A as inhibitor. In the zymogram SDS-PAGE analysis of alkaline proteases, five active fractions were revealed, indicating the presence of serine proteases. These results confirm that both alkaline and acid proteases are involved in the digestion of C. beani, and suggest that this species is omnivorous with carnivorous tendencies. The present study contributes to our knowledge about the digestive physiology of C. beani, and can be applied towards improved understanding of the kinds of protein sources that could be used in the development of inerts diets.

The super-intensive white shrimp system is more productive (t ha−1) than traditional systems. However, it implies greater investment in infrastructure and machinery, a continuous supply of electricity, and a specialized workforce. Therefore, the sustainability of a shrimp farm model operating in a super-intensive system in Nayarit (Mexico) was evaluated using financial analysis and life cycle assessment. The investment is important, but the fixed costs (16%) are much lower than variable costs (84%). The super-intensive farm is economically viable, with an overall profitability (29%) that is higher than that of other agri-food activities in Mexico. It is also an activity that generates a lot of employment, in relative terms, as well as economic movement in the area. The potential environmental impacts are higher than those registered in semi-intensive shrimp systems but slightly lower than those registered in intensive systems. The estimated global warming value per kg of shrimp is 5.08 kg CO2-eq, an intermediate value. Also, as the shrimp production is much higher than in traditional systems, it could have a great and positive impact on the maintenance and regeneration of the mangrove ecosystem.

Growth, immunological and physiological parameters of white shrimp Litopenaeus vannamei reared at different salinity levels (1, 10, 15, 25 and 35 g/L) at stocking density of 214 shrimp/m 3 were examined at 1, 30 and 63 days. Results showed that the total haemocyte count (THC) of shrimp decreased with time at all salinity levels, indicating a potential reduction in the resistance of shrimp against pathogens, since a low value of THC indicates a perturbation of the immune system. Glucose and protein values observed in the haemolymph throughout the study indicate that shrimp adapted well to low salinities (1, 10 and 15 g/L). Although of those shrimp reared at 10 g/L only 83.3% survived, at this salinity, shrimp depicted a higher glucose concentration in haemolymph at the beginning and end of the study. K E Y W O R D Simmune and physiological response, Litopenaeus vannamei, salinity