Effects of water hyacinth ( Eichhornia crassipes ) on the physicochemical properties of fishpond water and growth of African catfish

Water hyacinth (Eichhornia crassipes) is an aquatic plant that has the capacity to absorb nutrients, making it a potential alternative for the management of fishpond water. The effect of this plant on the physicochemical properties of fish pond water and on the growth of African catfish was investigated in this study. Four plastic ponds 2.0×2.0×1.2 m deep were used for the study. Fifteen percent of the surface area of two of the ponds was covered with water hyacinth while the other two ponds, which served as the control, were left uncovered. African catfish juveniles, with an average weight of 0.3 kg, sourced from a commercial fish farm, were used to stock each of the ponds at a density of 30 m -2 . The fish were fed with commercial feed pellets at an average rate of 0.33 g/fish/day. Water samples were drawn from the ponds weekly and analyzed for relevant physicochemical parameters. Based on the observed oxygen content of the ponds, the water in the control ponds were changed every week while those of the ponds with water hyacinth were changed bi-weekly. Fish samples were randomly selected weekly from each pond and weighed to determine the fish growth. The study lasted for four weeks. Results showed that the mean concentrations of total dissolved solids (TDS), total hardness, Mg hardness, chloride, nitrate, nitrite, sulphate, conductivity, turbidity and dissolved oxygen (DO) were higher, but not significantly (P≤0.05), under water hyacinth cover. Other parameters such as ammonia and biochemical oxygen demand (BOD) were higher in the control pond. All parameters were fairly within the acceptable limits. There was also no significant difference (P≤0.05) between the final average weight of the fish in the ponds with water hyacinth (0.85 kg) and the control ponds (0.69 kg). Apart from reduction in water use, it would appear that the use of water hyacinth does not confer any significant advantage in fish ponds.

a major resource and constitutes a significant percentage of the production cost in fish ponds (Isyagi et al., 2009).The high feeding levels necessary to sustain semiintensive and intensive fish culture systems contribute large amounts of nutrients in the pond water.This, if not controlled, leads to excessive algal growth and depletion of the oxygen content of the water which in turn affects the growth of the fish.Unless there is a way of rapidly removing the nutrient from the water, the pond water must be changed frequently for effective and efficient fish production.Frequent change of fish pond water naturally leads to increase in the production cost, especially where water is supplied by pumping (Isyagi et al., 2009).Water hyacinth is known to absorb nutrients from water bodies (Aoi and Hayashi, 1996;Snow and Ghaly, 2008;Adeniran, 2011;Ochekwu and Madagwa, 2013;Ugya and Imam, 2015) and so appears to be a good solution to the management of fish pond water.
Water hyacinth, Eichhornia crassipes (Mart.) is a floating vascular plant which is believed to have originated from South America.It is one of the world's most prevalent invasive aquatic plants (Villamagna, 2009;Gupta et al., 2012).Villamagna (2009) noted that water hyacinth is prevalent in tropical and subtropical water bodies where nutrient levels are often high due to agricultural runoff, deforestation, and insufficient wastewater treatment.Water hyacinth is comprised of approximately 90% water, making it very heavy to transport (Gopal, 1987;Gupta et al., 2012).It commonly forms dense, interlocking mats due to its rapid reproductive rate and complex root structure, reproducing both sexually and asexually (Mitchell, 1985;Gupta et al., 2012).Its capacity to absorb nutrients makes it a potential biological alternative to secondary and tertiary treatment for sewage and other contaminated water (Cossu et al., 2001;Adeniran, 2011;Ochekwu and Madagwa, 2013;Ugya and Imam, 2015).Furthermore, it is known to increase invertebrate abundance and diversity by providing habitat within its complex root system (Brendonck et al., 2003;Toft et al., 2003).The dense and intricately connected root system also provides refuge and nursery habitat for small and juvenile fish as well as zooplankton (Brendonck et al., 2003).
Information on the effect of water hyacinth on ponds, particularly on ponds stocked with African catfish, is scarce.There are very few studies that report the ecological effect of water hyacinth on aquatic bodies which make it difficult to understand fully how it may alter an ecosystem (Villamagna, 2009).Hence, it is necessary to investigate the effects of water hyacinth on a pond stocked with African catfish to determine the direct and indirect effects of this aquatic plant on fish ponds.Indeed, the lead author of this paper once visited a commercial fish farm in Abakaliki, Eastern Nigeria, in which one of the ponds had water hyacinth planted on the surface.The farmer believed that it results in higher fish production.However, there was no empirical data to support his belief.This study was therefore carried out to investigate the effect of water hyacinth on the water quality of fish ponds, stocked with African catfish as well as the fish growth.African catfish (Clarias gariepinus) was chosen for this study because it is the most predominantly reared fish in Nigeria.

The experimental ponds
The study is a two factor (ponds with and without water hyacinth) experiment with two replications.Four experimental artificial ponds consisting of plastic tanks with dimensions of 2.0 × 2.0 × 1.2 m deep were used for this study.The ponds were located at Mosco Fish Farm in Enugu South Local Government Area, Enugu State, Nigeria.The ponds were placed side by side so as to keep them exposed to the same environmental conditions.The ponds were filled with water sourced from a near-by stream.They were stocked with post juvenile African catfish with an initial average weight of 0.3 kg, which was obtained from Mosco Fish Farm.The choice of the fish species is based on the fact that African catfish is the predominantly reared fish in Nigeria.

Experimental procedure
The experimental ponds were each filled with about 4 m 3 of water after which each of the ponds were stocked with 120 African catfish of post juvenile size giving a stocking density of 30 fish/m 2 .Five fish from each of the ponds were randomly selected and weighed prior to stocking and after every 7 days subsequently.A conscious effort was made to ensure that the post juvenile fish that were stocked in the ponds were almost of the same average weight of 0.3 kg.Water hyacinth was planted to cover about 15% of the surface area of two of the ponds (Pond B1 and B2), while the control ponds (Pond A1 and A2) were left free of water hyacinth.The water hyacinth was placed manually in the pond as required to maintain the percentage cover.The fishes were fed with a commercially available floating feed pellet (SARB) daily.The average feeding rate was 0.33 g per fish per day.At the end of every week, five fishes were selected at random and weighed to determine the fish development.The water in the control ponds was drained and replaced with fresh stream water weekly while that in Ponds B1 and B2 were changed every two weeks as the dissolved oxygen content was found to be too low after the first two weeks.The experiment lasted for four weeks.Before the stocking of the fishes in the ponds, a sample of the water was taken to determine the water quality and the subsequent effect of the water hyacinth on the quality of the fish pond water.Samples of the fish pond water were collected from the ponds around 11.00 am every 7 days using sterilized polyethylene bottles.The samples were stored at 4°C pending when analysis was done.These samples were analyzed for some selected aquatic water parameters.

Physicochemical analyses
The following physicochemical properties were investigated: temperature, conductivity, total dissolved solids, turbidity, pH, dissolved oxygen (DO), ammonia, nitrate, nitrite biochemical oxygen demand (BOD), chemical oxygen demand (COD), total hardness, calcium hardness, magnesium hardness, total alkalinity, chloride, phosphate, sulphate, calcium, magnesium, sodium, and potassium.The selection of these parameters was based on the  (APHA and AWWA, 2012).The specific methods are listed in Table 1.

Temperature
Temperature is the single most important physical factor controlling the life of cold blooded animals.It is critical to growth, reproduction and sometimes survival (Masser, 1997).Figure 1 shows the variations in the temperature of the ponds.The temperature in both the control ponds (Ponds A) and the ponds with water hyacinth (Ponds B) exhibited the same pattern with an average value of 30.88±2.9°C in the control ponds and 30.98±2.72°C in the ponds with water hyacinth during the experimental period.The temperatures were highest during the second week and least during the third.These may have been due to changes in the environmental temperature.Every species of fish has an optimum temperature for growth as well as upper and lower lethal temperatures.
Infonet Biodivision (2016) recommended an optimum temperature of 21 to 27°C for African catfish although this catfish can thrive in warm ponds of up to 33°C (RFP, 2010).Bhatnagar et al. (2004) and Mayer (2012) indicated that a temperature of 25 to 37°C is generally tolerable to fish.Temperature above the optimum range increases the rate of bio-chemical activity of the micro biota and respiratory rate, and so increase in oxygen demand (Bhatnagar and Devi, 2013).
It further causes decreased solubility of oxygen and also increased rate of breakdown of waste and hence increased level of ammonia in water.At the lower temperatures of 15 to 26°C, there is reduced feed intake and decreased growth rate.Fish will not spawn at temperature below 20°C and growth stops at below 15°C (Infonet Biodivision, 2016).The temperature of 28.0 to 34.9°C recorded for the pond with water hyacinth was therefore fairly satisfactory in terms of feed intake, metabolism and growth.With similar range of temperature recorded in both the control ponds and the ponds with water hyacinth, it would appear that water hyacinth had no effect on the temperature of the pond.

pH
The variation of pH in the ponds during the study period is as shown in Figure 2. As with temperature, the pH of the two pond types followed similar pattern.The pH of the control pond was an average of 7.00±0.47,while that of the ponds with water hyacinth was an average of 6.98±0.60.The highest pH values were recorded in the two ponds during the second week.
Water hyacinth has been found to stabilize pH levels and temperature in experimental lagoons, thereby preventing stratification within the water column (Giraldo and Garzon, 2002).Fishes have an average blood pH of 7.4; a little deviation from this value, generally from 7.0 to 8.5, is conducive to fish life and for biological productivity in general.A pH value of 6.5 to 9.0 is generally acceptable for aquaculture ponds (Wurts and Durborow, 1992; Bhatnagar et al., 2004;Santhosh and Singh, 2007;Mayer, 2012, Infonet Biodovion, 2016;Swan, 2017).Fishes can become stressed in water when the pH ranges from 4.0 to 6.5 and from 9.0 to 11.0.Death is almost certain at a pH of less than 4.0 or greater than 11.0 (Ekubo and Abowei, 2011;Bhatnagar and Devi, 2013).The pH values recorded in the two ponds are within acceptable level implying that the use of water hyacinth does not adversely affect the pH of fish ponds.

Hardness
Hardness is a measure of the amount of multivalent cation such as Fe, Ca, Mg, Al, Mn, Zn, etc., present in the sample.Calcium and magnesium are by far the greatest source of hardness in pond water.The mean hardness of the water samples from the ponds are shown in Figure 3.The total hardness increased from the value of 16.00 mg/L at the start of the study to a maximum value of 86.0 mg/L (as CaCO 3 ) by the second week.It subsequently decreased down to a value of 26.0 mg/L by the fourth week.For the pond with water hyacinth, the total hardness increased from 16.0 mg/L at the start of the experiment to a maximum value of 54.0 mg/L by the second week.It dropped to a value 38.0 mg/L  by the third week before rising to 46.0 mg/L at the end of the study.The total hardness in Ponds A and B was an average of 44.75±12.61and 39±15.45mg/L, respectively.The Ca hardness was an average of 19.50±14.27mg/L in the control ponds and 18.00±9.38mg/L in the ponds with water hyacinth while the Mg hardness values were 12.75±4.27and 21.00±11.83mg/L, respectively.
The increase in total hardness may be attributed to the presence of excess unconsumed feed in the water, while the relatively lower values recorded in the ponds with water hyacinth may be due to the absorption of some of the hardness-causing elements in the water by the water hyacinth.
The generally acceptable value of hardness for fish culture is at least 20 mg/L (Swann, 1997) with an optimum range of 30 to 180 mg/L as CaCO 3 (Stone and Thomforde, 2004;Santhosh and Singh, 2007;Swan, 2017).Hardness values less than 20 mg/L causes fish stress while values greater than 300 mg/L is lethal to fish life as it increases pH, resulting in non-availability of nutrients (Bhatnagar et al., 2004).The average hardness values obtained in the two pond types were fairly within the optimum range for fish ponds.The water hyacinth did not significantly affect the hardness of the fishpond water.Also, with the higher magnesium hardness level in the ponds with water hyacinth, it would appear that Mg is relatively less easily absorbed by water hyacinth.

Total alkalinity
Alkalinity is the water's ability to resist changes in pH and is a measure of the total concentration of bases in pond water including carbonates, bicarbonates, hydroxides, phosphates, borates, dissolved calcium, magnesium, and other compounds in the water (Bhatnagar and Devi, 2013).The average total alkalinity in the control ponds was 104.50±56.44mg/L while that of the ponds with water hyacinth was 103±78.12mg/L (Figure 4).An alkalinity value of 75 to 200 mg/L is considered ideal for fish ponds (Wurts and Durborow, 1992), although a range of 20 to 400 mg/L may be acceptable (Stone and Thomforde, 2004;Swann, 2017), For catfish production, the alkalinity must be at least 20 mg/L for good fish pond productivity (Swann, 1997;Steven, 2009;PHILMINAQ, 2017).The alkalinity levels recorded in the two pond types were fairly within the range showing that the water hyacinth had no effect on the alkalinity.In particular, the alkalinity was above the value of 20 mg/L as recommended for African catfish.

Dissolved oxygen (DO)
The principal source of oxygen in water is atmospheric air and photosynthetic planktons (Bhatnagar and Devi, 2013).DO affects the growth, survival, distribution, behavior and physiology of fish and other aquatic organisms (Mayer, 2012).
The DO level in the control ponds (Pond A) was an average of 2.33±1.81mg/L while that of the ponds with water hyacinth was 3.85±3.48mg/L (Figure 5).At the end of the first week, the DO content of Pond B had risen from an initial value of 7.2 mg/L at the start of the experiment to 8.1.By the second week it had gone down to 1.0 mg/L.Despite the necessary change of the water in the ponds at this point, the DO remained at the level of1.0 mg/L until the fourth week when it rose to 5.1 mg/L.For the control ponds, despite the weekly change of the water, the DO level also went down to 1.0 mg/L but by the third week.As noted by Villamagna (2009), dissolved oxygen levels can reach dangerously low levels for fish when large water hyacinth mats prevent light infiltration or when a relatively large area of plants decompose at the same time.Photosynthesis beneath water hyacinth mats is also limited as the plant itself does not release oxygen into the water as do phytoplankton and other submerged  vegetation, resulting in decreased levels of dissolved oxygen concentration (Meerhoff et al., 2003;Troutman et al., 2007;Toft et al., 2003).However, as noted by McVea and Boyd (1975), a water hyacinth cover of up to 25%, does not cause DO to reach levels that threaten fish survival (that is < 2 mg/L).McVea and Boyd (1975) also reported an inverse relationship between dissolved oxygen and water hyacinth cover.
Oxygen depletion in water leads to poor feeding of fish, starvation, reduced growth and fish mortality, either directly or indirectly (Bhatnagar and Garg, 2000).DO level greater than 5.0 mg/L is essential to support good fish production (Bhatnagar et al., 2004).Catfish and other air breathing fish can, however, survive in oxygen concentration as low as 1.0 mg/L (Santhosh and Singh, 2007;Bhatnagar and Singh, 2010;RFP, 2010;Infonet Biodivision, 2016;Swan, 2017).According to Banerjea (1967), DO between 3.0 and 5.0 mg/L in ponds is unproductive.Tropical fishes have more tolerance to low DO than temperate fishes (Bhatnagar and Garg, 2000).
DO level of 1 to 3 mg/L has sub-lethal effect on growth and feed utilization.Although, African catfish and other healthy warm water fish can tolerate 1.0 mg/L DO for short periods of time, they will die if exposure is prolonged (RFP, 2010;Swann, 2017) or grow sluggishly if they survive.Generally, DO less than 1.0 mg/L or greater than 14.0 mg/L can have lethal effect of the fish (Bhatnagar and Devi, 2013).At high DO concentration gas bubble disease may occur (Bhatnagar et al., 2004).
The observed DO values in the two pond types were fairly satisfactory except for the second and third week when it dropped to 1.0 mg/L.Although, as noted by Villamagna (2009), large water hyacinth mat could lead to a dangerously low oxygen level, it would appear that with 15% water hyacinth cover, such low O 2 level may not be attained for a prolonged period of time as long as the water in changed after a maximum period of two weeks.
No mortality was recorded during the study.

BOD 5 and COD
BOD is an indirect measurement of the biodegradable organic matter content of water sample while the COD measures their total organic matter content.The 5-day BOD (BOD 5 ) and the COD of the water samples from the two ponds are shown in Figure 6.With a BOD and COD of 4.1 and 5, respectively, the stream water used in filing the ponds was not free of organic matter.The BOD of the control ponds increased steadily from 30 mg/L at the end of the first week to a maximum of 730 mg/L in the third week before declining to a value of 72 mg/L by the end of the experiment with an average value of 320.83±270.50mg/L.The COD also increased similarly from 35 to 760 mg/L within the same period before decreasing to 231 mg/L.The average value of COD in the control pond was 348.50±306.49mg/L.In the ponds with water hyacinth the BOD rose from 40 to 590 mg/L with an average value of 264.24±257.50mg/L while the COD increased from 46 to 610 mg/L at the third week before declining with an average value of 346.50±256.52 mg/L.The increase in the organic matter content of the pond water may be due to accumulation of unconsumed feed and fish waste discharges in the water.The relatively lower values recorded in the ponds with water hyacinth may be due to the absorption of the organic matter by the water hyacinth.
Clerk (1986) reported that BOD range of 2 to 4 mg/L does not show pollution level of concern while levels beyond 5 mg/L are indicative of serious pollution.The recommended optimum BOD for aquaculture ponds is a maximum of 10 mg/L (Santhosh and Singh, 2007;Bhatnagar and Singh, 2010;Mayer, 2012).The greater the BOD, the more rapidly oxygen is depleted.Although the BOD and COD levels in the ponds with water hyacinth were slightly lower than those of the control, the BOD levels in the two pond types were very high and may have affected the performance of the fish.Perhaps, if the water in the ponds were changed more frequently, the organic matter level may not have been so high.

Cations (Sodium, Calcium, and Magnesium)
The concentrations of sodium, calcium, and magnesium in the two ponds are as shown in Figure 7.The average sodium concentration in the control pond was 3.65±1.23mg/L while that of the ponds with water hyacinth was 3.01±1.45mg/L.The lowest and highest value of sodium concentration was recorded during the second and third week, respectively in both pond types.Sodium (and potassium) is the most important salts in fish blood and are critical for normal heart, nerve, and muscle function (Wurts and Durborow, 1992).The mean concentration of calcium in the control pond was 7.8±5.97,while that of the ponds with water hyacinth was 7.2±3.75.These values are lower than the value of 16.0 to 50.6 recorded by Ehiagbonare and Ogunrinde (2010) when they analyzed water samples from some four fish ponds in Okada, Edo State, Nigeria.Calcium plays an important role in the biological processes of fish.It is necessary for bone formation, blood clotting, and other metabolic reactions (Boyd, 2015).Calcium is also important for egg and larvae development (Stone et al., 2013).The presence of free (ionic) calcium at relatively high concentrations in fish culture water helps reduce the loss of other salts (e.g.sodium and potassium) from fish body fluids.The recommended optimum range of calcium in fish culture water is 25 to 100 mg/L (Wurts and Durborow, 1992;Boyd, 2015).Acceptable range is from 4.0 to 160.0 mg/L (Swann, 2017).Calcium concentration of less than 10.0 mg/L or greater than 350.0 mg/L induces stress on the fish (Bhatnagar and Devi, 2013).
Channel catfish can tolerate low level of mineral calcium in their feed but may grow slowly under such  conditions.The calcium content of both ponds was within tolerable limits.
Magnesium content ranged from 1.9 to 11.0 mg/L in the control ponds with an average value of 4.92±4.29 mg/L.The highest and lowest values occurred during the third and first week, respectively.For the ponds with water hyacinth, the values ranged from 2.9 to 10.0 mg/L with a mean value of 6.95±3.01mg/L.The highest and lowest values also occurred during the third and first week, respectively.The higher concentration of Mg in the ponds with water hyacinth may indicate, as earlier stated, that water hyacinth does not readily absorb Mg.Magnesium is not normally a limiting factor in freshwater aquaculture; it is essential for fish growth, but a specific recommended concentration is not available (Stone et al., 2013).

Anions (Chloride, Phosphate and Sulphate)
Chloride is essential in helping fish maintain their osmotic balance.Chloride content of water is dependent on its salinity level among other factors (Bhatnagar and Devi, 2013).The desirable level of chlorides concentration for commercial catfish production is above 60 mg/L.If the level of chloride relative to nitrite is maintained at the ratio of 10:1, nitrite poisoning, caused by excess nitrite in the pond water and which gives rise to "brown blood" disease in catfish, is eliminated (Stone and Thomforde, 2004).If the chloride level is higher than 100.0 mg/L, it results in the burning of the edges of the gills of the fish with long term after effects (Bhatnagar and Devi, 2013).
The mean chloride levels in the control ponds and the ponds with water hyacinth were 8.5±4.04 and 8.75±6.7 mg/L, respectively (Figure 8).The chloride concentrations in the two ponds were below the optimum level.
Phosphorous is a limiting nutrient needed for the growth of all aquatic and other plants.However, excess concentrations especially in rivers and lakes can result to algal blooms.Phosphates are not toxic to people or animals, unless they are present in very high levels.Digestive problems could occur from extremely high levels of phosphates.Phosphate concentration ranged from 1.9 to 4.36 mg/L in the control ponds with a mean value of 2.66±1.14mg/L.In the ponds with water hyacinth, it ranged from 1.86 to 3.4 mg/L with an average of 2.43±0.71mg/L (Figure 8).A phosphate level of 0.05 to 0.07 mg/L is desirable for optimum production (Bhatnagar et al., 2004;Stone and Thomforde, 2004;RFP, 2010); although Swann (2017) gave a tolerable limit of 0.01 to 3.0 mg/L.The phosphate concentration in the ponds was relatively high and could result in excess vegetative growth.This was however not noticed in the experimental ponds.
Sulphate (SO 4 ) is a naturally occurring compound in surface and ground waters.Concentrations can range naturally from 0 to 1,000 mg/L.Fishes have a wide range of tolerance for sulphate.The mean sulphate level in the control ponds was 17.25±4.57mg/L, while that of the pond with water hyacinth was 18.75±5.38mg/L (Figure 8).These are within the acceptable limits.

Nitrogen
Nitrogenous organic wastes come from uneaten feeds and excretion of fishes.Ammonia-Nitrogen (NH 3 -N) is the primary nitrogenous waste produced and excreted by fish in a fish pond.Thus, the concentration of ammonia-N is positively correlated to the amount of food wastage and the stocking density (Bhatnagar and Devi, 2013).The average ammonia concentration was 16.9±13.46mg/L in the control ponds and 14.33±11.76mg/L in the ponds with water hyacinth (Figure 9).The unionized form of ammonia (NH 3 ) is extremely toxic while the ionized form (NH 4 + ) is generally harmless and can dissipate into the atmosphere easily (RFP, 2010;Bhatnagar and Devi, 2013).Ammonia concentration below 0.02 mg/L is considered safe (Swann, 1997(Swann, , 2017)); for short term exposure NH 3 level of 0.6 to 2.0 mg/L can be tolerated in fish pond (Robinette, 1976).High ammonia concentration (>0.1 g/mL) causes an increase in pH and ammonia concentration in the blood of the fish.This can damage gills and red blood cells, destroy mucous-producing membranes, affect osmo-regulation and reduce the oxygen carrying capacity of the blood while increasing the oxygen demand of the tissues (Lawson, 1995;Bhatnagar and Devi, 2013).It can also reduce growth and results in poor feed conversion.Fish suffering from ammonia poisoning generally appear sluggish or often at the surface gasping for air (Bhatnagar and Devi, 2013).However, the level of ammonia toxicity depends on the fish species, water temperature and pH (Masser, 1997); its toxicity increases with an increase in temperature and/or pH, with pH being the most important factor (RFP, 2010).With NH 3 levels of up to 33.0 and 25.0 mg/L recorded, respectively in Ponds A and B, it is obvious that the fish suffered from ammonia toxicity.However, as stated earlier, no mortality was recorded during the study.
Nitrite (NO 2 ) is an intermediary product which results from the conversion of NH 3 or NH 4 + into nitrate (NO 3 ).Like ammonia, nitrite is highly toxic to fish.It oxidizes haemoglobin to methemoglobin in the blood, turning the blood and gills brown and hindering respiration (Lawson, 1995;Bhatnagar and Devi, 2013).It also damages the nervous system, liver, spleen and kidneys of the fish.The level of toxicity depends on chemical factors such as the reduction of calcium, chloride, bromide, and bicarbonate ions and levels of pH, dissolved oxygen, and ammonia.The desirable level of nitrite in pond water should be 0 to 1.0 mg/L (Bhatnagar et al., 2004;Stone and Thomforde, 2004;Mayer, 2012).However, a concentration of less than 4.0 mg/L is acceptable (Stone and Thomforde, 2004;Swann, 2017).The nitrite concentration recorded ranged from 0.01 to 0.56 with an average of 0.15±0.27mg/L in the control pond.In the pond with water hyacinth, it ranged from 0.01 to 2.95 with an average of 0.81±1.43mg/L (Figure 9).These are fairly within acceptable level.As with other parameters, the water hyacinth did not seem to affect the nitrite level in the ponds.
Nitrate (NO 3 ) is formed through nitrification process, that is, oxidation of NO 2 into NO 3 by the action of aerobic bacteria.The mean nitrate concentration recorded 8.6±5.63 mg/L in the control ponds and 23.2±17.47mg/L in the ponds with water hyacinth (Figure 9).Nitrate is generally stable over a wide range of environmental conditions and is highly soluble in water.Compared with other inorganic nitrogen compounds, it is relatively nontoxic (Stone and Thomforde, 2004).However, high levels can affect osmoregulation, oxygen transport, eutrophication and algal bloom (Lawson, 1995).The desirable concentration of nitrate in fish culture water is 0.1 to 4.0 mg/L (Santhosh and Singh, 2007); a concentration of 0 to 200.0 mg/L is however acceptable (Meck, 1996;OATA, 2008;Bhatnagar and Devi, 2013).The nitrate levels recorded in the two pond types are within acceptable level.

Conductivity and total dissolved solids (TDS)
Conductivity is a measure of the ability of water to pass an electrical current.It is an index of the total ionic content of the water and is affected by the presence of inorganic dissolved solids anions such as chloride, nitrate, sulfate, and phosphate; or cations such as sodium, magnesium, calcium, iron, and aluminum.It also depends on the temperature and variation in the total dissolved solid in the water (Bhatnagar and Devi, 2013).The desirable range of conductivity in pond fish culture is 100 to 2000 µS/cm; a range of 30 to 5000 µS/cm is however acceptable (Behar and Montpelier, 1997;Stone and Thomforde, 2004).Some aquaculture species, such as channel catfish, can tolerate levels as high as 30,000 µS/cm (Austin et al., 2016).
The mean conductivity in the control ponds was 221.75±81.75µS/cm (at 25°C) while that of the ponds with water hyacinth was 234.0±134.84µS/cm (Figure 10).This is similar to the values of 117.3 to 378.4 µS/cm recorded by Keremah et al. (2014) when they analyzed water samples from freshwater fish ponds in Bayelsa State, Nigeria.Total Dissolved Solids (TDS) includes those materials dissolved in the water, such as, bicarbonate, sulphate, phosphate, nitrate, calcium, magnesium, sodium, organic ions, and other ions.These ions are important in sustaining aquatic life.The recommended level of TDS concentration in freshwater aquaculture environment is 500 to 1200 mg/L (Sarkar, 2002;Keremah et al., 2014;PHILMINAQ, 2017).High level of concentrations can result to damage in organism's cell (Mitchell and Stapp, 1996), water turbidity, reduce photosynthetic activity and increase the water temperature.The mean TDS concentration in the control ponds was 132.5±48.89mg/L, while that of the pond with water hyacinth was 140.4±81.0(Figure 10).The dissolved solid contents of both ponds were fairly low.Also, from the graph, it can be seen that there is a clear relationship between TDS and conductivity.

Turbidity
The turbidity in the control ponds ranged from 36.9 to 106.0 NTU with an average of 62.28±31.42NTU while that of the pond with water hyacinth ranged from 48.8 to 70.0 with an average of 63.7±10.11NTU.The water in the control ponds was slightly less turbid.Turbidity is a measure of the ability of the water to transmit light.Inability to transmit light may be caused by suspended clay particles, dispersed plankton organisms, particulate organic matter and pigments caused by decomposition of organic matter.Turbidity caused by suspended solids in the water restricts light penetration, limits photosynthesis, and inhibits algal growth and therefore oxygen production.Clay turbidity in water of 30 cm or less may prevent development of planktons blooms (Boyd and Lichtkoppler, 1979).Turbidity range of 30 to 80 cm is good for fish health, 15 to 40 cm is good for intensive culture system, while values less than 12 cm causes stress (Bhatnagar et al., 2004).A value of 30 to 40 cm is considered optimum for a good fish culture (Santhosh and Singh, 2007).Turbidity levels as low as 5 NTU can begin to stress fish within a few hours (VWF, 2017).The turbidity values of the ponds were fairly high.

Growth rate of the fish
There are many factors that impede/facilitates the growth rate of any living organism, catfish is not an exception.Figure 11 shows a comparison of the growth rate of the fishes in the pond with and without (control) the introduction of water hyacinth (E.crassipes).
The initial average weight is represented in week 0, while weeks 1 to 4 show their progressive growth rate.At 0 week, the fishes in both ponds had about the same average weight of 0.3 kg.At the end of the first week (Week 1), the average weights of the fish in both ponds were about the same (about 0.34 kg) each.At the end of the second week (Week 2), the average weight of the fish in pond B was slightly greater than that of A. In week 3, the pond B (with water hyacinth) recorded higher growth rate than that of the control ponds.By the 4th week, the growth rate of the fishes in pond B (with water hyacinth), were far higher than that of the control ponds.
The average weights of the fish in Ponds A and B were about 0.69 and 0.85 kg, respectively implying that the use of water hyacinth could lead to larger fish size.This agrees with the study of Velasco and Cortes (2005) who, working with tilapia, observed that increasing plant cover resulted in the production of larger fish.Although the final average weight of the fish in the ponds with water hyacinth was higher than that of the control; the difference was not significant (P≤0.05)implying that covering some 15% of the surface of fish ponds used for raising African catfish may not be a worthwhile exercise.

Analysis of variance (ANOVA)
Table 3 shows the result of the ANOVA carried out on the experimental result.The table shows that, although there were some differences in some of the parameters monitored in the control ponds and the ponds with water hyacinth, these differences were not significant at 5% αlevel (P < 0.5).

Figure 1 .
Figure 1.Variation of temperatures in the ponds during the study.

Figure 2 .
Figure 2. Variation of pH in the ponds during the study.

Figure 3 .
Figure 3. Total, Mg and Ca hardness of the water in the ponds during the study period.

Figure 4 .
Figure 4. Variation of alkalinity in the ponds during the study.

Figure 5 .
Figure 5. Variation of DO in the ponds during the study.

Figure 6 .
Figure 6.BOD5 and COD concentration in the two ponds during the study.Pond A = Control; Pond B = Pond with water hyacinth.

Figure 7 .
Figure 7. Mean concentrations of sodium, calcium and magnesium in the two ponds during the study.Pond A = Control; Pond B = Pond with water hyacinth.

Figure 8 .
Figure 8. Anion concentrations in the fish ponds.

Figure 9 .
Figure 9. Mean nitrogen concentration in the control ponds (Pond A) and the ponds with water hyacinth (Pond B).

Figure 10 .
Figure 10.TDS and conductivity values recorded in the ponds during the study.

Figure 11 .
Figure 11.Fish growth rate in pond with and without (Control) water hyacinth (Eichhornia crassipes).

Table 1 .
Method employed in the physicochemical analyses.