PATHOLOGICAL ASPECTS OF INTENSIVE REARING

Mr G. GIORGETTI

Please excuse me for not being able to speak to you in french, this language being more familiar to you. Many thanks for your kind invitation. I will try to resolve this language problem by employing tables and slides.

Health, a well accepted factor, desively conditions the economic results of the zootechnical interests; this applies for all intensive rearings, and more specifically fishculture (table 1). It is clearly known that the environment is a fundamental factor for the pathological phenomenon to arise. and develop. Environment taken as a stress factor; means the effort made by the animal to adjust to an environmental situation which is not truly appropriate.

When one enters into a cattle shed or pig sty one can sense immediatly if something is wrong (too hot, ammonia, etc… ) but in a fish farm, where the environment is water, no abnormalities are remarked although there may exist a bad environmental situation (Tab. 2–3–4–5).

The sanitary situation is very important, and will become more important, for at least three reasons, given here under :

1. The objectives of the Management techniques are to increase the amount of products per unit of space. This means a greater concentration of animals; and therefore greater risks of infection;

2. The present environmental situation leads us to believe that the environment is becoming worse rathan than better.

3. At present, genetics in fishculture do not concern health problems but only the conversion and growth rates of the fish, delayed or advanced laying, etc… This caused the fish being weaker and more sensitive to the pathological agents.

Sudden mortality, decreasing progressively, is generally linked with environmental situations while mortality which increase progressively is generally linked with disease.

To make a diagnoses, the 3 different sources of information here following must be employed :

- anamnesis,

- inspection,

- clinic.

Anamnesis

A new disease is clearly remarked when the mortality rises and the food consumption decreases. Inspection will permit us to notice that the fish show abnormal behaviour in the tanks, the fish are found on the bottom or edges of the tanks, so avoiding being carried by the stream flow. The fish will show an abnormal reaction to stimuli. Two non-specific lesions are remarked when the clinical test is performed, the fish are suffering and the lesion degree can vary in relation to the disease: exophthalmus and hyperpigmentation.

Disease can be caused by :

- Virus,

- bacteria,

- parasite,

- Mycetes

- Environment.

and for each of these catagories the therapy and prophylaxis must be mentioned.

Virus

(Slides). No therapy, no prophylaxis as active immunisation, only prophylaxis plan possible (Table 6, 7).

Bacteria

(Slides). The Italian Ministerial Ordonance of 4 August 1969 regulates the use of chemiotheraphic and antibiotic drugs to be mixed with feed, against bacterial disease. (Tab. 8 and 9). Today vaccines are employed for prophylaxis (Tab. 10, 11, 12, 13, 14, and 15).

Parasites

(Slides). The prophylaxis and theraphy employed for parasitic disease are based on the appropriate use of disinfectants, as seen in table 10.

Mycetes

These can be generally considered as negative elements of secondary irruption in a pathological process. Disinfectants shall be employed as therapy.

Environment

(Slides). It is always responsable for the evolution of pathological events, as already seen, but sometimes it is the sole cause of disease, as in the case of the well known “gas bubble disease” (acute and chronic) and in “gill disease”. The prophylaxis and therapy possible is to eliminate the cause which has defined the pathological phenomenon.

TABLE 1

TROUT PRODUCTION IN WESTERN EUROPE

(Metric tons)

Table 2     Interaction of factors necessary at the development of the disease in aquaculture

Table 3

Sometimes an aetiological agent is conditioned by another (erytrodermatytes of the carp condition by the virus)

Table 4

Biological, chemical, physical and procedural environmental factors which can adversely impact fish in intensive culture and cause stress.

Table 5 A

Table 5 B

Table 6

VIRAL HAEMORRHAGIC SEPTICEMIA COST

VHS killes fries and fingerlings which cost more than market size trout.

Table 7

Official prophylaxis plane against viral haemorrhagic septicemia (VHS) in Province of TRENTO.

Table 8

Tab. 2. Test of sensitivness to antibiotics

Table 9

Therapy and Disinfection table

(1) Italian Ministerial Ordinance 4 August 1969

(2) Pay attention to the water temperature: The higher is, the need of the disinfectant concentration (till 10 %, 250 p.p.m, between 10 % – 15 %, 200 p.p.m, over 15 %, 150 p.p.m).

Table 10

VACCINE

ADMINISTRATION METHODS

Table 11

FACTORS WHICH INFLUENCE THE IMMUNITARY LEVEL IN VACCINATED FISH

Table 12

VIBRIO VACCINE EXPERIMENT

Table 1 (1° Experiment without hyper-osmotic solution)

Table 2 (2° Experiment with hyper-osmotic solution)

Table 3 (Experiment in feild with inactived vaccine with formalin without pre-vaccinal hyper-osmotic bath

Table 13

Table 14

Table 15

% Pathological events in farmed sea-bass (Dicentrarchus labrax)

Vaccination trials of Sea-bass fry

Infection test with Vibrio anguillarum (30' in 10 1 of water with 28 × 10⁷ cell/ml)

MORTALITY