Optimization of induced breeding of Clarias gariepinus using different sources of water

Ataguba Gabriel Arome, Okomoda Victor Tosin and Ukpong Prince

Department of Fisheries and Aquaculture, Federal University of Agriculture, P.M.B. 2373, Makurdi, Benue State, Nigeria
gabriel.ataguba@uam.edu.ng

Abstract

The effect of four different water sources (rain, borehole, river and tap) on hatching of African Catfish (Clarias gariepinus) eggs as well as early survival of fry was investigated using induced breeding with the determination of fertilization, hatching and survival rates. Higher hatchability (p<0.05) was observed in eggs incubated in river water (66.6%) while the lowest hatch was observed in eggs incubated in borehole water (12.7%). High larval survival (98%) was observed for fry held in River water while the lowest survival (55%) was observed when fry were held in borehole water. Similarities (p>0.05) were observed in temperature, pH and DO among different water sources, but conductivity, total dissolved solids (TDS) and water hardness were not similar (p<0.05). Hatchability and survival are negatively correlated (p<0.05) with conductivity, water hardness and TDS. Optimization of water sources for hatchability using the water quality parameters revealed that the use of river water with hardness of 12.8mg.l^-1 at a temperature of 26.4°C will give an optimal hatchability of 71.6%.

Keywords: catfish, eggs, hatching, survival, water hardness

Introduction

Among the culturable food fish in Nigeria, the African Catfish, Clarias gariepinus is most desirable in high value Nigerian markets (Suzette et al 2021). The catfish is very important to the sustainability of the aquaculture industry in the country. However, in spite of the break through reported for its artificial propagation (Madu and Offor 2005), the demand for fish seed still outstrips the supply. The problem of inadequate supply of fish seed can only be solved through induced breeding by the application of various inducement materials. Various fish have been induced to spawn, using various hormonal materials (Legendre et al 2000; Ameti 2019). However, under several experimental conditions, hatchability and survival of fry and fingerling is never 100%, hence there is need for research to understand the reasons behind breeding failures if the overwhelming demands of fingerlings of African catfish is to be met.

One of the most difficult aspects of aquaculture is husbandry during the early life stages. The most sensitive stage in the life cycle of a teleost is generally considered to be the developing egg and larva (Valdes et al 1991; Olaniyi and Omitogun 2014). The failure as well as successful rearing of any fish is partly dependent on water quality (Chatakondi 2019). Generally, research in the past have isolated some individual water quality parameters and evaluated their effects on embryonic stages of fish. The effects of salinity (Fafioye 2001) and water temperature (Abolagba 1999) on larval development and survival of Clarias gariepinus have been reported. Another water quality parameter having a major effect on egg development, and egg and larval survival is water hardness (Tucker and Steeby 1993; Spade and Bristow 1999). Bart et al (2013) reported that tilapia yolk sac larvae and swim-up fry survival decreased with increase in salinity and increased with increase in water hardness.

Climate change affects water quality and this translates to an effect on aquaculture with changes in water quality that can either impact positively or negatively on performance of species under culture (Maulu et al 2021). Generally, the value of physicochemical parameters in water sources used for fish hatching differs from one source to another, more so, different fish species exhibit different tolerance limits to physicochemical properties such as hardness, pH, dissolved oxygen etc. Sources of water supply for hatchery include rivers, reservoirs, springs, creeks, lakes and boreholes or deep wells (Akankali et al 2011). The effect of water from different sources on hatching success of the African catfish (Clarias gariepinus) eggs is hereby investigated in relation to the water quality parameters of the water from the different sources.

Materials and methods

Fish maintenance, water sources, hormonal treatment and artificial fertilization of eggs.

Broodstock of about one year old were obtained from the Fisheries research farm of the University of Agriculture Makurdi. The broodstock were maintained for two weeks in concrete tanks at the hatchery unit and fed 35% crude protein pelleted feed at 5% of the biomass daily.

Water from four different sources were used for the present study namely: rain water, borehole water (sourced within University of Agriculture Makurdi), river water (collected from the bank of River Benue at Department of Fisheries and Aquaculture teaching and research farm) and tap water (collected from the tap water reservoir of the Department of the Fisheries and Aquaculture). All the water were collected the same day except for rain (which was collected over a period of two weeks) and kept in 50 litre bowls for the experiment.

Broodstock were induced with ovaprim^® at a dosage of 0.5ml per body weight(g) to trigger oocyte maturation and ovulation. Hormone administration was carried out via intramuscular injection. After a latency period of twelve hours, the eggs were collected from each female by gently pressing the abdomen of the fish. These were collected into a clean bowl. The weights of the egg were determined as well as fecundity. Milt was obtained by surgical removal of the testes from the males and used to fertilize the eggs accordingly. The stripped eggs were mixed with the milt gotten from the male after which 5 ml of water from each water source was added to create the treatments. After gently and thoroughly stirring, the eggs were transferred and incubated in replicate 60L capacity plastic aquaria using nylon type mosquito mesh netting as substrate. Water volume was maintained at 50 litres for all treatments. Eggs were incubated in this static condition with aeration at an ambient temperature between 27 to 29°C. Hatching was observed to be complete between 24 to 28 hours after fertilization, and the hatching rates were evaluated about 4 hours later.

Determination of fertilization and hatching rate

A known mass of egg that was not inseminated was used to determine fertilization. The time taken for these control eggs to become opaque (dead eggs) was noted, after which the brownish/greenish eggs in the test bowls were termed as fertilized. The number of eggs spawned was calculated by weighing 1g of eggs from each female (triplicate determinations were made). The number of eggs in one gram was determined by counting and the average of the three counts was taken as the number of eggs in 1g of eggs. The total weight of eggs spawned for each female was noted and this was multiplied by the average number of eggs already determined in the present study. Fertilization rate was determined using the method described by Ella (1987) as previously described in Ataguba et al (2009).

The hatching rate of each cross was evaluated 32 hours after fertilization. The number of hatched larvae was determined using the volumetric method as described by Ella (1987). Three hundred larvae were counted using a fine mesh dip net and placed in a graduated measuring cylinder already filled with known volume of water with care being taken to avoid adding extra water along with the larvae. The change in water level after adding the larvae was noted. Afterwards, all the larvae were placed in a graduated measuring cylinder and the level of water change recorded. The total number of larvae in each case was determined using the equation:

Determination of survival rate

The survival rate was determined as the number of fry at the start of exogenous feeding or post yolk sac absorption. Small aliquots of water (500ml) with fry within were taken for each replicate per treatment and larvae were counted by collecting them from the aliquot using a plastic spoon until all fry were counted.

Data analysis

Data collected were analyzed using Genstat Discovery edition and Minitab 14. Fecundity, fertilization and hatching rates of the different treatments were compared using one-way ANOVA followed by Fisher’s LSD to determine significant differences among means. Analysis of covariance (ANCOVA) was used to determine water quality parameters that can be utilized in optimizing conditions for the most suitable water source. After this, a response surface analysis was carried out to determine the optimal water quality conditions. These tests were performed using Minitab 14.

Results

Fertilization rates (Table 1) of eggs mixed with milt using the different water sources were similar (p>0.05). Hatching rates were not similar (p<0.05) as eggs incubated in river water hatched gave the best hatching rate (67%) while eggs incubated with borehole water gave the least hatching rate (13%). Similarly, survival rate was highest (p<0.05) for fry raised in river water (98%) while only 55% of fry raised in borehole water survived. Result of the correlation between water quality and breeding parameters (Table 2) reveals that fertilization rates were not influenced by water quality parameters. Hatchability correlates (p<0.05) with survival, hardness, conductivity and TDS. The correlation between hatchability and survival is a strong and positive correlation (r = 0.94) but hatchability correlates negatively with hardness (-0.9), conductivity (-0.9) and TDS (-0.9). Survival rates were correlated ( p<0.05) with hardness (-0.95), DO (0.75), conductivity (-0.9) and TDS (-0.9). The mean water temperature, dissolved oxygen and pH of different water sources (Table 1) in the incubation tanks during the experiment were similar (p>0.05). However, mean electrical conductivity (µS.cm^-1) was higher (p <0.05) for borehole water (1145µS.cm^-1) compared to river (114µS.cm^-1), rain (107µS.cm^-1) and tap water (97µS.cm^-1). Total dissolved solid also followed the same trend (p<0.05) with 573mg.l^-1; 57mg.l ^-1, 53mg.l^-1 and 49mg.l^-1 obtained from borehole water, river, rain and tap water respectively.

Optimization of Hatchability

The various water sources when considered individually can lead to an increase in hatchability at various degrees of effectiveness (Table 3). Borehole water has the least (p=0.05) increasing factor (11.8%) while river water has the highest level of contribution (42%) to increase in hatchability. The ability for rain water to increase hatchability is tending towards a noteworthy one (p=0.053). Higher levels of water hardness are associated with lower hatchability (Figure 1) and higher temperatures as associated with the water sources elicit better hatchability.

The optimized water source was river water (Table 4) with a hatchability level of >71% at 12.8mg.l^-1 level of water hardness and a temperature of 26.4°C.

Discussion

Fertilization rates of the eggs incubated in the different water sources were not significantly different (p>0.05). This is because fertilization is basically a function of egg viability (Dettlaff, et al 2012), sperm quality (Mansour et al 2005) and time lapse between stripping and insemination (Yang and Chen 2006). de Graaf et al (1995) reported an average hatchability of 59.1% for C. gariepinus in the republic of Congo, while Macharia et al (2004) reported a rate as low as 4% for C. gariepinus eggs on a nylon substrate. This however is very low compared to the outcome of the present study even though nylon net was used as hatching substrate. It is however necessary to acknowledge the fact that differences that arises from breeding history, age and water quality can affect hatching rate. According to Fyhn et al (1999) low salinity and water hardness heightens the increase in egg diameter because the swelling process of flaccid newly shed eggs is higher when they first contact water and absorb water. This implies that lower levels of water hardness may elicit poor hatchability if the milt is not properly mixed with the eggs before addition of water. The observation in this study shows that hatchability increased with reduction in water hardness. This could be attributed to proper zygote formation and exocytosis that leads to egg hydration and embryo formation (Rizzo and Bazzoli 2020) at lower levels of water hardness (Chapman and Deters 2009). There was also a strong (p<0.05) negative correlation between hatchability and hardness. According to Tucker and Steeby (1993), a water hardness level that does not exceed 10mg.l^-1 is ideal for channel catfish egg incubation and nursing while water hardness has been reported to have no effect on hatchability of bighead carp (Chapman and Deters 2009). Similarly, increase of waterborne Ca⁺² above 20mg.l^-1, irrespective of water hardness is deleterious for incubation of silver catfish eggs because it reduced post-hatch (2 days after hatching) survival and larval weight and length after 21 days (Silvaet al 2003; Silvaet al 2005). Apparently, effect of water hardness varies according to life stage, species and water quality (Baldisserotto 2011). However, the effects of TDS seem to be uniform among fish species. Very high values of TDS (>2000mg. ^l-1) have been reported as having no effect on hatching, growth and survival of several fish species (Chapmanet al 2000; Scannell and Jacobs 2001). However, the present results indicate that TDS correlates negatively with hatchability and fry survival.

Considering their size, fish embryos and larvae are susceptible to many types of organic and inorganic materials dissolved or suspended in the water, such as gases, minerals, metals and particulate matter from rocks, soil, plants, atmosphere and animals (Brix et al 2010). Correlation of TDS with survival rate was negative (p<0.01) showing that higher TDS leads to lower survival rates. Therefore, survival was higher for fry raised in river water, rain water and tap water than borehole water. This probably suggests that the effect of TDS on survival is acute rather than chronic since it elicits mortality that approached 50% within 4 days.

Generally, under the same experimental conditions (atmospheric temperature, humidity and artificial aeration), water from different sources are likely to have similar value for parameters such as temperature and dissolved oxygen. According to Boyd and Tucker (1998), the pH of most freshwater culture facility remains within 6.0–9.0 range, and usually there is a daily fluctuation in pH of one or two units. The highly negative (p>0.05) correlation between water pH from the different sources with hatching and survival suggests that there is negative effect of pH on these parameters but it is not noteworthy. According to Reynalte-Tatajeet al (2015), a pH of 7.0 is ideal for larval survival while a pH reduction from 8.5 to 7 elicits better growth. The pH of the water from the four water sources were similar and slightly below 7 but not so low as to be classified as very acidic. The low (below 7.0) values of pH are therefore responsible for the negative correlations of pH with survival and hatching. Dissolved oxygen, pH, and Temperature levels recorded in the present study were in the range for optimum growth of teleosts according to Boyd and Tucker (1998), however, the fact that Dissolved oxygen and pH were not remarkably correlated with the breeding parameters justified the thought that they had no influence on the outcome of the present study, the highly negative and (p>0.05) correlation of temperature with hatching might be explained by the fact that within a threshold or range, increase or decrease in temperature leads to increased or reduced hatchability. Tolerance limit of temperature for the development of C. gariepinus eggs was established by Haylor and Mollah (1995) to be 20-30°C. Hatchability of Heterobranchus bidorsalis was optiman between 28-30°C with survival rates being higher at 28°C compared to 26°C (Okunsebor et al 2015). The current results suggest that 26°C is not deleterious to survival but results of hatchability under the various water sources and their temperature regimes is in fact modulated by three other water quality parameters namely water hardness, conductivity and TDS. The latter parameters are indeed related and can be derived mathematically (Rusydi 2017).

The optimization algorithm has shown that river water is ideal for hatchery incubation of C. gariepinus eggs at a hardness level of 12.8mg.l ^-1. This confirms the earlier report by Tucker and Steeby (1993) that a minimum hardness level of 10mg.l^-1 is ideal for incubation of catfish embryos. In addition, the optimized temperature of 26.4°C is within the range that leads to hatching within 24 hours of incubating embryos of the African catfish (de Graaf and Janssen 1996). The pattern of temperature and hatchability being directly proportional has earlier been demonstrated (Haylor and Mollah 1995).

Conclusions

• Though borehole water gave a good fertilization rate, care should be taken on the use of this source of water for incubation, hatching and nursing due to the fact that high TDS could lead to fry mortality at a later stage.
  
  
• River water performed well in fertilization, hatching and survival of larvae but may pose danger in hatcheries due to possibility of disease transmission from the wild as well as uncertainties associated with climate change.
  
  
• Among all water sources, rain water performed the least in fertilization while tap water performed poorly in hatching behind borehole water.
  
  
• There is some level of intolerance for borehole water, rain water and tap water during incubation but this is overcome at the larval nursing stage with water from rain, the river and the tap but not from the borehole.

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