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The relative contribution of the dietary nitrogen supplied by fish meal and a biofloc meal to the growth of Pacific white shrimp was evaluated using stable isotope analysis. Biofloculated material was obtained from an experimental tilapia culture system. Five formulated diets were supplied. Two of them consisted in isotopic controls having only fish meal or biofloc meal as protein source. Three mixed diets were formulated with varying proportions of these ingredients on a dietary nitrogen basis (75:25, 50:50 and 25:75). At the end of the trial, survival rates were similar (92-100%) but significant differences in mean final weight were observed and a negative correlation between the inclusion of biofloc meal and weight gain was evidenced. Mean final weight in shrimp fed on diet containing only fish meal was 2.8 g, while mean final weight of animals fed on diet containing 50% biofloc was 1.9 g. Isotopic mixing models indicated that all diets contributed higher proportions of dietary nitrogen from fish meal than from biofloc meal. Dietary nitrogen available in diets containing 25%, 50% and 75% of biofloc meal was incorporated in muscle tissue as 5%, 41% and 64% respectively. Diet supplying 25% of nitrogen from biofloc was the only mixed diet eliciting growth comparable to diet containing only fish meal. Lower growth and nitrogen deposition in shrimp fed on diets containing high proportions of biofloc meal were possibly associated to the use of only two protein sources and a restriction of essential amino acids.

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This study was focused on the morphological description of chame larvae from one to six days post-hatching (dph), in order to generate information that helps understanding their feeding ability in early stages. The larvae were obtained by hormonal induction of a broodstock, using implants of GnRH synthetic analogues, during the spawning season from September to November 2010. The samples were included in historesin, and stained with hematoxylin-eosin. It was described that, once the larva hatched has a large amount of yolk it is gradually absorbed (from 1 to 3 dph). At day four, there is an open oral cavity with dental structures, the eye development is complete and there was pigmentation on it, the gills are observable and the foregut was differentiated in anterior and posterior intestine, showing the presence of digestive vacuoles in the anterior intestine. By five dph the larvae has developed muscle fibers and a structure identified as the stomach. At sixth dph, it is possible to identify the pancreas, the intestinal folds, and the brush border membrane, and there were food particles and bacteria rests in the gut. Based on the above, it is concluded that the larvae of D. latifrons from the fourth dph fully developed organs and systems that help the search of food, so they are capable of starting with exogenous feeding.

This study describes the expression of genes that encode digestive enzymes (trypsin, pepsinogen, maltase-glucoamylase, sucrase-isomaltase, alkaline phosphatase and leucine aminopeptidase) using qRT-PCR in 0-to 7-day post-hatching (dph) chame (Dormitator latifrons). Additionally, adults liver and intestine were analysed for enzyme expression.Results showed that transcripts for all enzymes are present in both adult and larvae tissues. In adults, the expression of maltase-glucoamylase and sucrose-isomaltase showed the highest values in the middle intestine, while the liver and anterior and posterior intestine showed low expression levels. Other enzymes showed low expression in all tissues, with the exception of leucine aminopeptidase, which showed high expression in liver. In larvae whole-body samples of D. latifrons, maltase-glucoamylase and sucrose-isomaltase showed the highest expression from 3 to 5 dph, while other enzymes maintained low levels from hatching to 7 dph. The highest expression of disaccharidases such as maltaseglucoamylase and sucrose-isomaltase corresponded to the beginning of exogenous feeding, suggesting that this species exhibits an herbivorous profile. However, the presence of proteolytic enzymes may indicate that D. latifrons is programmed to be able to digest other substrates. This information will contribute to the development of larval feeding protocols to produce chame juveniles in laboratory conditions, as prior larval feeding essays have not been successful, using either live feeds or commercial fish larval diets. K E Y W O R D S chame, digestive enzyme, Dormitator latifrons, gene expression How to cite this article: Morelos-Castro, Román-Reyes JC, Luis-Villaseñor IE, Ramírez-Pérez JS, Rodríguez-Montes de Oca GA. Expression analyses of digestive enzymes during early development and in adults of the chame fish Dormitator latifrons. Aquac Res. 2020;51:265-275. https ://doi.

Abstract.-During early development stages, embryos and larvae of marine fish use amino acids (AA) as an energy source for aerobic catabolism and for maintaining osmolality of body fluids. Amino acid profile of eggs and larvae can be used to determine essential amino acid requirements (EAA). Better understanding the evolution of biochemical composition can improve nutritional needs at the start of exogenous feeding during early stages of fish larvae; high mortalities from nutritional deficiencies have been reported at this stage. The aim of this study was to determine the proximate chemical composition and AA profile of eggs, newly hatched larvae and larvae at 4 days post-hatch (DDE). Samples of previously mentioned stages were taken and the proximate composition and AA profile were determined using standard methods. The percentage of protein was significantly higher in the larvae 4 DDE lower in lipids. The amount of histidine, arginine and methionine was higher in the eggs and the rest of EAA was higher in the larvae at 4 DDE. The percentage of taurine was significantly higher in the eggs. These findings may serve as a guideline of EAA requirements for spotted rose snapper larvae at the onset of exogenous feeding and contribute to better feeding protocols and develop balanced diets to improve larval growth and survival.Key words: Protein, lipids, amino acids, larvae, Lutjanus guttatusResumen.-Los embriones y las larvas de los peces marinos utilizan los aminoácidos (AA) como fuente de energía para el metabolismo aeróbico y para mantener la osmolalidad de los fluidos corporales durante los primeros estadios de desarrollo. El perfil de AA de los huevos y larvas puede utilizarse como un indicador aproximado del requerimiento de aminoácidos esenciales (AAE). Conocer la evolución de la composición bioquímica de los primeros estadios de las larvas de peces proporciona una fuente valiosa para comprender mejor las necesidades nutricionales para el comienzo de la alimentación exógena; etapa donde se han reportado altas mortalidades por deficiencias nutricionales. El objetivo fue determinar la composición química proximal y perfil de AA de huevos, larvas recién eclosionadas y larvas sin vitelo. Se tomaron muestras de los estadios mencionados y se determinó su contenido bromatológico y perfil de AA utilizando métodos estándar. El porcentaje de proteína fue significativamente mayor en las larvas sin vitelo y el porcentaje de lípidos fue menor. El porcentaje de histidina, arginina y metionina fue mayor en los huevos y el resto de AAE fue mayor en las larvas sin vitelo. El porcentaje de taurina fue significativamente mayor en los huevos. Los datos obtenidos podrán utilizarse como un indicador aproximado del requerimiento de AAE de las larvas de pargo flamenco al inicio de la alimentación exógena y coadyuvar a mejorar los protocolos de alimentación y al desarrollo de dietas balanceadas para mejorar el crecimiento y supervivencia de las larvas.

RESUMEN. La producción de microalgas vivas para cultivar rotíferos constituye uno de los mayores costos de operación en la larvicultura de peces, por lo que se están desarrollando sustitutos comerciales de microalgas para la alimentación y producción de rotíferos. Se desconoce el efecto que tienen las formulaciones comerciales sobre la dinámica poblacional de rotíferos nativos del noroeste de México y en este estudio se evaluó el efecto de cuatro dietas comerciales (Espirulina, RotiMac®, Nanno 3600®, RotiGrow-Plus®) y la microalga viva Nannochloropsis sp., sobre el crecimiento poblacional y fecundidad del rotífero Brachionus ibericus (GenBank KJ949043), aislado de una granja de camarón blanco (Litopenaeus vannamei). Se realizaron cinco réplicas por tratamiento alimenticio utilizando recipientes con volumen de 12 L de agua, con temperatura de 29 ± 1°C y salinidad de 35 ± 1, respectivamente. Los resultados mostraron que durante los periodos experimentales, las dietas probadas resultaron adecuadas para alimentar a B. ibericus, con tasas de crecimiento, tiempos de duplicación, densidades máximas y fecundidades que fluctuaron entre 0.20 a 0.27 rotíferos día , respectivamente. Las diferencias entre tratamientos fueron significativas (P < 0.05); los menores tiempos de duplicación y las mayores tasas de crecimiento, fecundidad y densidad poblacional fueron obtenidas con RotiGrow-Plus ® , pero el tiempo de duplicación y la tasa de crecimiento con RotiGrow-Plus ® no fueron significativamente diferentes (P > 0.05) a las obtenidas con Nanno 3600 ® .Palabras clave: Brachionus ibericus, Nannochloropsis, rotíferos, dinámica poblacional, dietas comerciales. Population dynamics of rotifer Brachionus ibericus isolated from shrimp ponds, fed with different dietsABSTRACT. The production of live microalgae to cultivate rotifers is one of the largest operating costs in fish hatcheries. Commercial substitutes of microalgae are being developed to feed and produce rotifers. The effect of commercial formulations on the population dynamics of native rotifers of northwestern Mexico is unknown, so in this study the effect of four commercial diets (Spirulina, RotiMac®, Nanno 3600®, RotiGrow-Plus®) was evaluated as well as the live macroalgae Nannochloropsis sp., on the population growth and fecundity of the rotifer Brachionus ibericus (GenBank KJ949043), isolated from a white shrimp farm (Litopenaeus vannamei). Five replicates per dietary treatment were performed using 12 L containers with temperature of 29 ± 1°C and salinity of 35 ± 1 respectively. The results showed that during the experimental period, the diets tested were suitable to feed B. ibericus, with mean growth rates, duplication times, maximum densities and fecundities that ranged from 0.20 to 0.27 rotifers day-1, 2.60 to 3.42 days, 0.16 to 0.39 eggs per female and 215.4 to 357.0 rotifers mL -1 , respectively. Differences between treatments were significant (P < 0.05); lower doubling times and higher growth rates, fecundities and population densities were obtained with RotiGrow-P...

The stomachs of 464 speckled guitarfish Rhinobatos glaucostigma were sampled from the south-eastern Gulf of California (GC) to determine diet composition. Numerical indices and prey-specific index of relative importance ((%I)PSIR ) were used to determine the feeding strategy of the species. An analysis of similarity (ANOSIM) was used to determine differences in diet with respect to sex, season (dry or rainy) and maturity stages (immature or mature). The diversity and niche breadth (by sex, season and maturity) and a general trophic level were determined. The overall diet was dominated by shrimps ((%I)PSIR  = 43.47), amphipods ((%I)PSIR  = 18.89) and crabs ((%I)PSIR  = 18.07). ANOSIM demonstrated differences in the diet by maturity and season, but not by sex. Rainy and dry season diets were dominated by shrimps and amphipods, respectively. Immature specimens fed mainly on amphipods, whereas mature fish preferred shrimps and crabs. Rhinobatos glaucostigma showed a narrow niche breadth with an intermediary trophic level (TL  = 3.72) and can be considered as a secondary consumer in the soft-bottom demersal community of the south-east GC. Understanding the feeding habits and trophic level of R. glaucostigma is vital to help identify the segments of the population vulnerable to overfishing by artisanal and industrial fisheries, and to aid in conservation and management of this elasmobranch.