NIGERIAN INSTITUTE FOR OCEANOGRAPHY AND MARINE RESEARCH,

VICTORIA ISLAND, P. M. B. 12729, LAGOS.

DEPARTMENT OF FISHERIES, FEDERAL UNIVERSITY OF AGRICULTURE

UMUDIKE, NIGERIA.

Daytime variations in temperature, dissolved oxygen concentration and pH were investigated at 3-hourly intervals from 6a.m. to 6 p.m. January had the lowest temperature values, while at noon; September and January had the lowest air and pond water temperature values respectively.Dissolved oxygen increase from 6a.m., to 6p.m., with peak values during the 3p.m. readings. ANOVA showed no significant difference in p^H values at the various times of the day (p≥ 0.05), while the t-test showed no significant difference in a seasonal p^H values (p ≥0.05).

Key words: Daytime, temperature, D0, p^H, Ponds

The importance of water quality management in fish ponds and enclosures has been demonstrated by Boyd, (1982, Carmelo, 2002, and Hashim et al, 2002). The quality of pond water estimated by temperature, available oxygen, chemical composition and the level of metabolite waste is a paramount feature, which in addition to other factors affects the growth and health of fish. Various studies have been undertaken globally to investigate fish pond water. In India, Bhattacharya et al. (1988) determined diel variations in water quality of a freshwater pond, while in Nigeria Onuoha et al. (1991) studied the effect of organic fertilization of the productivity of fish ponds at ARAC fish farm. Richter et al. (1982) had earlier stated that water temperature partially determined the extent of oogenesis in brood catfish. This was also similar to later report of Nwadukwe and Ayinla (1993).

Most of the catfish culture practices in Nigeria are carried out in earthen ponds, using semi-intensive method. This involves the application of organic manure at various levels in order to boost primary production, thereby increasing fish yield. The present study is aimed at investigating the variations in pond temperature, dissolved oxygen concentration and pH levels at different period of the day in brood African catfish ponds during the rainy and dry seasons.

The study was conducted at the African Regional Aquaculture Centre (ARAC) at Aluu, Port Harcourt,

Nigeria, from January 1995 to September 1997.

Water from the freshwater zone of the New Calabar river (a tidal system) was pumped into the fish ponds that were used for this study.

Two brood fish ponds (0.1 ha each) were fertilized with poultry manure, which was alternated fortnightly with NPK (15-15-15). Both fertilizers were applied in split doses in order to sustain continuous plankton bloom. Each pond was stocked with both sexes of Clarias gariepinus (Burchell) and Heterobranchus longifilis (Val.) brood fish of various sizes. Feeding was carried out two times daily (8a.m and 4p.m), using a locally compounded diet of 35% protein level, at the rate of 3% of total fish biomass per pond.

differences in the values obtained for the separate parameters at the different times of the day. Student’s t-test at P = 0.1; P= 0.01 was also employed to determine any seasonal differences in the mean values of the separate parameters, as well as between air and pond water temperatures.

The results of air and pond water temperatures at different times of the day are shown in Fig.1. January had the lowest monthly mean values at 6a.m., while March had the highest value. When considering air and pond temperatures, student’s t-test showed a slight significant difference at 6a.m (p≤ 0.01) but not at 9a.m. (p≥0.05). At mid-day, September and January had the lowest air and pond temperatures respectively. While the t-test showed no significant difference between air and pond temperature at mid-day and at 3p.m. (p≥0.05), a slight difference was found at 6p.m. (p≤0.01). When the results of the five periods of the day were considered together for the individual months, Duncan’s multiple range test (p≤0.05) showed a significant difference in monthly air temperatures except between July, August and September. A similar finding was obtained for pond water temperature.

 

 

 

 

 

 

 

 

 

 

Fig. 1 Air and Pond Water Temperatures at 3-hourly Intervals in brood-catfish ponds at ARAC

DISSOLVED OXYGEN CONCENTRATION (D0)

Fig.2 shows the pattern of monthly mean D0 variations during the five periods of the day. At 6 p.m. very low D0 values were obtained and these increased progressively until 3p.m. when peak values were recorded. The 6p.m. when peak values were recorded. The 6p.m. readings sometimes showed slight decrease in values, as shown in Fig. 2. ANOVA showed a significant difference in D0 values, when comparing the results obtained at the five different periods of the day (P≤0.05). When considering the D0 values during the two seasons, the t-test also showed a significant difference between the rainy and dry seasons values during each period of the day (P≤0.01) except at 6a.m. (P≥0.05).

The results of monthly mean pH values are shown in Fig.3. Early morning (6a.m) values were the lowest, and these increased with time of the day. The highest pH values were obtained during the 3p.m. and 6p.m. determination. ANOVA showed no significant difference in pH variations, when the results of the five periods of the day were considered (p≥0.05). During the 25-month study period, the dry season months had a higher pH range (6.0-7.5) than the rainy season months. Student’s t-test however showed that seasonal variation in pH values was not significant during this study (p≥0.05).

Air and pond water temperature values were very similar during the study period. However, pond temperature was relatively warmer at 6a.m. because water retained its heat than air during these periods before and after afternoon sunshine. In a study of Kapitai Lake (Bangladesh), Haldar et al, (1992) found a strong, positive correlation between air and water temperature. In the present study, air and water temperature were also positively correlated. Temperature values were higher during the dry season months (November-March), except in January when cool harmattan winds from the north created a low temperature effect. The rainy season was characterized by heavy rainfall, especially between July and September. This period was also marked by cloud cover, resulting in little sunshine and low temperature. This was similar to the condition described by King and Ekeh (1990) for Nworie stream also in South-eastern Nigeria.

The results showed that daily dissolved oxygen concentration had a similar pattern to that of temperature. Extreme values were obtained, with low early morning concentration (Fig.2). These low values were mainly because of nocturnal decrease in oxygen production due to lack of photosynthesis, while respiration continued. In manured ponds in Israel, Schroeder (1975) observed that plankton and fish respiration couple with atmospheric oxygen diffusion mainly depressed dissolved oxygen values at night. During the present study, low dissolved oxygen values did not seem to cause severe problems to brood African catfish that are known to have accessory air-breathing organs. Thornforde and Boyd (1991) applied aeration in catfish ponds to prevent early morning dissolved oxygen concentrations from falling below 2mg/1. Critical dissolved oxygen values are known to differ according to species. The present results showed that oxygen values increased with daylight and sometimes decreased slightly towards 6a.m. This was similar to the observations of Boyd (1982) who stated that dissolved oxygen in ponds was constantly changing, and that afternoon values were higher than those at dawn. In this study, afternoon values were higher during the dry season, especially during periods of sunshine. This was mainly due to algal photosynthesis, and probably explains the positive correlation between D0 and water temperature at 3p.m. The results also showed that early morning (6a.m.) dissolved oxygen concentrations were higher in the rainy season when temperature values were lower. This was similar to the condition reported for Kapitai Lake by Halder et al. (1992) who obtained the highest dissolved oxygen concentration when temperature was lowest (January to February). The solubility of oxygen in water is indirectly related to temperature and this could have been responsible for negative correlation between them. In the present study, no significant correlation was found between water temperature and dissolved oxygen content, probably as a result of both factors highlighted above. A slight significant correlation was only found between D0 and air temperature at 3p.m. as a result of photosynthesis.

pH value was observed to fluctuate around the neutral zone. This could be attributed to both acidifications (decay of organic manure and excess feed) and alkaline treatment during liming. The values obtained were tolerant limit for fish production as also indicated by Boyd (1982). The pH condition of a pond directly affects the level of un-ionized ammonia concentration, which can be toxic to fish at relatively low values. The present results only showed slight pH fluctuations with highest value of less than 8. Relatively low early morning values that were recorded could be attributed to the presence of carbon dioxide that was produced at night as a result of respiratory activities of aquatic pond biota. Jhingram (1983) had earlier reported that the acidity of pond water was highest just before dawn, and that was similar to the condition found during the dry season of the present study. Lower pH effect was not obvious during the rainy season determinations, probably as a result of the diluting effect of rainwater.

We are grateful to the Management of NIOMR/ARAC for providing the funds and facilities for this study. Thanks to the ARAC Hatchery staff and Mr. Paul Mokayi for their technical assistance.