A 11-week feeding trial was carried out to determine the effects of the probiotic bacteria Lactobacillus casei from the commercial product Yakult Ò on the growth performance, proximal composition, protein content of skin mucus and stress resistance of juvenile Porthole livebearer Poeciliopsis gracilis. Triplicate groups of 15 juveniles per tank with an initial weight of 47 ± 9 mg (mean ± standard deviation) were fed with Artemia nauplii enriched with the probiotic, by using the bacteria cells plus the fermented milk (group ProN) and the other (group ProC) by using only the bacterial cells, eliminating the fermented milk by centrifugation. A control of fish was set up, by feeding non-enriched Artemia nauplii. Growth performance and survival rates did not show significantly differences among the treatments and control group, but a slightly tendency of higher values for body weight, weight gain and specific growth rate was observed in the juveniles of ProC treatment. Whole body proximate composition did not show significant differences among the groups, but higher values of protein and lipid contents were observed in the groups fed with the probiotic. Content of protein in the skin mucus were significantly higher in the ProC treatment than control group. Recovery rates after an air-dive test were significantly higher on the fish fed with the probiotic cells than the control group. These results show that L. casei might be used as a probiotic for fish and would help during the culture of juvenile of the Porthole livebearer P. gracilis. KEY WORDS

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In this paper is presented the percentage of fatty acids composition of three Artemia franciscana Mexican populations of epicontinentals waters; two are from natural environments (Coahuila and San Luis Potosí) and one (Texcoco) is a culture fed with Spirulina. Determination of fatty acids composition in each population, was performed by extraction of total lipid by the soxhlet method and the fatty acids methyl esters were determined by gas chromatography. The results show that Artemia of Texcoco contains the six fatty acids recommended for the culture of fish and crustaceans (16:0; 16:1; 18:1; 18:2w6; 18:3w3 and 20:5w3); Artemia from San Luis Potosí showed the poorest content in these acids and Artemia from Coahuila, although it showed a wide profile, it lacks the linolenic acid. When comparing results among the three populations with ecological data that have been published, it can be pointed out that the environment is decisive for this crustacean; Artemia from Texcoco fed with Spirulina showed the largest variety of fatty acids; the other two populations are wild, and lives in different habitats, Artemia of Coahuila is found in waters that are rich in sulfates and Artemia of San Luis Potosí lives in evaporation saltern ponds, built with stone blocks and therefore with scarce phytoplankton growth. Both Artemia populations showed deficiencies in essential fatty acids, mainly the last one.

L-ascorbyl-2-monophosphate-Na/Ca (AMP-Na/Ca) was used as a vitamin C source to investigate its ascorbic acid (L-AA) enrichment and retention in boosted Artemia biomass (AB) and squid mantle muscle (SM). Different doses of AMP-Na/Ca (500, 1000, and 1500 AMP-Na/Ca mg/kg) were gradually dissolved into the culture tanks at time 0 (T 0 ) and at each hour until Hour 6 (T 6 ). Samples of AB and SM were taken for AMP-Na/Ca and L-AA analysis at T 0 , T 1 , T 2 , T 3 , T 4, T 5 , T 6 , T 12 , and T 24 . There were no significant differences (P > 0.05) among the AB groups at T 1 . The T 6 enrichment analysis for AB resulted in significant differences (P < 0.05) in the AMP-Na/Ca content for the 1500 mg/kg treatment, in which the initial concentration (0.001 ± 0.002 mg/kg) increased by more than 16-fold. For all AB enrichment treatments, the AMP-Na/Ca content demonstrated a decrease (32-11%) for the T 6 , T 12 and T 24 analysis. The T 1 analysis for SM at the higher AMP-Na/Ca enrichment concentration registered 30 mg/kg of L-AA and decreased (27.6%) at T 6 . This study demonstrated that AB and SM can be boosted with AMP-Na/Ca.