Interactions between effects of environmental chemicals and natural stressors: A review

Denitrification in recirculating systems: Theory and applications

Nitrogen biogeochemistry of aquaculture ponds

Nitrite is a potential problem in aquatic environments. Freshwater fish actively take up nitrite across the gills, leading to high internal concentrations. Seawater fish are less susceptible but do take up nitrite across intestine and gills. Nitrite has multiple physiological effects. Its uptake is at the expense of chloride, leading to chloride depletion. Nitrite also activates efflux of potassium from skeletal muscle and erythrocytes, disturbing intracellular and extracellular K(+) levels. Nitrite transfer across the erythrocytic membrane leads to oxidation of haemoglobin to methaemoglobin (metHb), compromising blood O(2) transport. Other haem proteins are also oxidised. Hyperventilation is observed, and eventually tissue O(2) shortage becomes reflected in elevated lactate concentrations. Heart rate increases rapidly, before any significant elevations in metHb or extracellular potassium occur. This suggests nitrite-induced vasodilation (possibly via nitric oxide generated from nitrite) that is countered by increased cardiac pumping to re-establish blood pressure. Nitrite can form and/or mimic nitric oxide and thereby interfere with processes regulated by this local hormone. Steroid hormone synthesis may be inhibited, while changes in ammonia and urea levels and excretion rates reflect an influence of nitrite on nitrogen metabolism. Detoxification of nitrite occurs via endogenous oxidation to nitrate, and elimination of nitrite takes place both via gills and urine. The susceptibility to nitrite varies between species and in some cases also within species. Rainbow trout fall into two groups with regard to susceptibility and physiological response. These two groups are not related to sex but show significant different nitrite uptake rates.

Nitrite disrupts multiple physiological functions in aquatic animals.

This review gives an updated picture of each class of phenolic compounds and their properties. The most common classification implies the subdivision of phenolics in two main groups: flavonoids (e.g., anthocyanins, flavanols, flavanones, flavonols, flavonones, and isoflavones) and non-flavonoids (e.g., phenolic acids, xanthones, stilbens, lignans, and tannins) polyphenols. The great interest in polyphenols is associated with their high potential application for food preservation and for therapeutic beneficial use. The relationship between polyphenol intake and human health has been exploited with special reference to cardiovascular diseases, hypertension, diabetes, metabolic syndrome, obesity, and cancer. The use of current existing databases of bioactive compounds including polyphenols is described as key tools for human health research.

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Polyphenols: A concise overview on the chemistry, occurrence, and human health

Tolerance of coho salmon (Oncorhynchus kisutch) to nitrite was increased when the concentration of chloride ion in the environment was high. The results of flow-through bioassays revealed that no mortality occurred when yearling coho salmon were subjected to nitrite-nitrogen (NO2−–N) of 29.8 mg/l and chloride (Cl−) of 261.3 mg/l for 48 h. When yearling coho salmon were exposed to 3.8 mg/l NO2−–N and 2.5 mg/l Cl− for 12 h, the resultant mortality was 58.3%. Possibly, chloride competes with nitrite for transport across the gills and integumental tissues, thereby interfering with the onset of nitrite-induced methemoglobinemia.

Protective Effect of Chloride on Nitrite Toxicity to Coho Salmon (Oncorhynchus kisutch)

The influence of ammonia on the oxygen delivery system of coho salmon hemoglobin

The effect of the Maillard browning reaction in the diet of rainbow trout (Salmo gairdnerA­)on growth and amino acid availability was investigated. Chemical and enzymatic hydrolysis methods were applied for the detection of the losses of amino acids in a model protein browning system. Arginine and lysine ex hibited the greatest losses in the mixture of fish protein isolate and glucose stored for 40 d at 37 Â°C. The apparent digestibility and absorption of individual amino acids, particularly lysine, was lower in trout fed browned protein than in those fed the con trol protein. Plasma lysine levels were significantly depressed, while the plasma levels of glucose and most other amino acids were elevated in relation to the loss in nutritive value of dietary protein after browning. The early Maillard reaction derivative of lysine, Â«-deoxy-fructosyl-lysine, was recovered from browned protein (by using the in vitro enzymatic hydrolysis procedure) and from the plasma of trout fed browned pro tein. Analysis of plasma free amino acids provided an indication of lysine bioavail- ability and identified lysine as the first-limiting amino acid in the diets containing browned protein. J. Nutr. 115: 1589-1599, 1985.

Effect of maillard browning reaction on protein utilization and plasma amino acid response by rainbow trout (Salmo gairdneri)

Effect of Chloride Ion Concentration and pH on the Transport of Nitrite across the Gill Epithelia of Coho Salmon

In recent years the fish by‐products industry has grown more rapidly than any other segment of the world's fisheries. Production of fish meal, the primary product of the industry and an important feed ingredient, rose from 1,525,000 metric tons in 1958 to 5,080,000 metric tons in 1968. This tremendous increase in production was the result of improved fishing methods, expansion of established fisheries, and the development of new fisheries, particularly the anchoveta fishery of Chile and Peru. Although markets for fish meal were severely disrupted during the early part of the expansion, they subsequently exhibited a high order inelasticity and provide the basis for profitable operations.

Thomas L. Meade

Papers

Protective Effect of Chloride on Nitrite Toxicity to Coho Salmon (Oncorhynchus kisutch)

The influence of ammonia on the oxygen delivery system of coho salmon hemoglobin

Effect of maillard browning reaction on protein utilization and plasma amino acid response by rainbow trout (Salmo gairdneri)

Effect of Chloride Ion Concentration and pH on the Transport of Nitrite across the Gill Epithelia of Coho Salmon

Recent advances in the fish by‐products industry