2.5
Excretory System
Salmon, like most fish, release their nitrogenous wastes
as ammonia and the gills play an important role by excreting this compound through diffusion into the surrounding water. However the core of the excretory system
remains in the kidney, with primary functions performed
by filtering wastes from the blood to maintain the body
fluid levels, collect and excrete the waste products and
maintain pH.
2.5.1 Kidney
The kidney comprises tightly fused units giving the appearance of a single organ. The kidney is located retroperitoneally along most of the length of the body cavity, ventral to
the vertebral column and dorsal to the swim bladder. The
anterior section, also known as the cranial or head kidney is
composed entirely of haematopoietic and lymphoid tissue
(Fig. 2.21), while the posterior section has the excretory role
and the functional unit are the nephrons (glomeruli and
tubules) embedded in haematopoietic tissue (Fig. 2.22).
The typical nephron of salmonids living in fresh water is
characterized by a relatively large glomerulus that fills up
the Bowman’s capsule (Fig. 2.23). From the latter, the renal
tubule begins with the short neck segment characterized by
low cuboidal epithelium with long cilia. This section is
divided into a first segment with eosinophilic, cuboidal to
columnar epithelium with a distinct brush border, and a
second segment with a taller columnar epithelia and a
centrally located oval nucleus. The latter has a prominent
brush border but lack the extensive tubular system in the
Fig. 2.21 Horizontal section of rainbow trout showing head kidney.
Note Y-shaped portion at cranial end
Fig. 2.22 Kidney tubules and interstitial tissue
Fig. 2.23 Glomerulus in the interstitial renal tissue of adult Atlantic
salmon
Fig. 2.20 Transverse section through Atlantic salmon parr showing
epidermis, scales, lateral line, red and white muscle. Low power
14
2 Functional Anatomy
Excretory System
Salmon, like most fish, release their nitrogenous wastes
as ammonia and the gills play an important role by excreting this compound through diffusion into the surrounding water. However the core of the excretory system
remains in the kidney, with primary functions performed
by filtering wastes from the blood to maintain the body
fluid levels, collect and excrete the waste products and
maintain pH.
2.5.1 Kidney
The kidney comprises tightly fused units giving the appearance of a single organ. The kidney is located retroperitoneally along most of the length of the body cavity, ventral to
the vertebral column and dorsal to the swim bladder. The
anterior section, also known as the cranial or head kidney is
composed entirely of haematopoietic and lymphoid tissue
(Fig. 2.21), while the posterior section has the excretory role
and the functional unit are the nephrons (glomeruli and
tubules) embedded in haematopoietic tissue (Fig. 2.22).
The typical nephron of salmonids living in fresh water is
characterized by a relatively large glomerulus that fills up
the Bowman’s capsule (Fig. 2.23). From the latter, the renal
tubule begins with the short neck segment characterized by
low cuboidal epithelium with long cilia. This section is
divided into a first segment with eosinophilic, cuboidal to
columnar epithelium with a distinct brush border, and a
second segment with a taller columnar epithelia and a
centrally located oval nucleus. The latter has a prominent
brush border but lack the extensive tubular system in the
Fig. 2.21 Horizontal section of rainbow trout showing head kidney.
Note Y-shaped portion at cranial end
Fig. 2.22 Kidney tubules and interstitial tissue
Fig. 2.23 Glomerulus in the interstitial renal tissue of adult Atlantic
salmon
Fig. 2.20 Transverse section through Atlantic salmon parr showing
epidermis, scales, lateral line, red and white muscle. Low power
14
2 Functional Anatomy