**3. Chemical contaminants in aquatic systems**

Toxic compounds or natural anthropogenic are called xenobiotics. With the onset of the epidemiological investigations was to confirm the hypothesis of many xenobiotics to be dangerous to living things, as well as their respective offspring, exerting toxic effects in the short, medium or long term (Reys, 2001). These substances are persistent in the envi‐ ronment eventually absorbed and accumulated by living organisms, toxic effects on vari‐ ous organs and systems. Thus, it was noted that the use of xenobiotics without evaluation of risks to the ecosystem, constituted a potential threat to the health of peo‐ ple, animals and plants (Sanches, 2006).

The introduction of toxic substances in the aquatic environment causes local and immediate effects, but can also lead to contamination of watersheds and commitment of underground reservoirs by infiltration through the soil. Numerous compounds have been detected in sur‐ face water, groundwater and water supply relating to agricultural activities and human cas‐ es of environmental contamination (Sanches, 2006).

#### **3.1. Insecticides**

sure of aquatic organisms to insecticides at environmentally relevant concentrations

Pesticides in the environment may be used as a model for the study of ecotoxicology, be‐ cause they contaminate air, land and water, causing adverse effects that affect from bacteria to humans. It is well proven that these chemicals are toxic to aquatic arthropods, bees and fish (Santos et al., 2007). The effects of the use of pesticides are recognized worldwide and aggravated by misuse since part of this material is accumulated in plants and soil and much

As a result of a great variety of human activities, the aquatic environment is becoming in‐ creasingly threatened by an alarming number of foreign chemicals or xenobiotics. Fish pop‐ ulations living in highly polluted areas often have high incidences of gross pathological lesions (Malins et al., 1988), associated with elevated levels of toxic contaminants in the sedi‐ ments. However, pesticides applied to the land may be washed into surface waters and may

Contamination of water with large amounts of pesticides leads to fish mortality or star‐ vation by destruction of food organism, many toxicants have been shown to affect growth rate, reproduction and behavior, with evidence of tissue damage (Van Der Oost

The poisoning of fish by pesticides can be acute or chronic and in general acute poisoning causes mass mortality. However, pollution is an often chronic process, apparently without any visible damage but sometimes producing several sublethal effects (Rodrigues, 2003).

The aim of this chapter was present a review based on some aspects of silver catfish's

Silfvergrip (1996) conducted extensive taxonomic revision of the genus based on characters of internal morphology, and concluded that the genre *Rhamdia* consists of only 11 species among 100 previously described. According to the same author, quelen taxonomic division belongs to the following: Class: Osteichthues, Series: Teleostei, Order: Siluriformes, Family:

*Rhamdia quelen*, popularly known, as silver catfish is a species of fish found from southern Mexico to Argentina that displays the absence of teeth and scales with variable-length cylin‐ drical wattles. This is an omnivorous species with an eating preference for fish, crustaceans,

The silver catfish (*Rhamdia quelen,* Quoy & Gaimard) is an endemic South American fish spe‐ cies that with stands cold winters and presents fast growth rate in summer. These character‐ istics make catfish a suitable species for fish production in southern South America or any region with a temperate or subtropical climate. In aquaculture systems, at a density of two

of it is transported to the rivers by rain (Tsuda et al., 1995; Wilson; Tisdell, 2001).

kill or at least adversely influence the life of aquatic organisms.

(Das; Mukherjee, 2003).

198 New Advances and Contributions to Fish Biology

et al., 2003; Srivastav et al., 2002).

Pimelodidae. Genre: Rhamdia, Species: quelen.

insects, plants and organic debris (Silfvergrip, 1996).

toxicology.

**2. The fish**

The growing use of synthetic insecticides is intensifying global pollution risks. Insecti‐ cides are toxic and were designed to repel or kill unwanted organisms and when used for their different purposes they may be brought to water bodies killing or influencing the lives of aquatic organisms (El Sayed et al., 2007). The effects of the use of insecti‐ cides are recognized worldwide and compounded by their improper use (Tsuda et al., 1995; Wilson; Tisdell, 2001).

Organophosphates comprise a group of chemical compounds extensively used in farming as insecticides, which cause accidental poisoning in animals and men. The toxicity of these compounds is due especially to the respiratory and cardiac impairment in consequence of autonomic nervous system disorders.

The primary effect of organophosphates (Ops) on vertebrate and invertebrate organisms is the inhibition of the enzyme Acetylcholinesterase (AChE), which is responsible for terminat‐ ing the transmission of the nerve impulse. OPs block the hydrolysis of the neurotransmitter acetylcholine (ACh) at the central and peripheral neuronal synapses, leading to excessive ac‐ cumulation of ACh and activation of ACh receptors (Peña-Llopis et al., 2003). The oversti‐ mulation of cholinergic neurones initiates a process of hyperexcitation and convulsive activity that progresses rapidly to *status epilecticus*, leading to profound structural brain damage, respiratory distress, coma, and ultimately the death of the organism if the muscar‐ inic ACh receptor antagonist atropine is not rapidly administered (Shih; Mcdonough, 1997).

Fipronil is a non-systemic, chiral phenylpyrazole insecticide registered for use to control ants, beetles, cockroaches, fleas, mole crickets, ticks, termites, thrips, and other insects in a variety of agricultural and residential uses. Its mechanism of action involves non-competi‐ tive binding to the GABA receptor, effectively blocking the chloride channel and resulting in

Evaluation of Toxicity in Silver Catfish http://dx.doi.org/10.5772/53899 201

Their toxicity to fish varies with species and it is highly toxic to *Lepomis macrochirus* (LC50 = 85 g/L), the *Oncorhynchus mykiss* (LC50 = 248 g/L), the *O. niloticus* (LC50 = 42 mg/L), *Poecilia reticulata* (LC 50 less than 100 g/L) and *Cyprinus carpio* (LC50 = 430 g/L). Low concentrations of fipronil are lethal to most species of fish that were tested, and is especially toxic to young fish. Studies indicate that the dose 15 mg/L reduced the growth of trout. In addition, this

The occurrence of pharmaceuticals for human and veterinary use has been detected in sur‐ face waters, sediments and drain in worldwide. Various substances such as anti-inflamma‐ tories, analgesics, antibiotics, hormones and antidepressants represent them. Although they have been subjected to pharmacokinetic studies, little information exists about the environ‐ mental fate and toxic effects in several organisms of aquatic fauna and flora, certainly affect‐

Chemical toxicity distribution approaches have been employed for identifying Thresholds of Toxicological Concern for many industrial chemicals (Kroes et al., 2005), comparing the sensitivities of in vitro and fish models for estrogenicity (Dobbins et al., 2008), and predict‐ ing aquatic concentrations of ecotoxicological concern for chemical with common MOAs in

The biological response of an organism to xenobiotics following absorption and distribution starts with toxicant induced changes at the cellular and biochemical levels, leading to changes in the structure and function of the cells, tissues, physiology and behavior of the organism. These changes can perhaps ultimately affect the integrity of the population and ecosystem. For the biomonitoring and management of the aquatic ecosystems, these biologi‐ cal responses (biomarkers) have been proposed to complement and enhance the reliability

There are very few pollutants that have been confirmed to cause adverse effects. In most cases, casual relationships have not been established to a large group of persistent pollu‐ tants, due the complex chemical contamination of environmental compartments, which dif‐ ficulty to attribute harmful effects to any particular pollutant or category of pollutants.

Several definitions have been given for the term 'biomarker', which is generally used in a broad sense to include almost any measurement reflecting an interaction between a biologi‐

paralysis (USEPA, 2011).

**3.2. Drugs**

compound is also bioaccumulated fish.

ed (Stumpf et al., 1999; Fent et al. 2006).

plant models and invertebrates and fish (Dobbins et al., 2008).

**4. Assessment of toxicity in fish by biomarkers**

of the chemical analysis data (Parvéz; Raisuddin, 2005).

Melo (2004) showed that *Rhamdia quelen* (silver catfish) juveniles exposed for 96 hours to a sublethal dose (0.01 mL/L) of Folidol® 600, was target for the toxicant action and some alter‐ ations became evident after 4 hours of exposure. The alterations observed in the liver were reduction in the density of melanomacrophages, focuses of necrosis, enhancement in the density of hepatocytes, loss of the cellular contour of the hepatocytes, cytoplasmic granula‐ tion, reduction of the cytoplasmic vacuolization, mithocondrial disruption, disorganization of the rough endoplasmic reticulum, nuclear heterochromatization and decharacterization of the endothelium. These alterations could diminish the liver metabolism, and as a conse‐ quence, they could cause damages to the health of the *R. quelen* juveniles.

Deltamethrin (DM) and other pyrethroids have proven to be toxic to aquatic organisms, mainly to fish. Due to its lipophilic characteristics it can be highly absorbed by the fish gills, which partially explains the high sensitivity of these animals to DM exposure in concentra‐ tions up to a thousand times lower than in mammals (Rodrigues, 2003).

Galeb et al. (2010) and Montanha (2010) studied the behavior of silver catfish exposed to sublethal concentrations of DM and CM, respectively, and they have presented loss of balance, swimming alteration, dyspnea (they kept their mouths and opercula open). *Post-mortem* signs observed in the animals exposed to DM and CM were mainly darken‐ ing of the surface of the body, tail and wattles erosion and hemorrhagic spots on the body surface.

The main behavioral changes observed are represented by respiratory and neurological manifestations. Such results corroborate with Polat et al. (2002) and Ylmaz et al. (2004), who have tested Cypermethrin in guppies (*Poecilia reticulata*); Borges (2007), who have tested CM in silver catfish (*Rhamdia quelen*). These changes can be attributed to the neurotoxic effect of DM/CM by blocking sodium channels and inhibiting the GABA receptors in the nervous fil‐ aments which results in an excessive stimulation of the central nervous system that some‐ times can lead to brain hypoxia (El- Sayed et al., 2007).

Galeb et al. (2010) studied the haematological response of silver catfish exposed by DM, it was a significant increase in the total leukocyte counts. Similar results were reported by El-Sayed et al. (2007) in Nile tilapia (*Oreochromis niloticus*) and Pimpão et al. (2007) in catfish (*Ancistrus multispinis*). Montanha (2010) showed similar results in silver catfish ex‐ posed to CM. The leukocytosis showed that these pesticides can generate inflammatory or stress responses.

It was observed decrease of serum levels of ALT (alanine aminotransferase), AST (aspartate aminotransferase) and FA (alkaline phosphatase) were observed in silver catfish exposed to DM (Galeb, 2010) and CM (Montanha, 2010).

Fipronil is a non-systemic, chiral phenylpyrazole insecticide registered for use to control ants, beetles, cockroaches, fleas, mole crickets, ticks, termites, thrips, and other insects in a variety of agricultural and residential uses. Its mechanism of action involves non-competi‐ tive binding to the GABA receptor, effectively blocking the chloride channel and resulting in paralysis (USEPA, 2011).

Their toxicity to fish varies with species and it is highly toxic to *Lepomis macrochirus* (LC50 = 85 g/L), the *Oncorhynchus mykiss* (LC50 = 248 g/L), the *O. niloticus* (LC50 = 42 mg/L), *Poecilia reticulata* (LC 50 less than 100 g/L) and *Cyprinus carpio* (LC50 = 430 g/L). Low concentrations of fipronil are lethal to most species of fish that were tested, and is especially toxic to young fish. Studies indicate that the dose 15 mg/L reduced the growth of trout. In addition, this compound is also bioaccumulated fish.

#### **3.2. Drugs**

acetylcholine (ACh) at the central and peripheral neuronal synapses, leading to excessive ac‐ cumulation of ACh and activation of ACh receptors (Peña-Llopis et al., 2003). The oversti‐ mulation of cholinergic neurones initiates a process of hyperexcitation and convulsive activity that progresses rapidly to *status epilecticus*, leading to profound structural brain damage, respiratory distress, coma, and ultimately the death of the organism if the muscar‐ inic ACh receptor antagonist atropine is not rapidly administered (Shih; Mcdonough, 1997). Melo (2004) showed that *Rhamdia quelen* (silver catfish) juveniles exposed for 96 hours to a sublethal dose (0.01 mL/L) of Folidol® 600, was target for the toxicant action and some alter‐ ations became evident after 4 hours of exposure. The alterations observed in the liver were reduction in the density of melanomacrophages, focuses of necrosis, enhancement in the density of hepatocytes, loss of the cellular contour of the hepatocytes, cytoplasmic granula‐ tion, reduction of the cytoplasmic vacuolization, mithocondrial disruption, disorganization of the rough endoplasmic reticulum, nuclear heterochromatization and decharacterization of the endothelium. These alterations could diminish the liver metabolism, and as a conse‐

Deltamethrin (DM) and other pyrethroids have proven to be toxic to aquatic organisms, mainly to fish. Due to its lipophilic characteristics it can be highly absorbed by the fish gills, which partially explains the high sensitivity of these animals to DM exposure in concentra‐

Galeb et al. (2010) and Montanha (2010) studied the behavior of silver catfish exposed to sublethal concentrations of DM and CM, respectively, and they have presented loss of balance, swimming alteration, dyspnea (they kept their mouths and opercula open). *Post-mortem* signs observed in the animals exposed to DM and CM were mainly darken‐ ing of the surface of the body, tail and wattles erosion and hemorrhagic spots on the

The main behavioral changes observed are represented by respiratory and neurological manifestations. Such results corroborate with Polat et al. (2002) and Ylmaz et al. (2004), who have tested Cypermethrin in guppies (*Poecilia reticulata*); Borges (2007), who have tested CM in silver catfish (*Rhamdia quelen*). These changes can be attributed to the neurotoxic effect of DM/CM by blocking sodium channels and inhibiting the GABA receptors in the nervous fil‐ aments which results in an excessive stimulation of the central nervous system that some‐

Galeb et al. (2010) studied the haematological response of silver catfish exposed by DM, it was a significant increase in the total leukocyte counts. Similar results were reported by El-Sayed et al. (2007) in Nile tilapia (*Oreochromis niloticus*) and Pimpão et al. (2007) in catfish (*Ancistrus multispinis*). Montanha (2010) showed similar results in silver catfish ex‐ posed to CM. The leukocytosis showed that these pesticides can generate inflammatory

It was observed decrease of serum levels of ALT (alanine aminotransferase), AST (aspartate aminotransferase) and FA (alkaline phosphatase) were observed in silver catfish exposed to

quence, they could cause damages to the health of the *R. quelen* juveniles.

tions up to a thousand times lower than in mammals (Rodrigues, 2003).

times can lead to brain hypoxia (El- Sayed et al., 2007).

DM (Galeb, 2010) and CM (Montanha, 2010).

body surface.

200 New Advances and Contributions to Fish Biology

or stress responses.

The occurrence of pharmaceuticals for human and veterinary use has been detected in sur‐ face waters, sediments and drain in worldwide. Various substances such as anti-inflamma‐ tories, analgesics, antibiotics, hormones and antidepressants represent them. Although they have been subjected to pharmacokinetic studies, little information exists about the environ‐ mental fate and toxic effects in several organisms of aquatic fauna and flora, certainly affect‐ ed (Stumpf et al., 1999; Fent et al. 2006).

Chemical toxicity distribution approaches have been employed for identifying Thresholds of Toxicological Concern for many industrial chemicals (Kroes et al., 2005), comparing the sensitivities of in vitro and fish models for estrogenicity (Dobbins et al., 2008), and predict‐ ing aquatic concentrations of ecotoxicological concern for chemical with common MOAs in plant models and invertebrates and fish (Dobbins et al., 2008).
