Gut ph and digestive strategies in estuarine grey mullet (Mugilidae) and tilapia (Cichlidae)

Abstract

Tilapia guineensis, which feeds on leafy material, and Sarotherodon melanothron, which utilizes blue-green algae, were both capable of producing a pH 2 or less in the stomach which could contribute to the lysis and digestion of blue-green algae and bacteria. Of the grey mullets investigated, Liza fakipinnis had a gastric pH 33-45, which may not be low enough to cause cell lysis, whilst Liza dumerili, Mugif cephalus and Mugil curema all had stomach, caecal and intestinal pH's of 7-8.5. Grey mullet appear to have a different digestive strategy to tilapia and may rely upon the establishment of a ' colloid mill ' in the stomach.

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in a freshwater snail (Bellamya aeruginosa) from a large shallow, eutrophic lake of the subtropical China

“…In an Egyptian fish farm, MC contents were 1120 mg g ÿ1 DW in Microcystis blooms, and 8.21 mg g ÿ1 DW (the maximum) in the gut of the phytoplanktivorous tilapia, indicating a difference of 136.4 times. It should be noted, however, that tilapia have a stomach with pH value as low as 1.25 or even 1.0 in the stomach fluids during digestion (Payne, 1978), suggesting the possibility of active degradation of MCs in the stomach and thus the presence of low MC contents in the guts.…”

Gut contents of silver carp, Hypophthalmichthys molitrix, and the disruption of a centric diatom, Cyclotella, on passage through the esophagus and intestine

“…Tilapia are a good example of species which rely on acid hydrolysis, i.e., they are particularly well adapted to disrupt cyanobacterium cell walls because pH values as low as 1.25 or even 1.0 are present in the stomach fluids Ž . during active digestion Moriarty et al, 1973;Caulton, 1976;Payne, 1978 . However, in stomachless filter-feeding fishes such as silver carp, the pH of the gut fluids is usually ) 6.…”

Produccion de tilapia nilotica (Oreochromis niloticus L.) utilizando hojas de chaya (Cnidoscolus chayamansa

“…Esta habilidad se atribuye a que, a diferencia de otros peces, las tilapias tienen una buena capacidad para digerir y asimilar carbohidratos, lo cual depende de la cantidad de fibra del alimento, frecuencia de alimentación, tamaño de los peces y tipo de carbohidrato (Shiau, 1997). Se considera que pueden utilizar adecuadamente alimentos de origen vegetal debido a su capacidad de producir en sus estómagos un pH2 o menor, ayudando a la lisis y digestión de este tipo de materiales, incluyendo a las algas verde-azul (Payne, 1978), e inclusive digerir el contenido celular sin lisar las paredes celulósicas (Bowen, 1981;Ekpo & Bender, 1989;Horn & Messer, 1992). Estos factores indican entonces que este organismo puede ser cultivado en sistemas de producción a baja escala, por lo que se pueden utilizar vegetales frescos disponibles localmente, a fin de minimizar los costos de alimentación.…”