Gills as morphological biomarkers in extensive and intensive rainbow trout (Oncorhynchus mykiss, Walbaum 1792) production technologies
Environ Monit Assess
Gills as morphological biomarkers in extensive and intensive rainbow trout (Oncorhynchus mykiss, Walbaum 1792) production technologies
Emilia Strzyżewska-Worotyńska 0 1
Józef Szarek 0 1
Izabella Babińska 0 1
Dominika Gulda 0 1
0 D. Gulda Department of Sheep, Goat and Fur Bearing Animal Breeding, University of Science and Technology , Mazowiecka St. 28, 85-084 Bydgoszcz , Poland
1 E. Strzyżewska-Worotyńska
We investigated environmental impacts on rainbow trout (Oncorhynchus mykiss) reared at fish farms with either extensive technology, in a flow-through system (FTS, n = 3), or intensive technology, in a recirculating aquaculture system (RAS, n = 3). All fish were fed the same rations. Fish were caught in spring and autumn (body mass, 501-750 g) from these six farms. We performed macroscopic (intact fish) and microscopic (gills stained with haematoxylin/eosin) examinations. Lesions were categorised based on the type and location of structural abnormalities. The histopathological index (HAI) was calculated, and each lesion was scored. Fish reared in FTS or RAS were compared for the prevalence of morphological lesions. Gill epithelial hypertrophy and hyperplasia comprised 73% (RAS) to 79% (FTS) of all morphological abnormalities. In spring and autumn, lesions comprised, respectively, 11 and 18% (FTS) and 16 and 10% (RAS) mucous and chloride cell abnormalities and 8 and 4% (FTS) and 10 and 3% (RAS) blood vessel abnormalities. Diffuse, irreversible gill lesions were observed sporadically in all fish. Gill epithelium received the most exposure to environmental pathogens. HAIs indicated that normal gill architecture and minor lesions predominated in all fish. However, among trout caught in spring, moderate and extensive changes in gills occurred more commonly with RAS (34%) than with FTS (17%). Trout caught in autumn displayed no great differences. These results indicated that FTS prepared fish better than RAS for wintering. Moreover, we showed that gills were an excellent biomarker for analysing the impact of extensive and intensive production environments on rainbow trout.
Biomarker; Gills; Morphological lesions; Rainbow trout; Fish production technology
Introduction
When applied in morphological investigations, biomarkers
are sensitive tools for the early detection of environmental
changes
(De la Torre et al. 2005; Heier et al. 2009;
Marcovecchio 2004; Rayment and Barry 2000)
.
Biomarkers demonstrate correlations between environmental
factors and their outcomes, and they provide insight into
both the status of an ecosystem and the status of a given
organism
(Flores-Lopes and Thomaz 2011;
FontainhasFernandes et al. 2008; Gernhofer et al. 2001; Maria et al.
2009; Sorour and Harbey 2012; Strzyżewska et al. 2015;
Velcheva 2002; Yancheva et al. 2015)
. Fish gills comprise
one of these biomarkers: the gill is a metabolically active
tissue involved in gaseous exchange, and it accumulates a
significant proportion of toxins
(Abrahamson et al.
2008; Andres et al. 2000; Benli and Ozkul 2008; Evans
et al. 2005; Marcovecchio 2004; Poleksic and
MitrovicTutundzic 1994; Strzyżewska et al. 2016; Thophon et al.
2003)
. Morphological lesions in the gills are easier to
detect than functional abnormalities
(Fanta et al. 2003;
Fernandes et al. 2007; Velasco-Santamarίa and
CruzCasallas 2008)
, because they may become visible long
before behavioural changes in fish can be detected
(Yancheva et al. 2015; Heier et al. 2009)
. Furthermore,
the gills serve as early warning signs on the health
status of fish
(Sorour 2001)
. It is believed that the
degree of morphological lesions in the gills can
delimit the degree of environmental pollution
(Camargo
and Martinez 2007; Flores-Lopes and Thomaz 2011;
Haaparanta et al. 1997; Ogundiran et al. 2009;
Thophon et al. 2003)
. Indeed, the concentration of
toxic factors in this organ is identical to the level of
xenobiotics found in the water that the fish inhabit. In
contrast, toxin concentrations in the other organs (such
as the liver or kidneys) depict only the degree of
distribution of the toxic compounds
(Andres et al.
2000; Kroglund et al. 2008; Manera et al. 2016)
.
Importantly, fish are exposed both to environmental
factors and to stress that results from manipulations,
bioengineering and hydrotechnical procedures that
occur during their production cycle
(Cruz-Casallas et al.
2011; Tello et al. 2010; Yancheva et al. 2015)
. Current
literature does not include any data from studies that
examined whether the gills may serve as a
morphological biomarker for evaluating fish production
technologies. This study aimed to decrease this gap, because they
discuss the pathomorphological aspects of rainbow trout
gills that are modulated by common production
systems, including the extensive flow-through system
(FTS) and the intensive recirculating aquaculture system
(RAS).
Materials and methods
This study was carried out over two seasons (autumn
and spring) (...truncated)