Idiopathic Diseases
11
Abstract
Diseases with uncertain or compound aetiology occur in fish farming and defined as those
where the aetiology is unknown, or idiopathic. However, this may be difficult to ascertain
and furthermore many different conditions may occur concurrently with more well-defined
diseases, such as those with an infectious aetiology. It is characteristic for many idiopathic
diseases that they may not be lethal themselves, but when they affect an immunocompromised fish or occur with other agents, they may cause clinical disease and
associated mortality. Similarly, the transition between production-related disease and
infectious disease can be obscure.
Keywords
Idiopathic Salmon Trout
As with almost any farmed species, diseases with uncertain
or compound aetiology also occur in fish farming and for
the purpose of this book idiopathic diseases are those
conditions where the aetiology is unknown. In some
cases, these conditions are the result of different types of
manipulations of the fish, the feed and the environmental
factors in order to optimise the production and increase
profitability. Due to the complexity, their aetiology may
be difficult to ascertain and furthermore, many different
conditions occur concurrently with more well-defined diseases, e.g. those of infectious aetiology. It is characteristic
for many idiopathic diseases that they may not be lethal
themselves, but when occurring together with other agents or
in immunocompromised fish, they may cause clinical disease
and mortality. For example, fish with shortened opercula,
frayed fins or cardiac diseases, can cope with normal farming
practices well, but are typically among the first to succumb
during stressful events like crowding, treatments, suboptimal
environment and outbreak of infectious diseases. The transition between production-related disease and infectious disease
can also be obscure. Certain conditions such as skeletal
malformations or metabolic disorders/dysfunctions are representatives of emerging or production disease and some
examples of them (cardiac lesions, nutrition and deformities)
are covered in other sections of this book. Selected idiopathic
diseases are discussed below.
11.1 Ulcerative Dermal Necrosis
Losses in native Atlantic salmon and sea trout in Britain
were the subject of investigation by an early fishery research
project during the late 1800s and early 1900s. This work was
carried out in Scotland into the so called ‘Salmon disease’,
which is referred to as ulcerative dermal necrosis (UDN).
Although many thousands of salmon died and the apparent
spread between watersheds indicated an infectious cause, to
date there has been no definitive agent identified. Furthermore, there are no records of UDN from farmed fish.
UDN is a chronic dermatological condition described from
adult Atlantic salmon and brown trout returning to fresh
water. Signs include small superficial grey-coloured head
lesions above the eye, along the snout or adipose fin, often
with erosion on the cranium, to deeper ulcers involving large
areas principally on the top of the head (Figs. 11.1 and 11.2).
In the latter stages, infection with Saprolegnia parasitica is
frequently associated with the open wounds. In addition there
D.W. Bruno et al., A Colour Atlas of Salmonid Diseases,
DOI 10.1007/978-94-007-2010-7_11, # Springer Science+Business Media B.V. 2013
179
11
Abstract
Diseases with uncertain or compound aetiology occur in fish farming and defined as those
where the aetiology is unknown, or idiopathic. However, this may be difficult to ascertain
and furthermore many different conditions may occur concurrently with more well-defined
diseases, such as those with an infectious aetiology. It is characteristic for many idiopathic
diseases that they may not be lethal themselves, but when they affect an immunocompromised fish or occur with other agents, they may cause clinical disease and
associated mortality. Similarly, the transition between production-related disease and
infectious disease can be obscure.
Keywords
Idiopathic Salmon Trout
As with almost any farmed species, diseases with uncertain
or compound aetiology also occur in fish farming and for
the purpose of this book idiopathic diseases are those
conditions where the aetiology is unknown. In some
cases, these conditions are the result of different types of
manipulations of the fish, the feed and the environmental
factors in order to optimise the production and increase
profitability. Due to the complexity, their aetiology may
be difficult to ascertain and furthermore, many different
conditions occur concurrently with more well-defined diseases, e.g. those of infectious aetiology. It is characteristic
for many idiopathic diseases that they may not be lethal
themselves, but when occurring together with other agents or
in immunocompromised fish, they may cause clinical disease
and mortality. For example, fish with shortened opercula,
frayed fins or cardiac diseases, can cope with normal farming
practices well, but are typically among the first to succumb
during stressful events like crowding, treatments, suboptimal
environment and outbreak of infectious diseases. The transition between production-related disease and infectious disease
can also be obscure. Certain conditions such as skeletal
malformations or metabolic disorders/dysfunctions are representatives of emerging or production disease and some
examples of them (cardiac lesions, nutrition and deformities)
are covered in other sections of this book. Selected idiopathic
diseases are discussed below.
11.1 Ulcerative Dermal Necrosis
Losses in native Atlantic salmon and sea trout in Britain
were the subject of investigation by an early fishery research
project during the late 1800s and early 1900s. This work was
carried out in Scotland into the so called ‘Salmon disease’,
which is referred to as ulcerative dermal necrosis (UDN).
Although many thousands of salmon died and the apparent
spread between watersheds indicated an infectious cause, to
date there has been no definitive agent identified. Furthermore, there are no records of UDN from farmed fish.
UDN is a chronic dermatological condition described from
adult Atlantic salmon and brown trout returning to fresh
water. Signs include small superficial grey-coloured head
lesions above the eye, along the snout or adipose fin, often
with erosion on the cranium, to deeper ulcers involving large
areas principally on the top of the head (Figs. 11.1 and 11.2).
In the latter stages, infection with Saprolegnia parasitica is
frequently associated with the open wounds. In addition there
D.W. Bruno et al., A Colour Atlas of Salmonid Diseases,
DOI 10.1007/978-94-007-2010-7_11, # Springer Science+Business Media B.V. 2013
179