ABSTRACT In the commercial culture of Nile tilapia (Oreochromis niloticus), monosex, all-male populations obtained through steroid sex reversal is the most commercially used method to eliminate unwanted reproduction and increase final productive and economic yield. However, the rapid growth of Nile tilapia culture has led, in some regions, to an increase in infectious diseases and mortality in all stages of commercial culture. To reduce this, without the abuse of antibiotics or similar substances, feed additives are currently used in all stages, including the fry period, during the sex reversal process. The objective of this work was to evaluate the effect of synthetic steroid Fluoxymesterone (FM) at various concentrations in combination with a commercial Blend of additives (BA) on the percentage of males, growth, and survival of Nile tilapia fry. Five treatments (FM20, FM5+BA, FM10+BA, FM20+BA, and BA+FM20) and a control group were evaluated. Treatments differ in the order in which the commercial blend (2 g) was added and the FM concentration (5, 10, and 20 mg). The feeding trial lasted for 30 days using a sexually undifferentiated population of Nile tilapia. The results showed a decrease in the percentage of males in all treatments supplemented with the BA, compared to the FM20 treatment (containing 20 mg without BA). Growth and survival were positively affected by the inclusion of the BA in all treatments, showing higher values than those observed in the control group. Further studies are necessary to determine the FM-BA interaction.

RESUMO: Buscamos por um impacto positivo de utilidade nas espécies invasoras como Pterygoplichthys spp. Foi avaliado o nível ótimo de substituição da farinha de sardinha (SM) pela farinha de Pterygoplichthys spp. (PML) em dietas práticas para tilápia do Nilo (Oreochromis niloticus). Foram utilizadas seis dietas experimentais; 50% PLM-50% SM, 60% PLM-40% SM, 70% PLM-30% SM, 80% PLM-20% SM, 90% PLM-10% SM e 100% PLM-0% SM. Em sistema de recirculação foram colocados 270 filhotes de tilápia machos (0.7 ± 0.1 g). As dietas foram triplicadas, o experimento durou 56 dias com amostragem a cada 14 dias, não houve diferença estatística para o crescimento. No final do experimento, foram determinados SGR, ADG, CF, WG, DFI, FCR e PER, não encontrando diferenças significativas (P> 0,05), embora tenha havido uma tendência indicando maior WG e PER na dieta 90% PLM-10% SM (93,56 ± 0,43% e 8,44 ± 1,18 g). A sobrevida foi superior a 90%, sem diferenças significativas. Além disso, não houve diferenças significativas na composição proximal de todo o peixe, enquanto o aparente coeficiente de digestibilidade de proteínas (81-90%) e lipídios (87-93%) também não mostrou diferenças significativas. Podemos concluir que o uso de 100% de farinha de Pterygoplichthys spp. pode substituir 100% de farinha de sardinha na alimentação de jovens O. niloticus sem afetar a sobrevivência, o crescimento, a composição química e a digestibilidade aparente dos nutrientes.

ABSTRACT: We search for positive utility impact on the invasive species Pterygoplichthys spp. The optimal level of replacement of sardine meal (SM) by Pterygoplichthys spp. meal (PLM) in practical feeds for fry of Nile tilapia (Oreochromis niloticus) was evaluated. We evaluated six experimental diets: 50% PLM-50% SM, 60% PLM-40% SM, 70% PLM-30% SM, 80% PLM-20% SM, 90% PLM-10% SM and 100% PLM-0% SM. In a recirculation system, 270 sex-reversed tilapia fry were used (0.7 ± 0.1 g). Diets were administered in triplicate and the experiment lasted 56 days with sampling every 14 days. There were no statistical differences in growth. At the end of the experiment, the SGR, ADG, CF, WG, DFI, FCR and PER were determined without significant differences (P > 0.05) between treatments, but there was a tendency that could indicated higher WG and PER in the 90% PLM-10% SM treatment (93.56 ± 0.43% and 8.44 ± 1.18 g, respectively). All survival rates were higher than 90% with no significant differences. Additionally, there were no statistical differences in the chemical composition of the whole fish, while apparent digestibility coefficients of protein (81-90%) and lipids (87-93%) also showed no significant differences. We concluded that 100% PLM can replace 100% SM in feeding fry of O. niloticus without affecting their survival, growth or chemical composition or the apparent digestibility of nutrients.

ABSTRACT. This research study is focused on the lipid requirements of Petenia splendida (0.65 ± 0.19 g) juveniles. Fish were fed with trout commercial diet (Silver Cup™ - 45% protein and 16% lipids), as control diet - CD (which is usually used to feed this species at commercial scale), and four isoproteic (45% crude protein) diet formulated with different lipid levels (5, 10, 15 and 20%). Diets were administered for 60 days by triplicate per treatment. Our results showed that fish fed with 10, 15 and 20% lipid levels were significantly higher (P < 0.05) in average weight and total length. Same treatments were significantly lower (P < 0.05) in terms of FCR compared to those shown in 5% and CD. However, fish fed 20% lipid level, showed a significant decrease in WG and a significant (P < 0.05) increase in FCR compared to those shown in 15% lipid level. Fish fed with 15% showed the highest weight gain and the lowest FCR compared with the rest of the treatments. Lipid efficiency ratio (LER) showed significant (P < 0.05) differences among experimental groups. Compared to other diets containing lipid levels (5, 10, and 20%) fish fed 15% diet recorded the lowest protein and lipid content in whole body. Additionally, based on second order polynomial regression analysis of WG, it was demonstrated that 16.2% lipid provides an optimal growth for P. splendida.

The systematics of the marine catfish of the family Ariidae is controversial because at the present time the number of species and genera in the family, or their relationships, remain uncertain. Phylogenetic relationships among five representative species of marine catfish of the family Ariidae from both the Pacific and the Atlantic coasts of Mexico were assessed by the analysis of the variability in 21 alloenzymatic loci, and by the comparison of the electrophoretic patterns of whole muscle proteins. Interspecific genetic divergence levels obtained by both electrophoretic methods showed a clear separation among the genera Cathorops, Bagre and Ariopsis, as well as in the studied species of Cathorops and Ariopsis, with Bagre marinus showing a greater genetic similarity with the Ariopsis group. Finally, our results contribute to the definition of the presence of this species in the coasts of the Gulf of Mexico.

La sistemática de los bagres marinos pertenecientes a la familia Ariidae es controversial, porque hasta la actualidad, no se conoce con exactitud el número de especies y géneros existentes en la familia, ni las relaciones que se establecen entre ellos. En el presente trabajo se estudiaron las relaciones filogenéticas entre cinco especies representativas de bagres marinos de la familia Ariidae, de ambas costas del Pacífico y del Atlántico Mexicano. El mencionado análisis se llevó a cabo mediante el análisis de la variabilidad en 21 loci aloenzimáticos y a través de la comparación de patrones electroforéticos de proteínas totales de músculo. Los niveles de divergencia interespecífica obtenidos por ambos métodos electroforéticos mostraron una clara separación entre los géneros Cathorops, Bagre y Ariopsis, así como entre las especies estudiadas de Cathorops y Ariopsis con Bagre marinus, mostrando una mayor similitud genética con el grupo Ariopsis. Los resultados obtenidos en este estudio contribuyen al establecimiento de la presencia de estas especies a lo largo de las costas del Golfo de México.