TOXIC COMPONENTS OF THE DIET OF TELEOSTS

Dietary Mineral Toxicity

MD. ATICK CHOWDHURY

Dietary Mineral Toxicity

Excessive levels of minerals in the diet can be responsible for a number of well recognized and not infrequent disease conditions. Unless the toxicant level is overwhelming, the clinical signs are those so often associated with nutritional disease, namely reduced growth and poor conversion, often with darkening of skin colour.

Dietary Toxic Minerals

• Copper• Calcium• Selenium• Lead• Cadmium• Iron• Zinc• Chromium

Sources of Toxic Minerals

• Mining and processing• Smelting plants• Rolling mills plants for the surface treatment of

metals• Film, textile and leather industries and other

sources• Burning of fossil fuels• By the exhaust gases of motor vehicles and from

other sources

Copper (Cu) Toxicity

• LC50s are around 0.001 to 0.01 mg/litre• Toxicity signs associated with reduced growth

(dietary level above 15 mg/kg)

Figure: Control gill lamella of Esomus danricus

Copper (Cu) Toxicity

Figure: Alterations in secondary gill lamellae exposed to 5.5mg/l of copper

Figure: Alterations in gill of Esomus exposed to sub-lethal concentration (0.55mg/L) of copper

Calcium (Ca) Toxicity

• Disease caused due to calcium toxicity are-• Hypercalcinosis• Nephrocalcinosis• Lithiasis• Cholelithiasis

Calcium (Ca) Toxicity

Figure: Renal calcification (nefrocalcinos) in the rear part of the kidney in rainbow trout (Oncorhynchus mykiss).

Selenium (Se) Toxicity

• Nephrocalcinosis: Dietary selenium toxicity (13 mg/g) in rainbow trout resulted in an increased level of calcium and magnesium in kidney and elevated levels of magnesium in liver and thus nephrocalcinosis occur in the rear part of fish kidney.

Lead (Pb) Toxicity• Acute toxic concentrations range from-

• 1 to 10 mg/litre for salmonids• 10 to 100 mg/litre for cyprinids

• Acute lead toxicity is characterized initially by damage to the gill epithelium

• Diseases due to Pb toxicity-• Scoliosis• Lordosis • Black tail• Anaemia• Degeneration of caudal fin

• The affected fish are killed by suffocation

Lead (Pb) Toxicity

Figure: Scoliosis in perch fishFigure: Lordotic gilthead seabream fry

Cadmium (Cd) Toxicity

• Disease occurred due to cadmium toxicity:• Hypocalcaemia• Hyperexcitability• Osteoporosis

• An adverse influence of long exposure to cadmium upon the maturation, hatchability and development of larvae in rainbow trout was recorded at concentrations as low as 0.002 mg/litre

Cadmium (Cd) Toxicity

Figure: Representative Antarctic notothenioid fish. The Antarctic rockcod, Notothenia coriiceps (top), is red-blooded and possesses a robustly mineralized skeleton. The white-blooded icefish, Chaenocephalus aceratus (bottom), is profoundly anemic and osteopenic

Iron (Fe) Toxicity

• Vacuolated hepatocytes occur due to iron toxicity• Soluble ferrous iron can be oxidized to insoluble

ferric compounds which then cover the gill lamellae and inhibit respiration

• At a low water temperature and in the presence of iron, iron-depositing bacteria will multiply rapidly on the gills and further contribute to the oxidation of ferrous iron compounds

Iron (Fe) Toxicity

Figure: Vacuolated hepatocytes

Zinc (Zn) Toxicity

• The lethal concentrations are around 0.1 mg/litre for salmonids (some authors even suggest a level of 0.01 mg/litre) and 0.5 to 1.0 mg/litre for cyprinids

• Reduced growth (dietary level above 300mg/kg)• Rainbow trout and brown trout and especially their

fry are extremely sensitive to zinc and its compounds• Zinc poisoning of fish is most frequently encountered

in trout culture

Chromium (Cr) Toxicity

• LC50s 2.0 to 7.5 mg/litre• Reduced growth and feed efficiency• Acute poisoning exhibits-• Body surface covering with mucus• Respiratory epithelium of the gills is damaged• Fish die with symptoms of suffocation• Fish suffering from chronic chromium intoxication

accumulate an orange-yellow liquid in their body cavity