The characterisation of digestive proteases in native freshwater fish such as the Mayan cichlid Cichlasoma urophthalmus provides scientific elements that may be used to design balanced feed that matches with the digestive capacity of the fish. The purpose of this study was to characterise the digestive proteases, including the effect of the pH and the temperature on enzyme activity and stability, as well as the effect of inhibitors using multienzymatic extracts of the stomach and intestine of C. urophthalmus juveniles. Results showed that the optimum activities of the acid and alkaline proteases occurred at pH values of 3 and 9, respectively, whereas their optimum temperatures were 55 and 65 °C, respectively. The acid proteases were most stable at pH values of 2–3 and at temperatures of 35–45 °C, whereas the alkaline proteases were most stable at pH values of 6–9 and at 25–55 °C. The inhibition assays recorded a residual activity of 4% with pepstatin A for the acid proteases. The inhibition of the alkaline proteases was greater than 80% with TPCK, TLCK, EDTA and ovalbumin, and of 60 and 43.8% with PMSF and SBT1, respectively. The results obtained in this study make it possible to state that C. urophthalmus has a sufficiently complete digestive enzyme machinery to degrade food items characteristic of an omnivorous fish species, although specimens showed a tendency to carnivory.
Summary The ontogeny of the digestive tract in Cichlasoma urophthalmus was studied by means of optical microscopy from hatching to 30 days post‐hatching (dph; 855 degree days, dd). The development of the digestive system in this precocial species was a very intense and asynchronous process, which proceeded from both distal ends interiorly. At hatching, the digestive tract consisted of a straight tube with a smooth lumen dorsally attached to the yolk‐sac. The digestive accessory glands were already differentiated and eosinophilic zymogen granules were visible in the exocrine pancreas. At the onset of exogenous feeding between 5 and 6 dph (142.5–171.0 cumulative thermal units, CTU), the buccopharynx, oesophagus, intestine, liver and pancreas were almost completely differentiated, with the exception of the gastric stomach that completed its differentiation between 11 and 14 dph (313.5–399.0 CTU). The development of gastric glands at 14 dph and the differentiation of the stomach in the fundic, cardiac and pyloric regions at 19 dph (541.5 CTU) were the last major events in digestive tract development and designated the onset of the juvenile period. Remnants of yolk were still detected until 16 dph (456.0 CTU), indicating a long period of mixed nutrition that lasted between 10 and 11 days (285.0–313.5 CTU). The results of the organogenesis of larvae complement previous data on the functionality of the digestive system and represent a useful tool for establishing the functional systemic capabilities and physiological requirements of larvae to ensure optimal welfare and growth under aquaculture conditions, which might be useful for improving current larval rearing practices for this cichlid species.
SUMMARY:The description of the embryonic and larval development was based on 30 eggs and 30 larvae. Breeders were collected on the Usumacinta River, Tabasco, Mexico and were subjected to manual fertilization in May 2011. Fertilized eggs were spherical, pelagic, translucent and non-adhesive and had an average diameter of 1.07 mm (SD = 0.10), showing a concentric lipid droplet of 0.85 mm (SD = 0.02). The embryo occupied 100% of the perivitelline space at hour 14:08 post-fertilization and the egg measured 1.18 mm (SD = 0.14) at this stage. Eclosion started 17 hours post-fertilization when larvae had a length of 2.54 mm (SD = 0.66). Eight preanal and 13 postanal myomeres were observed exhibiting a light brown color. The morphologic characters recorded in this study are similar to the anatomy of embryos and larvae of the Sciaenidae family. The diameter of the eggs and the length of the larvae for A. grunniens are slightly larger than other Sciaenidae species: A. regius, C. striatus, B. chrysora, C. regalis, L. xanthurus, P. cromis, G. lineatus and S. ocellatus. This is the first study of its kind and its results contribute to the knowledge of the species reproductive biology.
Sciaenids, commonly known as drums, are a group of coastal marine and freshwater fishes consisting of 275 species belonging to 70 genera that support commercial and sports fisheries around the world. Although most drums inhabit marine waters, the freshwater drum Aplodinotus grunniens Rafinesque; 1819 is the only sciaenid to exclusively inhabit freshwater environments. This species has the largest latitudinal range for freshwater fish in North America, with a distribution ranging from the Nelson River in Canada to the Usumacinta River, located between Mexico and Guatemala (Chad et al., 2007;Miller et al., 2005). Because of the economic importance of A. grunniens as a fishery resource,
ABSTRACT. Aplodinotus grunniens supports a sustained artisanal shery in the Usumacinta River; however, there are few studies to understand the population dynamics of the species. Relevant aspects of the reproductive biology were documented over an annual cycle, using 593 specimens captured with seine nets. The results indicate that females had a median TL of 32.05 cm, while males had 29.71 cm. The estimated sex ratio was 1.2:1 (males: females). The length-weight relationship showed signicant dierence between sexes, observing an allometric-type growth represented by TW=0.0013(TL)with 89.17 % of the data variability explained by the model. Gonadosomatic index (GSI) in females was higher in September (4.29), with males displaying a higher GSI in October (1.02). The highest HSI increase in females was observed in October (1.0). The estimated relative fecundity was 138.74 (± 74.30) oocytes/g of female weight. The macroscopic analysis of gonads indicates that the highest frequency of mature females occurs in June (75 %), while in males it takes place in March and June (35 %). The estimated L 50 for females was 31.89 cm (TL) and 28.78 cm (TL) for males. Though A. grunniens reproduces throughout the year, reproductive peaks coincide with the period when the river level decreases, and shing increases considerably. Hence, preventive measures must be applied in regards to the size of the species at capture and the exploitation volumes of this resource.Key words: Fishery biology, reproduction, Usumacinta river RESUMEN. Aplodinotus grunniens soporta una pesquería artesanal sostenida en el río Usumacinta; sin embargo, existen pocos estudios que permitan entender su dinámica poblacional. Se documentaron aspectos relevantes de la biología reproductiva a lo largo de un ciclo anual, empleandose 593 especímenes capturados con redes de cerco. Los resultados indican que las hembras presentaron una mediana de 32.05 cm de LT y los machos de 29.71 cm. La proporción sexual estimada fue de 1.2:1 (machos: hembras). La relación longitud-peso presentó diferencias signicativas entre sexos, observándose un crecimiento de tipo alométrico representado por TW=0.0013(TL) 3.5985 , con un 89.17 % de la variabilidad de los datos explicada por el modelo. El índice gonadosomático (IGS) en hembras fue mayor en septiembre (4.29) y en machos en octubre (1.02), mientras que el mayor incremento de IHP en hembras se observó en octubre (1.0). La fecundidad relativa estimada fue de 138.74 (±74.30) ovocitos/g de peso de la hembra. El análisis macroscópico de gónadas indica que la mayor frecuencia de organismos maduros en hembras se presenta en junio (75 %) y en machos en los meses de marzo y junio (35 %). La L 50 estimada para hembras fue de 31.89 cm (LT) y para los machos de 28.78 cm (LT). A. grunniens se reproduce la mayor parte del año, con picos reproductivos que coinciden con la disminución en los niveles del río y un considerable aumento de la pesca. Por lo tanto, se deben establecer medidas preventivas sobre su talla de captura y los volúmenes de exp...
Aplodinotus grunniens represent a crucial artisanal fishery in the Usumacinta River’s middle basin that generates food and a subsistence economy. This study aimed to create a model that best describes growth for A. grunniens and provides information on the growth of this poorly known pecies from the Usumacinta River. Data collection was carried out over one year through monthly sampling. A total of 447 specimens were collected from January to December 2017. Von Bertalanffy’s growth constants were calculated by separate sexes using linear fit and the non-linear Levenberg-Marquardt method. Hotelling’s T-squared test showed that growth was significantly faster in females than males. The estimated age at first maturity was two years in males and three in females. Considering the age reported for A. grunniens in other studies, the age determined in this study indicates that the population could be overexploited. Larger fish are more vulnerable to fishing pressure, mainly during their highest reproductive activity when they aggregate for spawning. More research is needed to evaluate the population status, catch per unit effort, distribution, and abundance of adults, juveniles, and larvae.
Peces de importancia comercial en Tabasco, México, están siendo infestados de manera natural con parásitos de pentastómidos. En la presente investigación se dan a conocer la morfología, los índices ecológicos de infección de la larva en tres especies de valor comercial. Los peces bajo estudio son mojarras de interés alimenticio como Parachromis managuensis, Petenia splendida y Gobiomorus dormitor. Se registró un total de 30 larvas de pentastómidos. La mayor prevalencia registrada en estos fue en G. dormitor de 30% y 35%, durante los años 2005 y 2015, respectivamente. La prevalencia por larvas de pentastómido ha incrementado en las especies estudiadas. Por tanto, se recomienda evitar el consumo de ejemplares crudos en diferentes platillos, y se propone al sector salud tomar las medidas precautorias ante la sociedad para evitar infección a humanos por esta larva.
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