Fish Diseases and Management

2.2.19 The Excretory system to be done 

Kidney

It has mainly three functions.

• Excretion
• Haematopoesis
• Endocrine

The basic functional unit of kidney is the nephron. Nephron is a tubular structure having a cup like Bowman’s capsule which contains glomerulus, which has coiled branched capillaries. Head kidney functions for haematopoiesis while mid kidney and posterior kidney are excretory in function .

Pathology

a) Glomerular nephritis

Here the Bowman’s capsule becomes thickened leading to decrease in filtration efficiency of kidney.

The epithelial layer will be sloughed off (detachment of epithelial layer) from the basement membrane and forms wide mass in the Bowman’s capsule which reduces the filtration efficiency. This may be happen due to some toxin produced by bacteria, virus and due to pollution.

b) Parasitic deposition (Pathology)

The pathology leads to deposition of glomerulus in the Bowman ’s capsule, which block the filtration capacity and finally damage the tissue. The parasitic deposition blocks the movement of the generated fluids in collecting ducts, etc.

2) Renal tubules

Renal cell tubules get damaged causing tubular necrosis. This is due to antibiotics like erythromycin, sulphamerazine which cause kidney problem.

a) Urolithiasis/Nephrocalcinosis

Formation of calciated stones in nephrons, nephric duct etc. This happes due to high CO₂ and a diet rich in calcium .

c) Interstitial fibrosis

This pathological change results due to proliferative kidney disease (PKDC). This may also be due to bacterial infection, leading to degradation of haemopoeitic tissue, haemopoeitic hyperplasia, vascular changes and diffused inflammation.

d) Tumour generation

Aflatoxin can generate tumour in liver.

F. Nervous System

The nervous system consist of brain, spinal cord, nerves and all other associated cell components.