Water Quality Effects on Growth and Survival of Oreochromis jipe and Oreochromis niloticus Species in Aquaculture

Abstract

The study was conducted at Kegati Aquaculture Center (KMFRI) for 12 weeks to evaluate the effect of water quality parameters on the growth and survival rates of Oreochromis jipe and Oreochromis niloticus. The fingerlings (n = 270), were stocked in triplicates in 9m2 raised ponds arranged in double series and fed on a 30% CP ration twice a day at 10% total bodyweight. Water quality parameters were measured daily using the YSI multi-parameter meter. Fish total length and bodyweight was determined biweekly using a measuring board and a digital weighing balance, respectively, and survivals were determined from the initial and final counts of fingerlings. Data were analyzed with an unpaired sample t-test using R-software and statistical significance was considered at p < 0.05. Temperature, total dissolved solids (TDS), and salinity showed no significant differences, whereas the pH and dissolved oxygen (DO) levels were significantly different (p < 0.05) between the O. jipe and O. niloticus. Furthermore, O. jipe attained a lower final mean weight (12.16 ± 0.34 g) compared to O. niloticus (29.79 ± 0.91 g). The study recommends a further study be conducted in a controlled culture environment to establish optimal conditions for O. jipe culture.

1. Introduction

Water quality encompasses all environmental and, to some extent, biological factors affecting fish growth, survival, and ecology. The most commonly monitored physicochemical parameters include temperature, pH, turbidity, dissolved oxygen concentration (DO), total dissolved solids (TDS), electrical conductivity, and total suspended solids [1]. Temperature controls dissolved oxygen (DO), pH levels, and chemical processes in water. Optimum temperature speeds up fish metabolic rates, which in turn increases feed consumption to meet the energy demands, while high temperature and pH increase the ammonia toxicity to aquatic organisms [2, 3]. Temperature also increases the rate of decomposition and affects feed digestion and assimilation efficiencies in living organisms. The optimum temperatures range for warm water fish (20–30°C) results in maximum growth and survival of these organisms [4]. The lower and upper lethal limits for tilapia are 10–11°C and 37–38°C, respectively [5].

Water pH and DO concentrations regulate the general metabolism and many physiological processes in the cultured fish, such as nitrite and ammonia toxicity. Most aquatic organisms perform optimally in DO levels ranging between 5 and 9 mg L⁻¹, while the DO concentrations below 3 mg L⁻¹ and above 9 mg L⁻¹ are detrimental to aquatic life [6]. Although tilapias are highly tolerant to low DO levels, O. niloticus can survive short-term exposure to low DO levels of 0.1 mg L ⁻¹ [7], the optimum performance of the species only occurs at DO concentrations ranging between 4.2 and 5.9 mg L⁻¹.

Tilapia have been reported to tolerate a range of up to 3.7 and 11.0 pH but the recommended optimum pH range for most tilapia species is 6.5 to 9.0 [7, 8]. Deviations above or below this optimum range for the species are likely to bring about behavioral and physiological adjustments, which affect the growth performance and survival as fish try to adapt to stressful pH conditions. The highest and lowest lethal pH limits for most fish species are 3.7 and 11.0 respectively [8]. Low pH decreases the egg hatchability rates, while massive fish mortalities occur due to prolonged exposure to toxic un-ionized ammonia whose concentration increases to concentrations greater than 50% when the pH is greater than nine. Ammonia concentrations higher than 0.2 mg L⁻¹ are detrimental to fish and are known to depress the appetite of tilapia [5].

2. Materials and methods

2.1 Study area

The study experiment was conducted for 12 weeks from September to December 2019 at Kenya Marine and Fisheries Research Institute (KMFRI), Kegati Aquaculture Center.

Kegati Aquaculture Center is located in a high-altitude area (1974 m asl) between latitudes and longitudes 00420 50.44’S and 0344 470 59.4’E as shown in Figure 1. The center receives an averagely high rainfall amount of 1800 ± 100 mm per annum and has a mean temperature range of 20.3–23.9^°C. It is drained by river Kuja with a total catchment area of 5180 km² [9]. The sampling stations were selected based on accessibility, availability of a well-equipped hatchery facility, and technical support for the study.

Figure 1.

Map of the study area at KMFRI – Kegati aquaculture research Center in Kisii County, Kenya.

Six raised wooden ponds measuring 9m² in a double series and a regular arrangement were randomly assigned to the two treatments in three replicates. The ponds were filled with screened un-chlorinated spring water through an independent inlet to 0.6 m level and water exchange was provided through an outlet throughout the study to promote aeration and siphoning of wastewater containing feed remnants, bioflocs, and fecal waste at 4 days interval. The mixed-sex O. niloticus and O. jipe fingerlings with an initial mean weight of 2.93 ± 0.12 g and 2.69 ± 0.10 g, respectively, were stocked in the raised wooden ponds at a stocking density of 5 fish m-3.

The fingerlings were fed on 1 mm commercial floating pellets with 30% CP. The daily ration was divided into two equal portions, which were fed regularly to fish twice a day between 0930 h and 1500 h EAT time throughout the study period as recommended by ref. [10]. Fish feed administration was done manually which enabled regular inspection of the individual fish and close monitoring of the feeding process, and identifying any dead fish in the pond, which was immediately removed, and the number of mortalities recorded. The feeding rate was at 10% per calculated bodyweight of all fish but the daily ration was divided into two halves for feeding the fish in the morning and afternoon.

2.2 Data collection

Fish growth performance was assessed using average and cumulative bodyweights, which were taken progressively on fingerlings sampled from each raised pond at the end of every 2 weeks. A digital electronic balance (TX 4202 L, SHIMADZU - Corporation, Philippines) with a precision level of 0.01 g was used to record bodyweights. The fish were starved for 24 hours before sampling. Sampling was done very early in the morning before 0900 h to reduce handling stress, which can cause mortality of fingerlings. A sample of 30 fish per tank was taken randomly from each raised pond using a 0.5-inch scoop net. The fingerlings were weighed and returned to their respective ponds. The fingerlings were blot-dried using filter paper before weighing as recommended by ref. [11] and the measurements were taken inside the hatchery to avoid the effects of wind on the digital weighing balance [12]. The fish total length was measured using a graduated board with a readability of 0.1 cm.

After taking both total length and bodyweight measurements, the fingerlings were immediately returned to their respective labeled raised wooden ponds and no feeding was administered until the fingerlings completely recovered from handling stress and were observed freely swimming in the pond. Any sick fish noticed was removed and given prophylactic treatment using 5% sodium chloride solution before returning it to the pond. This was when feeding was administered according to the experimental design. The progressive length-weight measurements were taken biweekly inside the hatchery to avoid the effects of wind on the digital balance [12] and the adjustment of the feeding rates for the fingerlings was done accordingly. Fish survival was determined by counting all stocked fingerlings in each replicate at the start and the end of the growth experiment. After recording the total length and bodyweight, the fingerlings were restocked in their respective culture ponds and feeding resumed after they were observed to have recovered from stress.

The physicochemical parameters determined during the study were DO (mg L⁻¹), temperature (°C), pH, conductivity (μS cm⁻¹), TDS, and salinity. The measurements were regularly taken during the morning hours between 10 am and 11 am throughout the week before the fish were fed their normal daily ration. The water level was maintained at 0.6 m and all previous feed remains were removed before new feeding was administered. Water quality variables: temperature, pH, dissolved oxygen (DO), salinity, conductivity, and total dissolved solids were recorded using the YSI multi-parameter meter (H9829 model), by taking the readings thrice and finding the average. The samples for water physicochemical parameters were collected daily in triplicates and analyzed according to standard methods described by the American Public Health Association [13].

2.3 Data analysis

The collected data were tested for normality using the Shapiro–Wilk test [14], and homogeneity of variances using Bartlett’s test. Data were normally distributed and variances homogenously spread, therefore, an unpaired sample t-test was used to compare the population means of O. jipe and O. niloticus treatments. The variations in observed datasets on growth performance, survival rates, and the water quality variables were compared between O. jipe and O. niloticus treatments using robust mean ± standard error and range and nonrobust mean ± standard deviation using the R-software programming procedures [15]. All data analyses were performed using the 64-bit R-software version 3.6.3 [15], and the observed differences were considered statistically significant at p < 0.05.

2.4 Determination of growth and survival rates

The fish growth and survival parameters were computed with the following equations according to [10]:

$$\text{Specific growth rate}\left(SGR\right)\%/day=\frac{InWt-InW0}{t}\times 100$$E1

$$\text{Feed conversion ratio}\left(FCR\right)=\frac{Consumedfeed\left(g\right)}{W1-W0}$$E2

where W0 and W1 are the initial fish weight and the final fish weight (g) of the fingerlings, in is the natural logarithm, and t is the number of culture days.

$$\text{Survival rate}\left(\%\right)=\frac{finalfishcount}{initialfishcount}\times 100$$E3

$$Net\text{yield}\left(kg{\text{m}}^{-3}\right)=\text{Harvest biomass}–\text{Stocking biomass}$$E4

3. Results

3.1 Fish growth, survival, and production parameters

The general growth trend showed that there was a steady gain in bodyweight in both O. jipe and O. niloticus during the study period. The un-robust comparisons of combined boxplots and standard deviations show a wide variation in data recorded from the two treatments. The mean, standard deviations, and variance of fish bodyweights in O. niloticus and O. jipe exhibited a wide range of variation and increased exponentially during the culture period (Figure 2). The means and standard error variations for the growth, survival, and production indices of O. jipe and O. niloticus treatments are shown in Table 1.

Figure 2.

Data variation in Oreochromis niloticus and Oreochromis jipe using a comparison of boxplots and non-robust mean +/− SD.

Parameter	O. niloticus		O. jipe		n	t - test sig.
	Mean ± SE	Range	mean	Range
Initial length (cm)	4.80 ± 0.39	2.4–7.1	4.67 ± 0.17	1.82–7.85	180	p = 0.23
Final length (cm)	11.51 ± 0.33	8.1–16.7	9.11 ± 0.72	6.5–12.0	179	p = 0.01
Initial weight (g)	2.93 ± 0.25	0.61–5.64	2.69 ± 0.20	0.82–5.05	180	p = 0.14
Final weight (g)	29.79 ± 0.91	17.7– 55.2	12.16 ± 1.34	6.78–22.39	179	p < 0.05
SGR (gfish^−1 day^−1)	2.28 ± 0.21	0.36–3.76	1.45 ± 0.74	0.12–4.74	170	p < 0.05
%Weight Gain (gfish^−1).	4.32 ± 0.32	2.51–5.67	1.58 ± 0.35	0.98–2.73	170	p < 0.05
DWG (gfish^−1 day^−1)	0.32 ± 0.17	0.11–0.96	0.113 ± 0.01	0.07–0.17	170	p < 0.05
FCR	1.59 ± 0.12	1.21–1.68	2.502 ± 0.15	2.35–2.57	12	p = 0.02
Survival rates (%)	96.28 ± 0.95	94.6–100	92 ± 1.19	74.6–95.0	35	p = 0.02
Fish yield (kgm^−3)	2.59 ± 0.05	2.79–3.15	0.85 ± 0.03	0.79–0.99	170	p < 0.001

Table 1.

Mean (± standard error) of growth, survival and production parameters for Oreochromis jipe and Oreochromis niloticus.

3.1.1 Survival rates

Both species recorded high survival rates ranging between 74.6% and 95% in O. jipe treatment, while in O. niloticus, it ranged between 94.6% and 100%. Hence, the mean survival rate in O. jipe (92 ± 1.19%) was significantly lower (p < 0.05) than the mean survival rate (96.28 ± 0.65%) of O. niloticus treatment. Whereas, O. niloticus maintained high survival rates throughout the culture period, the lowest survival rates were recorded in O. jipe treatment due to mortalities that occurred during the culture period.

3.1.2 Growth parameters

The observed fish growth in terms of bodyweight indicated both species were initially growing slowly during the first few (1–3) weeks of the culture of the study but increased exponentially after the second month. The highest and lowest fish total lengths observed during the final sampling were (16.7 cm and 6.5 cm) in O. niloticus and O. jipe, respectively. However, despite this wide range of variation observed in the total length measurements, the two-sample t-test indicated no significant growth difference (p > 0.05) between the mean final length (TL = 11.51 ± 0.13 cm) of O. niloticus and O. jipe (TL = 9.11 ± 0.12 cm).

The mean growth in final bodyweight in O. jipe (12.18 ± 35 g) was significantly lower (t = 2.42, p < 0.05) than the mean final weight (29.79 ± 0.91 g) for O. niloticus (Figure 3). Similarly, there was a significant difference (t = 2.57, p < 0.05) in the SGR between the two species; O. jipe had a lower mean SGR (1.45 ± 0.14 g/fish⁻¹ day⁻¹) in comparison with (2.28 ± 0.26 g fish⁻¹ day⁻¹) O. 3 niloticus. The DWG also showed the same trend in both species. The DWG for O. niloticus (0.32 ± 0.17 g fish⁻¹ day⁻¹) was significantly higher (t = 4.62, p < 0.05), than that of O. jipe (0.1128 ± 0.01 g fish⁻¹ day⁻¹). The %weight gain (WG) of O. jipe (1.58 ± 0.35 g fish-1) was significantly lower, (t = 3.57, P < 0.05) compared to the mean weight gain of O. niloticus (4.48 ± 1.6 g fish⁻¹).

Figure 3.

Weight gain in cultured Oreochromis jipe and Oreochromis niloticus.

3.1.3 Production parameters

The mean fish yield of O. jipe species was significantly lower (t = 4.46, p < 0.05) in O. jipe compared to the O. niloticus species. The yield in O. jipe ranged between 0.79 and 0.99 kg m⁻³, while in O. niloticus it ranged between 2.79 and 3.15 kg m⁻³. Also, there was a significant difference (t = 2.5, p < 0.05) in FCR between O. jipe and O. niloticus species. The mean FCR varied between 2.35 and 2.57, whereas in O. niloticus it ranged between 1.21 and 1.68 during the culture period. Furthermore, the reciprocal of FCR (FCR⁻¹) yielded food conversion efficiencies (FCEs) for O. niloticus, which were significantly higher than those of O. jipe species.

3.1.4 Water quality parameters

The mean values and variation of water quality parameters recorded during the study are shown in Table 2.

	O. niloticus		O. jipe			Unpaired t-test
Parameter	Mean (± S.E)	Range	Mean (± S.E)	Range	N
Temp.	22.54 ± 0.39	18.5–24.8	22.93 ± 0.31	20.9–26.5	130	p = 0.089
DO	5.94 ± 0.10	4.99 – 6.94	5.04 ± 0.11	4.54–9.37	130	p < 0.001
pH	7.54 ± 0.09	6.88–8.69	8.01 ± 0.13	6.54–9.37	130	p = 0.004
TDS	41.39 ± 3.51	31.6–57.5	40.42 ± 3.53	32.4–56.8	130	p = 0.143
Salinity	0.03 ± 0.003	0.02–0.04	0.03 ± 0.003	0.02–0.04	130	p = 0.173
EC	57.92 ± 4.61	39.7–92.5	57.2 ± 4.55	31.6–89.9	130	p = 0.520

Table 2.

Mean (± S.E) of water quality parameters recorded for Oreochromis niloticus and Oreochromis jipe treatments.

Water temperature showed no significant difference (t = 0.14, p > 0.05) between O. jipe treatment and the control during the culture period. The highest mean temperature recorded was 24.3 ± 0.58°C in the O. jipe culture system, while the temperature in O. niloticus treatment ranged between 18.5 and 24.8^°C, with a mean of 22.54 ± 0.39^°C. However, the DO level was significantly higher (t₁₂₉ = 4.31, p < 0.05) in the control, whereas the pH was significantly (t129 = 2.91, p < 0.05) lower in O. jipe treatment than O. niloticus treatment. The water pH of both culture systems ranged between 7.34 ± 0.09 and 8.37 ± 0.14, whereas DO concentrations ranged between 4.9 ± 0.20 mg L⁻¹ and 6.75 ± 0.14 mg L⁻¹. Total dissolved solids (TDS), conductivity, and salinity showed no significant differences (p > 0.05) between the treatment and the control. Specifically, TDS and conductivity increased progressively after replenishing water in the experimental ponds until the water was exchanged again. However, lower values of conductivity, TDS, and salinity were recorded during the study. Low salinity could be a result of dilution during the rains and the frequent replenishment of water.

4. Discussion

The most crucial interpretations of the study findings based on the overall objective are presented.

4.1 Data variation in O. jipe and O. niloticus culture treatments

The overall variation of the data set is greater for both the O. jipe and O. niloticus species was due to the outliers which ranged from 5 to 20 standard deviations above or below the mean of zero determined by the Partial Least Squares (PLS) regression model [16]. These were attributed to a small number of the faster-growing individuals (shooters), which gained weight faster than the rest of the mixed-sex fingerlings, resulting in un-uniform sizes of fish in each treatment group.

4.2 Growth and survival rates

The study used uniformly homogenous fingerlings, which were expected to grow uniformly throughout the culture period. Upon release into the pond, the surviving fingerlings of both species displayed good condition and consumed feed during the 12-hour monitoring period. However, both growth performance and survival rates of O. jipe were significantly lower than those of O. niloticus. This would have been due to the faster adaptability of O. niloticus to the aquaculture environment because of the previously reported good culture attributes [17]. Chenyambuga et al. [18], confirm that O. niloticus quickly adapts to aquaculture conditions in a comparative study in which the exotic Nile tilapia, O. niloticus attained a final mean weight of 67.6 ± 2.4 g and SGR of 2.2 ± 0.14 g fish⁻¹ day⁻¹, outperforming O. jipe with a final mean weight of 16.3 ± 2.0 and SGR of 1.5 g fish⁻¹ day⁻¹ attained within the same culture period of 90 days. This study however reported lower values of final mean weight and SGR in O. jipe, probably due to temperature difference between the two regions. Whereas, [18] recorded a mean temperature of 25.2 ± 2.0°C, the present study recorded a lower mean temperature of 22.93 ± 0.31°C for the O. jipe species. This temperature lies below the range of 20–30°C recommended for optimum growth and survival of most tilapia species [19, 20]. Nevertheless, the findings on survival rates of O. jipe and O. niloticus agree with the study by [18], who reported higher survival rates of 95.8% in O. jipe and 100% survival in O. niloticus, suggesting that both species can have exceptionally high survival rates if properly managed in the culture system. The findings on survival also concur with Hussain et al. [21], who reported 100% survival of O. niloticus in a polyculture experiment. These findings on survival however differ from the results of [22], who reported low survival rates of 25.8% for O. jipe. The low survival rates of O. jipe reported were attributed to decomposing feed remnants (bioflocs) which were not properly managed in the culture system during the culture trials.

The present study used an open pond system that is semi-controlled by natural factors and the siphoning of bioflocs was done before they settled and decomposed at the pond bottom. This high level of management ensures that the initially slow-growing fish attained a steady and exponential increase in total length and bodyweight, which was recorded from the second month onwards. As a result of slow acclimatization to the captive environment, both species exhibited nonoptimal performance [23]. Low DO levels have been reported to cause fish mortalities and other challenges in the aquaculture production system. The amount of dissolved oxygen consumed by the fish depends on fish size, feeding rate, activity level, and water temperature. In this study, the O. jipe species displayed a remarkable reduction in feed intake immediately after the rains, which might have resulted in the observed low DO levels in this culture treatment. The same phenomenon has been reported in other cultured fish, such as Labeo victorianus by [24], in which the accumulation of unconsumed feed remnants resulted in prolonged low DO levels in the culture ponds, which stressed the fish, resulting in decreased growth and survival rates. Several studies have reported a decline in fish weight gain which has been attributed to decreased water temperatures during cold seasons characterized which directly affect feed intake [21, 25]. This might have occurred in the present study where water physicochemical parameters were not controlled although the pH and DO levels were within the recommended range for tilapia growth [26].

4.3 Water quality parameters

4.3.1 Water temperature

The narrow range of water temperature in both O. niloticus and O. jipe species could be due to the time that temperature readings were taken during the morning hours, which was between 9.00 am and 11.00 am daily. The study, however, did not record any lethal temperature values which range between 10–11°C and 37–38°C, respectively [4]. Although the mean temperatures for both treatments were within the optimum range of 20–30°C required for fish growth [4, 5, 27], these temperatures were below the specific optimum range of 25–30°C recommended for Tilapia growth. The low temperatures could be attributed to a high altitude location of the study area with low mean ambient temperatures ranging between 18°C and 26°C. Although water temperature did not show any significant differences between the O. jipe and O. niloticus treatments, it has been reported that water temperatures below the range of 20–22°C contribute to a nearly 30% decline in optimal growth [5]. This could be the reason for the nonoptimal growth performance of O. jipe and O. niloticus in aquaculture. Probably, the novel species O. jipe were more stressed due to slow adaptability to the changing physicochemical parameters than O. niloticus.

4.3.2 Dissolved oxygen (DO) concentration

The reduction of DO levels in the O. jipe culture system was probably due to low acceptance of commercial feeds, which were administered in their daily ration. O. niloticus species on the other hand consumed all the feed provided within a span of 2–3 hours. This necessitated frequent siphoning of feed remnants that settled at the bottom of O. jipe ponds and flushing of the culture systems with clean fresh water from the tanks was done uniformly to all ponds was done every 2 days. Although frequent siphoning was done regularly, the lack of efficient removal of all bioflocs contributed to the deterioration of water quality resulting in significant differences in DO levels between the O. jipe and O. niloticus culture systems. This result on O. jipe DO levels corroborates with the findings of [22] that attributed low to feed remnants that settled at the bottom of the hapa-in-pond culture system. Lower DO levels have been reported to decrease feeding and respiration in most tilapia species and make it difficult for fish to assimilate the consumed feed [5, 28]. In addition, the amount of dissolved oxygen in the raised ponds was insufficient because the small-sized fingerlings tend to consume additional oxygen to meet the demands for their increased metabolic rates, which doubles for every 10 degrees increase in water temperature within the optimum range [29].

4.3.3 pH

The study found that the mean pH (8.01 ± 0.13) of O. jipe treatment was significantly higher than the mean pH (7.54 ± 0.09) of O. niloticus. Probably, unconsumed pellets particularly in O. jipe treatment could have been decomposed under low DO levels to liberate ammonia (NH₃), which accounts for the range of pH values greater than nine. Although ammonia levels were not determined during the study, studies have shown that ammonia is derived from the breakdown of nontoxic ammonium ion (NH4⁺) contained in digestible crude protein and is a component of total nitrogen highly toxic to fish. However, good water management ensured that the pH did not affect the fish growth and survival because it prevented prolonged exposure of fish to toxic un-ionized ammonia concentrations of greater than 0.2 mg L⁻¹, which can depress the appetite of Tilapia fish [5]. This partly explains why the pH was not consistently high during the study but showed fluctuations between high and low values.

5. Conclusions and recommendation

The study findings showed that the investigated water quality parameters affected the growth performance and survival rates of O. jipe and O. niloticus cultured using raised wooden ponds. As a result, both species did not realize their optimal performance in the aquaculture environment because the temperature fell below the range of 25–30°C recommended for tilapia culture. This might have contributed to low food intake by the species, resulting in low DO and high pH levels. Fish growth was however influenced by the interplay of unmonitored physicochemical parameters in an open pond system. However, for the successful introduction of O. jipe species to aquaculture and optimal growth in the aquaculture environment, it is crucial to delineate optimal culture conditions for the species. This can be done by monitoring the effect of water quality parameters on the growth and survival of fish in a controlled fish culture system and monitoring growth for a longer period. The necessity for a repeat of this experiment in a different culture system, such as hatchery tanks or a greenhouse, to determine whether the results obtained can be replicated under different cultural conditions. In addition, water quality can be recorded using automatic sensor detectors, which take the readings over infinitesimal time intervals and the data collected can be modeled using advanced differential models to evaluate several latent variables in the underlying relationships between water quality and growth parameters.

Acknowledgments

The authors wish to acknowledge the African Development Bank for funding this research through an MSc Scholarship awarded to Mr. J. O. Omweno. Thanks to the Kenya Marine and Fisheries Research Institute (KMFRI), and Kegati Aquaculture Center for technical support.

Conflict of interest

The authors declare that they have no competing personal or professional interests. Further, the funding agency did not play any role in the conceptualization, design, and implementation of the study, as well as the decision to publish the results.

Ethics, approval, and compliance statement

The study was conducted by following all the applicable guidelines stipulated by the National Commission for Science, Technology, and Innovation (NACOSTI) regulations (2014) under the research permit no NACOSTI/P/20/3982 and the Kenya Marine and Fisheries Research Institute (KMFRI) set by Cap 250 of the Science and Technology Act (1979), which has since been repealed by the Science, Technology and Innovation Act (Act no. 28, 2013) and Section 56 of the act that mandates KMFRI to research marine and freshwater resources.