ABSTRACT

The comparative acute toxicity of the aqueous extract of Aloe barbadensis leaves and roots against fingerlings of the African Catfish (clarias gariepinus) was conducted under static bioassay in the laboratory for 96h to examine and compare the toxic effects of the plant leaves and roots on the fish, Clarias gariepinus.  Range finding bioassays were conducted to get the range of concentration for the definitive bioassays. The range of concentrations of test media for the leaves was 0-650mgL-1 while that of the roots was 0-980mgL-1. The median lethal concentrations (LC50) were determined using pro bit analysis. Ten active experimental organisms of about the same size were randomly placed with scoop net in each of the test medium, each concentration having replicate including untreated media. The 96hLC50 of the leaves against exposed fingerlings was 380.6mg/L with lower and upper confidence limits of 324.3 and 426.1mg/L respectively while that of the roots was 554.7mg/L with lower and upper confidence limits of 609.5 and 606.7mg/L respectively.  Paired t-test showed that there was no significant difference (P>0.05) between the test A. barbadensis leaves and roots against the test species.  The water quality parameters showed that the leaves caused increased temperature, conductivity, dissolve oxygen, pH, alkalinity, hardness and ammonia while the roots caused an increase in temperature, conductivity, alkalinity, hardness and ammonia and there was a decrease in pH while dissolved oxygen remained the same. It can be concluded from this study that both the leaves and the roots of the plant material are toxic to fish with the leaves being more potent.

CHAPTER ONE

1.1     Introduction

The use of plants for healing purpose is getting increasingly popular as they are believed as being beneficial and free of side effect (Leonardo et al., 2000).  The use of plant materials as spices, condiments and for medicinal purposes has therefore become more popular and as such more wild plants are being exploited for medicinal purpose.  There is therefore no doubt that orthodox medicine itself appears to be strongly anchored on traditional medicine (Nweze, 2005).  Plants are used for different purposes because some plants contain compounds of various class that have insectidal, piscicidal and molluscicidal properties (Cagauan, 1992).  However, the occurrences of these fish poison plants are varied based on location. Different parts of plants which contain toxic substances used in poisoning fish include the roots, seeds, fruits, barks or leaves (Gabriel and Okey, 2009).  According to Gabriel and Okey (2009), ichthyotoxic plants used for baiting and stupefying of fish are often crushed and cast into stagnant, slow moving water or spread on  mud flats to poison fish.  Ichthyotoxic plants have been used as fish poisons or narcosing chemicals by the artisanal fishermen for decades in the harvesting of fish in slow flowing waters (Oribhabor et al., 2014).

          According to Neuwinger (2004) and Fafioye et al. (2004), the use of fish poison plants and other plant products is one of the methods in traditional methods of fish capture.  Plant extracts used as piscicides in capture fisheries and aquaculture are considered advantageous when compared to the back drop of using persistent and synthetic chemicals (Gabriel and Okey, 2009).  Phytochemical evaluation indicates that such piscicidal or ichthyotoxic plants contain different active ingredients known as alkaloids such as nicotine, pyrethrum, ryania, rotenone, resin, akuammine, tannins, saponins and diosgenin (Wang and Huffman, 1991). Ichthyotoxins present in these fish poison plants will stun fish when it passes through the gills or in some cases when ingested, it makes the fish to float on the water surface for easy capture (Kritzon, 2003).

          Aloe vera (Aloe barbadensis), a member of the family liliaceae, is a naturally occurring perennial succulent plant that is cactus-like in its characteristics, originating from Northern Africa (Akinyale and Odiyi, 2007).  Aloe’s thick, tapered, spiny leaves grow from a short stalk near ground level.  Aloe’s relationship to the lily family is evident from the tubular yellow flowers produced annually in the spring that resemble those of the Easter lily (Amit and Shweta, 2016).

          Important pharmaceutical properties that have recently been discovered for the aloe vera gel and whole leaf extracts includes the ability to improve bioavailability of co-administered vitamins on human subjects (Chandan et al., 2007).  The biological activities include promotion of wound healing, antifungal activity, hypoglycemic or anti-diabetic effects, anti-inflammatory, anti cancer, immuno-modulatory and gastro-protective properties. Furthermore, an increase in bile flow and bile solids as a result of treatment with the extract suggests stimulation of the secretary activity of the liver cells.  The hepatoprotective action is also attributed to preserving the metabolizing enzyme of the liver through an antioxidant activity (Ambrose et al., 1994; Zodape, 2010).  In Nigeria, there is a very strong cultural belief in herbal medicare, most often due to the latter’s economic advantage and easier reach compared to the high cost of orthodox medicine.  This is more compounded by low literacy levels and often epileptic and grossly inefficient orthodox healthcare delivery system.  Since the sudden introduction and widely acclaimed mega-therapeutic potentials of aloe vera and its products in the mid 1990s, and the highly expensive “processed” Aloe vera products, it is a common site to see homestead aloe vera “plantations” at every corner in most towns and villages.  This has led to unrecommended and uncontrolled consumption of raw Aloe vera leaves by highly and mighty in the society.

          Reports have been documented in the therapeutic potentials of Aloe vera (Schmidt and Greenspoon, 1993), its toxicity, especially when used parenterally (Brusick and Menge, 1997;  Balter, 1992).  Report have shown that consumption of Aqueous extract of Raw Aloe vera leaves in the histopathological and biochemical studies in Rat and Tilapia tends to be lethal to fish at as low as 50ppm in water causing 100% mortality within 96 hours (Taiwo et al., 2005). Methanolic extract of Aloe vera’s toxicity have also been tested on rats (Saritha et al., 2010).  A study on analgesic efficacy and adverse effects of aloe vera in wistar rats have also been carried out (Ghosh et al., 2011).  Aloe vera has also been used to study its dietary effects on growth performance, skin and gastro-intestine morphology in rainbow Trout (Oncorhynchus mykiss).

 The African catfish (Clarias gariepinus) belonging to the family clariidae is the most cultivated species in Nigeria.  This is attributed to its ability to tolerate a varying  range of environmental conditions, high stocking densities  under culture condition, fast growth rate, disease resistance, acceptability of artificial feed, high fecundity, good taste and meat quality, ease of artificial breeding, high market value etc (Eyo et al., 2014). African catfish (Clarias gariepinus) is one of the highly priced food fish in Nigeria and most parts of the world.  An Omnivorous scavenger that eats everything it finds, the African catfish is particularly amenable to the farming practices of smallholders, who comprise the majority of farmers in developing countries (Musa et al., 2012, Ajala and Owoyemi, 2015).  African catfish is rated the third most cultured fish in the world (Offem et al., 2010).

          Biologically, the African catfish (Clarias gariepinus), is undoubtedly an ideal aquaculture species.  It is widely distributed, not only in African countries but also in the Netherlands; it thrives in diverse environments, temperate to tropical (Hecht et al., 1996).  It is hardy and adaptable principally as a consequence of its air breathing ability, feeds in a wide array of natural prey under diverse conditions, is able to withstand adverse environmental conditions, is highly resistant to diseases, and is highly fecund and easily spawned under captive conditions.  It has a wide tolerance of relatively poor water quality and possibly the most exciting feature of the species is its potential for highly intensive culture without prerequisite pond aeration or high water exchange rates and its excellent meat quality (Hecht et al., 1996)

          Although this plant, Aloe vera (Aloe barbadensis) have been used in several toxicological studies, little or no information have been documented on its toxic effects in the African catfish (Clarias gariepinus).  Also, most of the documented works have been carried out using only the leaves of the plant but in this research, I will be comparing the toxic effect of both the plant’s leaves and roots against the African catfish (Clarias gariepinus).

1.2     Objectives of the study

          The objectives of this research are to:

a)       Investigate the toxicity of Aloe vera (Aloe barbadensis) leaves and roots in Clarias gariepinus fingerlings.

b)      Determine the phytochemical composition of the ichthyotoxic plants, Aloe vera (Aloe barbadensis).

c)       Determine the acute toxicity (LC50) of the aqueous extract of Aloe barbadensis on fingerlings of Clarias gariepinus under 96hours static bioassay.

d)      Compare the toxic effects of Aloe vera (Aloe barbadensis) leaves and roots against Clarias gariepinus.

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