Mineral toxicity of fish can occur due to presence of different toxic components in their diet. Diseases occur due to these toxic components are known as dietary diseases.

2. 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.

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

4. • 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

5. • 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

6. 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

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

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

9. • 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.

10. • 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

11. Figure: Scoliosis in perch fish
Figure: Lordotic gilthead seabream fry

12. • 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

13. 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

14. • 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

15. Figure: Vacuolated hepatocytes

16. • 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

17. • 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