Intestinal glucose transport in carnivorous and herbivorous marine fishes
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The influx and transepithelial movements of glucose and their effects on the electrophysiology and Na transport in upper and lower intestines of the herbivorous surgeonfish, Acanthurus mata , and carnivorous eel, Gymnothorax undulatus , were measured. The K t G and J max G of glucose influx into the tissues were higher in the surgeonfish upper intestine than in the surgeonfish lower intestine or in both segments of the eel intestine. A prominent diffusion-like transport component was also measured in all four segments during influx experiments. Net transepithelial glucose fluxes (0.05 mM) were greater in eel intestine than in those of the surgeonfish largely due to an apparent lower apical membrane permeability of the former coincident with reduced backflux of glucose from epithelium to lumen. All four stripped intestinal segments exhibited non-significant (from zero; P >0.05) or small, serosa-negative transepithelial potential differences (-0.1 to -2.2 mV), and low transepithelial resistances (40–88 O cm -2 ). Each tissue displayed significant ( P P >0.05) change the transepithelial resistance, but did induce a significant ( P J net Na with added luminal glucose, these increased net cation fluxes were not quite significant ( P >0.05). It is concluded that coupled Na-glucose transport occurs in these tissues, but that metabolic enhancement of unrelated current-generating mechanisms also takes place and may modify depolarizing effects of organic solute transfer.
CitationFerraris, R. P., & Ahearn, G. A. (1983). Intestinal glucose transport in carnivorous and herbivorous marine fishes.
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ArticleRP Ferraris & GA Ahearn -
Comparative Biochemistry and Physiology - Part A: Physiology, 1984 - Elsevier1. Morphological properties of fish intestines vary with diet. Carnivores have short guts with highly elaborate mucosal folding in the upper intestines; herbivores have long guts which appear structurally uniform from stomach to rectum. 2. Brush border membranes of many fish intestines display at least two transport processes for each organic solute, one an Na+-dependent, saturable carrier mechanism, and the other a non-saturable influx pathway which may be simple diffusion. 3. Intestinal epithelial cells from freshwater fish can accumulate nutrients to concentrations in excess of those in the gut lumen; those of marine fish can not. 4. Net transepithelial nutrient transport in upper intestine is greater in freshwater fish than in marine forms as a result of considerable solute backflux from epithelium to lumen in the latter. 5. In many fish the lower intestine displays a significant net transmural flux of nutrients that may contribute to total organic solute absorption. 6. Intestines of freshwater fish have a serosa positive (relative to mucosa) electrical potential difference; marine fish display a negative serosa. 7. Addition of organic solutes to intestines of freshwater fish hyperpolarizes the electrically positive serosa; in marine forms a depolarization of the serosa negative potential occurs. In both cases this appears due to increased net transmural sodium transport coupled to net nutrient flow.
ArticleOptimum packing conditions for the transport of hatchery-reared and wild grouper larvae were investigated under simulated condition or actual air transport. Simulation of transport motion was done through the use of an electric orbit shaker to identify the best packing conditions for the transport of grouper larvae at various ages. Simulated transport was conducted in hatchery-reared grouper larvae at day 35 (mean TL=14.73 mm), 45 (mean TL=15.23 mm) and 60 (mean TL=28.16 mm) at packing densities of 50, 100 and 200 larvae l−1 and at high (28 °C) or low (23 °C) temperatures. Packing density of 50 larvae l−1 was best for 45- and 60-day-old larvae 8 h transport at low temperature. However, packing density could be increased to a maximum of 100 larvae l−1 8 h transport at 23 °C with mortality rates ranging from 2.3% to 5.3%. The increase in total NH3 level was dependent on temperature, packing density and size of larvae. High packing density (100–200 larvae l−1) and temperature (28 °C) resulted in increased NH3 level and mortality rates during transport. In addition, regardless of the temperature, NH3 levels were consistently higher for 60-day-old larvae. Day-60 grouper larvae displayed strong resistance to handling/mechanical stress compared to 35-day-old larvae probably because most are already fully metamorphosed at this stage. Based on these results, a packing density of 50 larvae l−1, a temperature of 23 °C and larval age of 60 days were considered as the best transport conditions for hatchery-reared grouper larvae. When these transport conditions were used in experiment 2, for 26-day-old hormone-metamorphosed, 60-day-old naturally metamorphosed or 60-day-old pre-metamorphosing hatchery-reared grouper larvae, a 100% survival rate was attained in all treatments. Seven days of hormone (T3) treatment did not accelerate metamorphosis of wild-caught transparent grouper larvae (tinies) significantly. Survival rates of hormone-treated transparent tinies (H-tinies), untreated black tinies (B-tinies) and untreated transparent tinies (T-tinies) were also similar after 8–9 h air transport (experiment 3). The results of the current study suggest that T3 treatment did not affect the performance of hatchery-reared and wild-caught transparent tinies/larvae during transport. In addition, mass mortalities of these transported tinies during the nursery phase were associated with nutritional aspect and the sudden confinement of these undomesticated wild-caught grouper to small space rather than transport or hormone treatment effects.
Critical factors influencing survival and hatching of milkfish (Chanos chanos Forsskal) eggs during simulated transport The effects of loading density, length of transit time, temperature and salinity on milkfish (Chanos chanos Forsskal) eggs during simulated transport were examined. Rocking motion approximating conditions of transport of eggs collected from milkfish broodstock floating net cages to a hatchery was simulated using a laboratory orbit shaker. Loading densities of more than 7000 eggs/l in shipping bags resulted in decreased rates of survival and correspondingly lower hatching rates. Prolonged shaking simulating extended periods of egg transport also resulted in low egg survival and hatching rates compared to fertilized eggs not subjected to simulated transport. Egg survival after simulated transport at 20°C was lower than at 28°C, except at 20 ppt salinity, where survival was equal. Egg survival at 20°C progressively increased with declining salinity levels whereas high egg survival rates were observed after 2 h of simulated egg transport at 28°C and at the three salinities tested. Hatching rates of fertilized eggs after simulated transport were higher at 28°C than at 20°C regardless of salinity. Neither salinity nor its interaction with temperature affected hatching rates of eggs after simulated transport. These results indicate that survival and hatching of fertilized milkfish eggs after simulated transport is influenced by loading density, transport time, temperature and, to some degree, the salinity of the water. Based on these results, guidelines for handling and transporting milkfish eggs are given.