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(a) Anterior hemibranch of the third gill arch from a 68-kg striped marlin, Kajikia audax, showing the division of 425 filaments into 10 bins of 40 and one bin of 25 (indicated by dotted white lines). The middle filament from each bin has been removed for measurements of lamellar frequency and bilateral surface area. (b) Scanning electron microscope (SEM) image of a selected gill filament used for determination of lamellar frequency. (c) SEM image of a corrosion-cast striped marlin lamella removed for determination of the bilateral surface area.
Source publication
Respiration in most fishes involves gas exchange between the water and blood through the gill epithelium. The ability to acquire oxygen to sustain metabolic processes depends largely on the gill respiratory surface area and the thickness of the water-blood barrier. Measurement of these dimensions requires lengthy and exacting methodologies, but all...
Contexts in source publication
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... and Animal Respiration | Gill Respiratory Morphometrics 805 and, depending on their abundance, dividing them into calculated and these amounts are summed to estimate bins of 10, 20, or more on each arch (Figure 2(a)). The the total filament length for the gills on one side of the middle filament from each bin is measured and assumed head. ...
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... measure ments of each dimension are typically determined along the length of each filament to account for variation in lamellar shape, size, and spacing. For lamellar frequency, the filament is typically dissected from the arch (Figure 2(a)) and photographed under magnification near its base, middle, and tip (Figure 2(b)). Lamellae from these same locations are then dissected from the filament, mounted flat, and photographed to measure lamellar bilateral area (Figure 2(c)). ...
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... measure ments of each dimension are typically determined along the length of each filament to account for variation in lamellar shape, size, and spacing. For lamellar frequency, the filament is typically dissected from the arch (Figure 2(a)) and photographed under magnification near its base, middle, and tip (Figure 2(b)). Lamellae from these same locations are then dissected from the filament, mounted flat, and photographed to measure lamellar bilateral area (Figure 2(c)). ...
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... lamellar frequency, the filament is typically dissected from the arch (Figure 2(a)) and photographed under magnification near its base, middle, and tip (Figure 2(b)). Lamellae from these same locations are then dissected from the filament, mounted flat, and photographed to measure lamellar bilateral area (Figure 2(c)). Lamellar frequency and area measurements from each bin are weighted according to the filament length of that bin before being averaged (thus ensuring lamellar measurements from a bin with a longer filament length will contribute propor tionately more toward the mean for the entire gills). ...
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... tunas and other fast-swimming oceanic teleosts, large gill areas generally result from numerous and long gill filaments with high lamellar frequencies (>30 mm �1 in some species). The increased number of filaments is achieved through changes to lamellar design, from a semicircular or triangular shape, typical of most fishes (Figure 3(a)), to a long, rectangular contour with a low profile (height) (Figures 2(c) and 3(b)), thus allowing filaments to be closely spaced (Figure 3(b)). This shaping also allows for a marked reduction in the thickness of the water-blood barrier (i.e., low-profile lamellae require less structural support than tall lamellae) contributing to gen erally thin lamellae (only 5-6 mm in scombrids and billfishes). ...
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Squids are thought to obtain a large portion of their oxygen via simple diffusion across the skin in addition to uptake at the gills. Although this hypothesis has support from indirect evidence and is widely accepted, no empirical examinations have been conducted to assess the validity of this hypothesis. In this study, we examined cutaneous respir...
Citations
... where L fil is the total length (mm) of all gill filaments on both sides of the head, n lam is the lamellar frequency (i.e. the mean number of lamellae per unit length on one side of a filament, multiplied by two to account for lamellae on both sides of the filament) and A lam is the mean bilateral surface area of a lamellae (Wegner, 2011;Wegner et al., 2010). ...
... A magnified photo (Amscope SM-1 Series, Irvine, CA, USA) was taken of the median filament in each bin, which was assumed to be representative of all filaments in that bin. The length of this median filament was traced and measured using imaging software (ImageJ, National Institutes of Health, Bethesda, MD, USA, Java 1.8.0_172) following methods detailed in Wegner et al. (2010) and Wegner (2011). The total length of all filaments (L fil ) on all hemibranchs on the right side of the head was calculated by multiplying the length of the median filament in each bin by the total number of filaments in that bin, then summing the length of all filaments in all bins. ...
... Following filament measurements, lamellar frequency and lamellar surface area measurements were made on all median filaments from all eight hemibranchs on the first dissected brook trout individual. These measurements showed that the posterior hemibranch on the second gill arch was most representative of the gills as a whole, and thus for subsequent brook trout individuals, lamellar frequency and mean lamellar surface area measurements were based solely on this hemibranch (Wegner, 2011;Wegner et al., 2010). To make lamellar frequency and lamellar surface measurements, the median filament from each bin was viewed under the dissection scope. ...
Declining body size in fishes and other aquatic ectotherms associated with anthropogenic climate warming has significant implications for future fisheries yields, stock assessments and aquatic ecosystem stability. One proposed mechanism seeking to explain such body-size reductions, known as the gill oxygen limitation (GOL) hypothesis, has recently been used to model future impacts of climate warming on fisheries but has not been robustly empirically tested. We used brook trout (Salvelinus fontinalis), a fast-growing, cold-water salmonid species of broad economic, conservation and ecological value, to examine the GOL hypothesis in a long-term experiment quantifying effects of temperature on growth, resting metabolic rate (RMR), maximum metabolic rate (MMR) and gill surface area (GSA). Despite significantly reduced growth and body size at an elevated temperature, allometric slopes of GSA were not significantly different than 1.0 and were above those for RMR and MMR at both temperature treatments (15°C and 20°C), contrary to GOL expectations. We also found that the effect of temperature on RMR was time-dependent, contradicting the prediction that heightened temperatures increase metabolic rates and reinforcing the importance of longer-term exposures (e.g. >6 months) to fully understand the influence of acclimation on temperature–metabolic rate relationships. Our results indicate that although oxygen limitation may be important in some aspects of temperature–body size relationships and constraints on metabolic supply may contribute to reduced growth in some cases, it is unlikely that GOL is a universal mechanism explaining temperature–body size relationships in aquatic ectotherms. We suggest future research focus on alternative mechanisms underlying temperature–body size relationships, and that projections of climate change impacts on fisheries yields using models based on GOL assumptions be interpreted with caution.
... Gill slits are external openings of the parabranchial cavity in sharks and rays (Elasmobranchii) where exhalent oxygen-depleted water exits the body (Wegner 2015). The structure of the gill slit arises from the extension of interbranchial septum, which supports the gill filaments and surface area where oxygen uptake occurs (Wegner 2011(Wegner , 2015. Thus, there is a direct functional morphological connection between the height of the external gill slit length and the corresponding internal gill surface area: shark gill slit height is related to gill surface areas such that species with larger gill surface area have longer mean gill slit heights (VanderWright et al. 2020). ...
Morphology that is linked to metabolic rate - metabolic morphology - provides broad comparative insights into the physiological performance and ecological function of species. However, some metabolic morphological traits, such as gill surface area, require costly and lethal sampling. Measurements from anatomically-accurate drawings, such as those in field guides, offer the opportunity to understand physiological and ecological relationships without the need for physical, lethal sampling. Here, we assess the relationship between the metabolic physiology and ecology of nearly all extant sharks. Specifically, we examine the relationship between gill slit height and each of the three traits that comprise ecological lifestyle: activity, maximum size, and depth. We find that gill slit heights are positively related to activity (measured by the aspect ratio of the caudal fin) and maximum size but negatively related to depth. We also show that gill slit height is best explained by the suite of ecological lifestyle traits rather than any single trait. These results suggest that more active, larger, and shallower species have higher metabolic demands and that these greater metabolic demands can be estimated from external morphological and ecological traits. Our work demonstrates that meaningful ecophysiological relationships can be revealed through measurable metabolic morphological traits from anatomically-accurate drawings.
... The GOLT perspective that gill surface area limits metabolic rate is in direct contradiction to the widely accepted physiological view that gill surface area is adapted to match metabolic demand over a range of body sizes (Lefevre et al., 2017(Lefevre et al., , 2018. Although gills are indeed a surface, that surface is highly folded to increase the area available for gas exchange and gill surface area can indeed scale close to b=1.0 if required by metabolic demand (Wegner, 2011;Lefevre et al., 2017Lefevre et al., , 2018Wegner and Farrell, 2023). Although gill surface area does generally scale less than b=1.0 as predicted by geometric isometry and the GOLT, there are robust datasets showing species-specific scaling of gill surface area close to or even exceeding b=1.0, which would argue against the GOLT (Holeton, 1976;Wegner et al., 2010a;Bigman et al., 2018). ...
... where L fil is the total length of all gill filaments on both sides of the head, n lam is the lamellar frequency (i.e. the mean number of lamellae per unit length on one side of a filament, multiplied by two to account for lamellae on both sides of the filament), and A lam is the mean bilateral surface area of a lamella (Wegner, 2011(Wegner, , 2016. To determine these dimensions, we removed all five gill arches from the right side of the head and counted all filaments on all nine hemibranchs. ...
... We measured lamellar frequency and surface area on all median filaments from all nine hemibranchs on one side of the head on the first dissected individual. These measurements showed that the posterior hemibranch on the second gill arch was most representative of the gills as a whole, and thus for subsequent sharks, we based lamellar frequency and mean lamellar surface area measurements solely on this hemibranch (Wegner, 2011). ...
The gill surface area of aquatic ectotherms is thought to be closely linked to the ontogenetic scaling of metabolic rate, a relationship that is often used to explain and predict ecological patterns across species. However, there are surprisingly few within-species tests of whether metabolic rate and gill area scale similarly. We examined the relationship between oxygen supply (gill area) and demand (metabolic rate) by making paired estimates of gill area with resting and maximum metabolic rates across ontogeny in the relatively inactive California Horn Shark, Heterodontus francisci. We found that the allometric slope of resting metabolic rate was 0.966±0.058 95% CI, while that of maximum metabolic rate was somewhat steeper (1.073±0.040). We also discovered that the scaling of gill area shifted with ontogeny: the allometric slope of gill area was shallower in individuals <0.203 kg body mass (0.564±0.261), but increased to 1.012±0.113 later in life. This appears to reflect changes in demand for gill-oxygen uptake during egg case development and immediately post hatch, while for most of ontogeny, gill area scales in between that of resting and maximum metabolic rate. These relationships differ from predictions of the Gill Oxygen Limitation Theory, which argues that the allometric scaling of gill area constrains metabolic processes. Thus, for the California Horn Shark, metabolic rate does not appear limited by theoretical surface area-to-volume ratio constraints of gill area. These results highlight the importance of data from paired and size-matched individuals when comparing physiological scaling relationships.
... The classical physiological view is that the surface area of respiratory organs evolves to provide the capacity needed to meet an organism's requirements, instead of (aerobic) metabolic rate being driven by, and ultimately, limited by the surface area of the gills (Lefevre et al., 2017(Lefevre et al., , 2018Marshall & White, 2019a, 2019b. Relatedly, physiologists have noted that the surface area of gills are folded surfaces and thus are not under the same strict geometric constraints as seen in spherical or cubic objects (i.e. the scaling of gill surface area and body mass can and does deviate from theoretical surface area-to-volume ratios; Bigman et al., 2018;Lefevre et al., 2017Lefevre et al., , 2021Wegner, 2011). ...
... The growth of 'aquacultured' species is known to differ from that of wild fishes (due to food ad libitum, reduced predation and possibly increased aeration of aquaculture ponds; Pauly, 2010). Also, fishes that breathe air (either by possessing an air-breathing organ or passive oxygen diffusion through the skin) often have a lower gill surface area for a given body size compared to their non-air-breathing counterparts (Wegner, 2011). Thus, we created two subsets of our full data set to exclude species traditionally used in aquaculture and those capable of air-breathing. ...
... It is no surprise that activity explains variation in life history as activity is intertwined with life history traits (e.g. body size and growth), habitat and even gill surface area (Bigman et al., 2018;Gray, 1954;Hughes, 1984;Wegner, 2011). ...
Life history theory suggests that maximum size and growth evolve to maximize fitness. In contrast, the Gill Oxygen Limitation Theory (GOLT) suggests that growth and maximum size in fishes and other aquatic, water‐breathing organisms is constrained by the body mass‐scaling of gill surface area. Here, we use new data and a novel phylogenetic Bayesian multilevel modelling framework to test this idea by asking the three questions posed by the GOLT regarding maximum size, growth and gills. Across fishes, we ask whether the body mass‐scaling of gill surface area explains (1) variation in the von Bertalanffy growth coefficient ( k ) above and beyond that explained by asymptomatic size ( W ∞ ), (2) variation in growth performance (a trait that integrates the tradeoff between k and W ∞ ) and (3) more variation in growth performance compared to activity (as approximated by caudal fin aspect ratio). Overall, we find that there is only a weak relationship among maximum size, growth and gill surface area across species. Indeed, the body mass‐scaling of gill surface area does not explain much variation in k (especially for those species that reach the same W ∞ ) or growth performance. Activity explained three to five times more variation in growth performance compared to gill surface area. Our results suggest that in fishes, gill surface area is not the only factor that explains variation in maximum size and growth, and that other covariates (e.g. activity) are likely important in understanding how growth, maximum size and other life history traits vary across species.
... However, gill area index is not estimated from a regression relationship but calculated as G/W d , where G = an estimate of a species-specific mean gill surface area, W = mean body mass estimate associated with the mean gill surface area estimate, and d is a scaling parameter that would ideally be the species-specific ontogenetic slope of the relationship between body mass and gill surface area (Pauly, 1981(Pauly, , 2010. The parameter d is included because gill surface area largely scales disproportionately with body mass (i.e. usually <1), such that the ratio of gill surface area to body mass for a single individual changes throughout its lifetime (and thus is why a mean, relative [gill surface area at a given body mass or that predicted from a regression equation at a specific body mass], or mass-specific [gill surface area per gram of body mass] is not an ideal metric of gill surface area; Bigman et al., 2018;De Jager & Dekkers, 1975;Palzenberger & Pohla, 1992;Wegner, 2011). To calculate gill area index (G/W d ), Pauly (1981) used a compilation from Hughes and Morgan (1973) that reported mean estimates of gill surface area and body mass data measured from a random sample of individuals for a given species (Table S1). ...
... Later, Pauly (2010) estimated gill area index using a constant value of d for all species, d = 0.8, instead of predicting it based on a species' maximum body mass. Hence, the gill area indices originally used by Pauly (1981) and Pauly (2010) were likely biased by the sizes at which gills were measured (i.e. the sizes used to generate the species' means), the prediction of the parameter d and the assumption that the slope of gill surface area was constant across a broad array of species (an assumption we now know is false, Bigman et al., 2018;Jager & Dekkers, 1975;Palzenberger & Pohla, 1992;Wegner, 2011). ...
... Second, we reran all models without those species traditionally used in aquaculture because the growth of 'aquacultured' species is known to differ from that of wild fishes due to food ad libitum, reduced predation and possibly increased aeration of aquaculture ponds (Pauly, 2010). Third, we reran all models without air-breathing fishes because fishes that breathe air either by possessing an air-breathing organ or passive oxygen diffusion through the skin often have a lower gill surface area for a given body size compared to their non-air-breathing counterparts (Graham, 1997;Wegner, 2011). Finally, we also ensured that our regression coefficients were not sensitive to a threshold of eight species for estimating an allometry -for this, we limited our raw data set to those species with gill surface area measurements that ranged over an order of magnitude of body mass (n = 34 species). ...
The Gill Oxygen Limitation Theory (GOLT) posits that a mismatch in oxygen supply and demand stemming from geometric constraints on gill surface area limits metabolic rate and energy available for biological processes. This theory has been suggested to explain numerous phenomena observed with warming yet is based upon a relationship among maximum size, growth, and gill surface area established over 40 years ago. However, the metric used in this relationship to characterize gill surface area, gill area index, fails to capture the known variability in the scaling of gill surface area and is biased by the sizes at which gills were measured. Here, we revisit a central prediction of the GOLT, asking four key questions that examine limitations in the original relationship. We find that gill area index does indeed explain variation in growth performance across 132 species of fish and this relationship is strikingly similar to the original relationship across 42 species. Yet, we argue that gill area index is not an adequate measure of gill surface area because (1) it has a non‐linear relationship with size and, thus, changes ontogenetically as an individual grows over time and (2) because it is based on mean estimates of both gill surface area and body mass. Indeed, we show that the value of gill area index for a given species is variable depending on how it is calculated. We therefore suggest a pathway forward for assessing whether gill surface area is an important factor in explaining variation in growth performance.
... For example, a fast-swimming oceanic fish, such as a tuna (family Scombridae), can have a gill surface area that is an order of magnitude larger and a thickness of the gill epithelium (the water-blood barrier) that can be an order of magnitude thinner than those of a "sluggish" marine fish. The simplicity of comparing such fish ecomorphotypes to demonstrate their diversity and the various factors shaping gill functional morphology has been repeated in subsequent reviews of gill dimensions (e.g., Palzenberger and Pohla, 1992;Wegner, 2011). In my review chapter in the Encyclopedia of Fish Physiology (Wegner, 2011), I purposely included these same groups from Hughes (1984) with additional categories including 5. Freshwater fishes and 6. ...
... The simplicity of comparing such fish ecomorphotypes to demonstrate their diversity and the various factors shaping gill functional morphology has been repeated in subsequent reviews of gill dimensions (e.g., Palzenberger and Pohla, 1992;Wegner, 2011). In my review chapter in the Encyclopedia of Fish Physiology (Wegner, 2011), I purposely included these same groups from Hughes (1984) with additional categories including 5. Freshwater fishes and 6. Hypoxia dwellers. ...
... The basic components of gills include the gill arches, gill filaments, gill rakers and the lamellae. Most of the fishes have four pairs of gills positioned bilaterally on each side of oral cavity (Wegner, 2011). The gills have a role in variety of key functions in fish, including breathing, ionic regulation, osmosis regulation, acid base balance, ammonia excretion, hormone production, modulation of circulating metabolites and immune defense (Rombough, 2007) . ...
... Abbreviations: ABA, afferent branchial artery; AFA, afferent filament artery; EBA, efferent branchial artery; EFA, efferent filament artery; IMC, inner marginal channel; RBC, red blood cell. Drawings modified from Palzenberger and Pohla (1992), Wegner (2011Wegner ( , 2016. ...
... where m is the dynamic viscosity of the water, l is the interlamellar channel length, d is the diameter or width of the interlamellar channel, w is the width or thickness of a lamella, and h is lamellar height (dimensions shown in Fig. 2) (Wegner, 2011). To obtain a large gill surface area, fish can increase the length (l), height (h), or frequency (decreasing d) of their lamellae, or increase the length of the gill filaments (L fil ). ...
... As fishes inhabit a range of aquatic habitats and ecological niches, both gill area and the water-blood barrier thickness range more than an order of magnitude depending on the specific demands associated with a species' metabolic requirements and physiochemical surroundings. As a result, distantly related taxonomic groups show remarkable evolutionary convergence in gill morphology, and previous reviews of gill morphology and function have categorized fishes into different morphological ecotypes based on their gill dimensions (Gray, 1954;Hughes, 1984;Palzenberger and Pohla, 1992;Wegner, 2011). The reader is referred to Chapter 166: Gill Respiratory Dimensions (Wegner, 2011) in the first edition of this Encyclopedia for more detailed descriptions of fishes as grouped by gill diffusion capacity. ...
The fish gill has been optimized over millions of years of evolution to provide vital functions in respiratory gas exchange,
osmoregulation, acid-base balance, and nitrogenous waste excretion. Despite a fairly consistent basic morphology, clear
differences in gill size, thickness, and function reflect the varying physiological requirements of fishes living in diverse and
sometimes challenging aquatic habitats. In many cases, the fish gill also shows the ability to adjust to changing environmental
conditions in a matter of days to weeks. This article highlights trends in the plasticity of gill morphology and function
on both long-term (evolutionary) and short-term (acclimation) time scales.
... In fish culture, ectoparasite infestations are prevalent and can impair gill function, leading to respiratory and osmoregulatory failure (Ojha & Hughes 2001), and this is unsurprising considering gills are among some of the most complex and sensitive structures (Evans et al. 2005, Wegner 2011, Gilmour & Perry 2018. In environmental conditions that impair physiological function, the gill epithelia can become eroded and inflamed (Mallatt 1985). ...
... The space around epithelial layers is perfused with blood. The epithelium provides only a thin barrier between the fish's blood and the surrounding water (Evans et al. 2005, Wegner 2011). The large lamellar surface area may increase the susceptibility of gills to parasitic infestations (Ojha & Hughes 2001, Nilsson et al. 2012, Abdel-Latif et al. 2020. ...
High mortality is among the most serious problems and challenges in the ornamental fish trade. Examination of the discus Symphysodon aequifasciatus from ornamental fish hatchery revealed infestation with the monogenean Sciadicleithrum variabilum . Gill infestation with this monogenean induced serious damage to the gill lamellae, including clavate lamellae, vascular congestion in the peripheral blood vessels, lamellar blood sinus dilation, and other structural anomalies. Light and transmission electron microscopy showed that in all infested hosts the interlamellar cell mass (ILCM) completely filled the interlamellar space. The monogenean-associated damage combined with the ILCM led to severe impairment of respiratory efficiency of the gill. Anti-parasitic treatment was applied during breeding (hatchery), which was followed by almost complete regression of the ILCM seen in the fish. A single point of ILCM hyperplasia was observed in only one specimen at the site of parasite attachment to the gill filament. The ILCM covering the gill lamellae protected the discus against infestation with this monogenean, but considerable reduction in the gaseous exchange surface and serious damage to the gill lamellae contributed to the increased mortality of the fish in the hatchery, which reached 90%.
... Równanie 2) Przekształcone równanie Ficka (za Wegner, 2011 Dodatkowo w nabłonku skrzeli zachodzi eliminacja szkodliwych związków azotowych powstałych w procesach metabolicznych (Evans i in., 2005;Kilarski, 2012b;Peterson, 2015;Roberts i Ellis, 2012;Speare i Ferguson, 2006;Wegner, 2011). Ruch ten odbywa się przez okienka błony podstawnej, które występują licznie w MALT (Bayne i Gerwick, 2001;Bjørgen i Koppang, 2021;Dalmo i in., 1997;Ellis, 2001;Esteban, 2012;Koppang i in., 2015;Randelli i in., 2008;Rességuier i in., 2020;Salinas, 2015;Tort i in., 2003;Zhang i in., 2010). ...
... Równanie 2) Przekształcone równanie Ficka (za Wegner, 2011 Dodatkowo w nabłonku skrzeli zachodzi eliminacja szkodliwych związków azotowych powstałych w procesach metabolicznych (Evans i in., 2005;Kilarski, 2012b;Peterson, 2015;Roberts i Ellis, 2012;Speare i Ferguson, 2006;Wegner, 2011). Ruch ten odbywa się przez okienka błony podstawnej, które występują licznie w MALT (Bayne i Gerwick, 2001;Bjørgen i Koppang, 2021;Dalmo i in., 1997;Ellis, 2001;Esteban, 2012;Koppang i in., 2015;Randelli i in., 2008;Rességuier i in., 2020;Salinas, 2015;Tort i in., 2003;Zhang i in., 2010). ...
Rainbow trout (Oncorhynchus mykiss Walbaum, 1792) is the leading species of Polish aquaculture, as well as one of the most important species of farmed fish in Europe and globally. The world population is estimated to reach 10 billion by 2050. To meet the expected nutritional requirements of a growing population, aquatic animal production must double by 2050, and any increase will have to come from aquaculture as environmental opportunities are compromised. Diseases are the greatest threat to the development of this food production sector and increasing climate changes may increase the risk of their emergence and spread. To minimize the risk of diseases and the need for fish treatment, it is important to take biosecurity and preventive measures, which include, inter alia, antiseptic baths. There is a scarcity of scientific reports on the effects of doses of antiseptics on pathomorphology of trout, which are used in veterinary ichthyopathological practice. There is also a lack of standardized comparative studies that would allow a proper risk-benefit assessment in terms of health if a decision must be made to use antiseptic substances in trout farming.
The work aims to determine and compare the effect of single, double, and triple prophylactic bath treatments with the use of formaldehyde (dose of 0,25 kg m-3), sodium chloride (dose of 20 kg m-3) and copper (II) sulphate (dose of 0,003 kg m-3) on the pathomorphology of the skin and gills of clinically healthy rainbow trout. Fry of rainbow trout in number 360, age 0+ with an average weight of 88,87±32,53 g was used in the experiment. Fragments of skin and gills were sampled from each animal and fixed in Davidson's fixative. Tissue sections were subjected to standard histopathological processing and then stained according to two methods: haematoxylin-eosin and Alcian blue/periodic acid–Schiff reagent. 1 440 slides were evaluated. The work uses semi-quantitative methods, such as the assessment of condition-related indicators and histopathological evaluation with the use of organ reaction indices.
The obtained results showed that a single exposure to formalin at a dose of 0,25 kg m-3, with safety measures in the form of increased aeration in tanks, had no toxic effect on the skin and had a very weak effect on the morphological image of trout gills. Formalin toxicity was found to increase with the use of subsequent doses. It has been shown that a single exposure to sodium chloride at a dose of 20 kg m-3 has a stronger effect on the pathomorphology of the examined trout organs than a single exposure to formalin, and the difference between effects of these substances on the pathomorphology of trout skin and gills decreases with the exposure to the second and third dose. The study confirmed the toxic effect of sodium chloride on the analysed organs, manifested in the tested parameters. Regardless of the number of doses, the application of the bath treatment with copper (II) sulphate in the dose of 0,003 kg m-3 resulted in the most intense pathomorphological changes.
