Aquaculture
ELSEVIER
Aquaculture 158 ( 1997) 167- I77
Spontaneous steatitis of epicardial fat in farmed
white sturgeon (Acipenser transmontanus)
Franc0 Guarda a, Gianluca Bertoja a, Ivo Zoccarato
Enzo Tartari b, Bartolomeo Biolatti ’
b,*,
a Dipartimento di Patologia Animale, Via Nizza 52, 10126 Torino, Italy
b Dipartimento di Scienze Zootecniche, oia L. da Vinci 44, 10095 Grugliasco, Torino, Italy
’ Istituto di Patologia e Igiene Veterinaria, Agripolis, Legnaro, Padoua, Italy
Accepted 17 June 1997
Abstract
The hearts of 235 white sturgeons originating from an intensive farm system were examined in
detail. Skin, muscle and abdominal viscera did not show any pathological features, except for the
presence of liver and epicardial fat. All sturgeons had high levels of epicardial fat and 70%
showed important variations in colouration,
which was from grey/brownish
to blackish.
Histopathological
examination revealed lymphocyte infiltrates, around the blood vessels as small
focal lesions near the intercellular spaces, or as thin strips along the borders of fat tissue. In severe
cases, heavy lymphoid infiltrates and proliferative lesions were evident and fatty tissue was
replaced by inflammatory
and proliferative
tissue. The underlying myocardium
was rarely
affected. A diagnosis of infiltrative and proliferative steatitis is postulated. Moreover, a high
percentage of the livers showed steatosis. Aetiology is still unknown, but the authors envisage a
nutritional imbalance linked with oxidised fat intake. 0 1997 Elsevier Science B.V.
Keywords:
Sturgeon;
Acipenser
transmontanus;
Epicardial
fat steatitis; Oxidised
fat
1. Introduction
One of the most exciting
farming.
For
a long
time
facets of recent years
sturgeon
cultivation
in fish farming
was conducted
is intensive
sturgeon
just for restocking
purposes, particularly in Russia (Huet, 1986). Recently, the request for a fresh product,
consumed in slices or as smoked fillets, has increased in Europe and Italy. In 1993, the
* Corresponding
author. Tel. + 39-1 I-6708568;
fax: +39-l
l-6708563.
0044-8486/97/$17.00
0 1997 Elsevier Science B.V. All rights reserved
PII SOO44-8486(97)0016
I-O
F. Guarda et al./Aquaculture
168
Table 1
Proximate
analysis
158 (1997) 167-177
of diet (% of wet weight) (mean k s.d.)
6.95 + 0.10
9.43 * 0.02
47.34+ 1.74
14.54kO.17
113 mg/lOO g
from 7.2 to 56 meq/kg
< 0.1 mg/kg
Moisture
Ash
Crude protein
Ether extract
Vitamin E (as cY-tocopherol)
Peroxide value
Selenium
of fat
Italian production of sturgeon exceeded 300 tons, i.e., about 60% of the European
production (FAO, 1995). The main species reared as food fish in Italy and elsewhere in
the world (Hung, 1991; Arlati and Bronzi, 1994) is the Pacific white sturgeon ( Acipenser
transmontanus).
Fig. 1. Formalin-fixed
normal heart of white sturgeon.
F. Guarda et al./Aquaculture
158 (1997) 167-177
Fig. 2. Sections of formalin-fixed
169
normal heart.
Fig. 3. Different formalin-fixed hearts: the first on the right show a normal appearance,
show progressive levels of alteration.
whereas the other three
In spite of a promising market, the information about the nutrient requirements of
sturgeon is scarce. In the last ten years the interest of research investigation has been
focused just on juvenile nutrition. For this reason, suitable commercial diets formulated
expressly for the growing sturgeon are still unavailable. As reported by Hung (1991) in
practice, sturgeons are fed using salmonid feeds. This lack of information is considered
170
F. Guarda et al./Aquaculture
Fig. 4. Gross appearance
of formalin-fixed
158 (1997) 167-177
heart showing focal lesions on epicardial
fat.
the major limiting factor of sturgeon farming development. In fact, prolonged feeding by
inadequate diets can induce metabolic changes and poor growth (Hung, 1991). In the
same way, the information available in sturgeon pathology is very scarce and non-existent in nutritional pathology, as it appears by the examination of nutritive pathology
references (Tacon, 1992). The aim of this report is to describe, from the anatomo-histopathological point of view, the epicardial fat steatitis spontaneously observed in farmed
white sturgeon in Northern Italy.
2. Material and methods
235 white sturgeons (A. transmontanus),
four or five year olds from an intensive
farm system in Northern Italy, were commercially slaughtered at 4/5 kg body weight.
The sturgeons had been kept in earth ponds, supplied by well water heated (18-20°C) by
an exchange heat-system
from a steel plant. The fish were fed l-1.5%
of body
weight/day
with a commercial diet for trout. The approximate composition of this diet
is reported in Table 1. The diet composition is sufficiently constant over the entire
growing cycle and was analysed for its fatty acid profile, vitamin E, selenium and
F. Guarda et al./Aquaculture
Fig. 5. Gross appearance
of formalin-fixed
peroxide values (AOAC, 1990). In order to
slaughter, different organs were sampled.
malin. Successive, representative
sections
embedded in paraffin, sectioned (approx.
Eosin (HE).
158 (1997) 167-177
heart showing fat completely
171
blackish.
provide possible pathological evidence at the
The hearts were fixed in 10% buffered-for(apex, middle and base) of the hearts were
4 pm> and stained with Hematoxylin
and
3. Results and discussion
Visual examination of the skin and muscle did not show any pathological changes,
whereas all fish showed to some extent severe fatty liver. Fat altered liver is very
common in farmed fish (Roberts and Bullock, 1989), and such a case does not seem to
affect their growth (Hung, 1991). Seventy percent of the sturgeons showed a normal
quantity of epicardial fat (Fig. 1 and Fig. 2) but variations in colour from grey/brownish
172
F. Guarda et al. / Aquaculture I58 (1997) 167-I 77
Fig. 6. Histological
section of heart whit initial lesions of epicardial
fat steatitis (HE, X 70).
to blackish were evident (Fig. 3). Colour alterations were focal in the lightly affected
organs (Fig. 4) or evenly distributed in the severely affected hearts (Fig. 5).
Histopathological
examination revealed lymphocyte infiltrates, either perivascular as
small focal lesions near the intercellular spaces (Fig. 6) or as thin strips along the border
of fatty tissue (Fig. 7 and Fig. 8). In severe cases, heavy lymphoid infiltratives and
proliferative lesions were evident; fat was replaced by inflammatory
and proliferative
tissue; the underlying myocardium was rarely affected (Fig. 9). Some adipocytes showed
necrotic cytoplasm with monocyte invasion (Fig. 10).
The typical lesions resulting from selenium and/or vitamin E deficiency observed in
muscle tissue and the yellowish serous fluid contained in the body cavity of Atlantic
salmon (Poston et al., 1976) and in rainbow trout (Bell et al., 1985) were not evident.
A diagnosis of infiltrative and proliferative steatitis has been postulated. Macroscopic
and histological
appearance characterised
by a specific condition of epicardial fat
steatitis has not been reported in other farmed sturgeons. Pathological alterations due to
nutritional imbalances are often characterised by epicarditis which is a common disease
in farmed trout (Guarda et al., 1995) as well as in tilapia (Soliman et al., 1983). In
tilapia the alterations could be due to the intake of oxidised fat. Fat oxidation is one of
the most important deteriorations
of feed and plays an important role to induce
metabolic changes that could be at the basis of different diseases, among these the fat
steatitis.
Diet analysis did not show any evidence of vitamin E, selenium and fatty acid
deficiency relative to trout requirements.
However, the peroxide value showed high
variability
in different samples ranging between a minimum of 7 meq/kg
and a
F. Guarda et al./Aquaculture
Fig. 7. Histological appearance of ample inflammatory
appear yet normal (HE, X 1.50).
158 (1997) I67-I77
lesions of epicardial
173
fat. Some part of adipose tissues
maximum of 56 meq/kg.
We can speculate that the amount of vitamin E and other
antioxidant agent as butylated hydroxytoluene
(BHT) might not be able to prevent fat
diet oxidation if diets are high in fish oil content. In fact, the diets used for the fish in
this study contained high levels of unsaturated fatty acids (UFA) (Table 2). Moreover, it
is worth mentioning that high contents of unsaturated fatty acids in carp and trout diets
induce an increase of requirement in vitamin E (Watanabe et al., 1981; Cowey et al.,
1983) which could also occur for sturgeon.
Considering that the farming cycle of sturgeon is extended, it is supposed that fish
often intake diets containing oxidised fat. In fact, the correct conservation
of diets
elevated in fish oil points to a serious problem due to variabilities
in air and light
exposure, feed processing, temperature of storage. Gonzalez et al. (1992) showed that
the peroxide value of diets containing high levels of fish oil increased rapidly (72 h) in
spite of the addition of antioxidant agents.
174
F. Guarda et al./Aquaculture
Fig. 8. Appearance
Fig. 9. Histopathological
(HE, x 150).
of epicardial
appearance
158 (1997) 167-177
fat steatitis in cross section of heart (HE, X 150).
of substitution
of fat by inflammatory
reaction
and proliferative
tissue
F. Guarda et al./Aquaculture
Fig. 10. Necrotic cytoplasm
158 (1997) 167-177
with monocytes
175
invasion (HE, x 250).
In this study, the pathological alterations described neither reduce the productive
traits nor increase mortality. In our opinion, the epicardial fat lesion observed indicated a
sub-clinical
pathological
condition. All the investigated
hearts were removed from
apparently healthy sturgeons routinely slaughtered for human consumption.
Table 2
Fatty acids composition
of diet (% of total fatty acids identified)
14:o
16:O
16:l w7
18:O
18:lw9
18:2w6
18:3w3
20: 1
20:5w3
22:503
22~6~3
Others
S saturated”
Z monounsaturatedh
2 polyunsaturated”
“Sum of 12:O: 14:O; 16:O; 18:O 20:0 and 22:0.
hSum of 14:l; 16:l; 17:l; 2O:l; 22:l; 24:l plus 18:3
‘Sum of 18:2; 20:5; 22:2; 22:4; 22:5 and 22:6.
(mean f s.d.)
7.6 + 0.38
17.3 i 0.84
7.1 kO.59
3.6kO.32
12.6t0.73
3.4 f 0.64
0.8iO.11
0.9+0.14
16.4, 1.02
2.2k0.16
9.0+0.81
11.0_+0.91
31.8*2.08
23.1+ 1.53
34.9 f 2.5 1
176
F. Guarda et al./Aquaculture
158 (1997) 167-177
At present, the cause and pathogenesis of the fat lesions is still unknown. However,
according to the literature, we can suppose that epicardial fat steatitis could be a specific
lesion due to unavailability
of vitamin E or insufficient
antioxidant protection. This
could be similar to the pansteatitis described in rainbow trout (Roberts et al., 1979). In
their study, they observed inflammatory
cellular infiltration
of lipid tissue in the
swimbladder, abdominal and peripancreatic fat.
Our supposition
is supported by the fact that among the terrestrial mammals,
especially cats and other carnivors, it is well known that the yellow fat disease is due to
the intake of diets containing large amounts of unsaturated fatty acid and deficient in
vitamin E (Scott, 1980).
In our opinion, the aetiology of the lesions is likely to be nutritional, since only the
epicardial fat storage of sturgeon is altered, whereas the other organs, excluding the
liver, do not show obvious changes. At present, we did not find a significant relationship
between liver steatosis and epicardial fat steatitis. However, there is an indication from
the literature that confirms the hepatotoxic effect of oxidised fats (Roberts and Bullock,
1989). Liver ceroid degeneration
accompanied
by other lesions, was observed in
chinook salmon (Fowler and Banks, 1969) in catfish (Murai and Andrews, 1974) and in
rainbow trout (Moccia et al., 1984) fed diets containing oxidised fish oil.
In conclusion, even if the epicardium is a common site for lesions associated with
parasites or pathogens due to the lymph drainage into the pericardial sac, the lack of
damage on the myocardium itself leads us to suspect a pathology of nutritional origin.
Acknowledgements
We wish to thank the staff of Agroittica Lombarda (Calvisano, Brescia, Italy) for
providing the materials. Partial financial support for this research was provided by the
Italian Ministry of University and Research (MURST 40%) as part of the program
‘Tecnologie avanzate nell’allevamento
delle piccole specie’.
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