Zosipat M. Beniga and Antonio V. Circa

GROWTH PERFORMANCE EVALUATION OF GENETICALLY IMPROVED NILE TILAPIA (OREOCHROMIS NILOTICUS L.) IN FLOATING CAGES IN LAKE SEBU, SOUTH COTABATO, PHILIPPINES

Zosipat M. Beniga and Antonio V. Circa

Freshwater Aquaculture Center, Central Luzon State University

Muñoz, Nueva Ecija, Philippines

Abstract

The study evaluated the growth performance of genetically improved O. niloticus in floating cages in Lake Sebu, South Cotabato. The genetically improved Nile tilapia tested were: Genetically Improved Farmed Tilapia (GIFT), Genetically Male Tilapia (GMT), and Selected Line. Locally produced commercial strain served as the Control. GIFT fish was developed through a breeding program that combines selection of diverse genetic groups of O. niloticus. GMT is a product of “YY-male” technology that involves chromosome manipulation. Selected Line is a product of a within family selection program.

Floating net cages (2m x 2m x 2.5m) were used as culture facilities. The test fish were randomly stocked in each cage at 30 pcs/m2 fed with commercial tilapia diet with 30% crude protein diet in an 84-day growing period. Results revealed that Selected Line had the highest mean final weight (82.0g) with a corresponding mean growth rate of 0.94g/day. Following Selected Line were GMT, GIFT and the Local strain with mean body weights of 69.3, 67.3 and 58.1g; and daily growth rates of 0.78, 0.76 and 0.65g, respectively. ANOVA showed that Selected Line had grown significantly better than the other genetically improved tilapia (P<0.05). GIFT and GMT had no significant difference in growth rates. On survival, GMT obtained the highest with 96.6% followed by GIFT with 94.2%. Selected Line had the lowest survival rate of 85.3%. Water quality parameters were observed to be within the optimum range for culture of tilapia. Cost and return analysis proved that all genetically improved fish were more profitable to grow than the Local strain in Lake Sebu.

INTRODUCTION

Global tilapia production has reached more than 500,000 MT (Popma and Lovshin, 1996). Tilapias, the word used for a group of cichlid fishes, although native to Africa is now farmed worldwide and its products become widely-traded commodities (Pullin, et al., 1984). Hailed as “potentially an international food commodity” (Pullin, et al., 1984)., dubbed as an “aquatic chicken” (Maclean, 1984), “everyman’s fish” (Pullin, 1985), and most recently “trendy” (Emerson, 1994 as cited by Pullin, et al., 1984). Tilapia is now gaining wide acceptance as table food both in the local and international market. The rising popularity of tilapia for cultivation is attributed to the introduction of Nile tilapia (Oreochromis niloticus). This species has the characteristics of fast growth, high resistance to parasites and diseases, tolerance to poor water quality and ability to survive in a wide range of environmental condition (PCAMRD, 1994; Guerrero, 1985).

Guerrero, (1995) reported that in 1993, the Philippines produced 93,339 metric tons of tilapia in aquaculture, and tilapia fingerlings estimated to be about 600 million annually making it one of the world’s largest grower. Of this volume, freshwater ponds contributed 37% of the total tilapia production (BFAR, 1994). However, in spite of this development the tilapia industry of the country is confronted with a very serious problem. Poor quality of fingerlings used in production systems has become a constraint to the further expansion of the industry. Unconscious husbandry practices, introgression of feral Oreochromis niloticus, founder and bottle neck effects, and inbreeeding as a consequence of poor stock management may have caused genetic deterioration resulting in reduced performance of farm tilapias (Abella, et al., 1986; Macaranas, et.al., 1986; Pullin and Capili, 1988; Guerrero, 1994). This problem has become so alarming that some government research institutions were prompted, in collaboration with international research organizations, to start the work on the genetic improvement of tilapia.

Researches on tilapia genetic improvement are now currently done at the Freshwater Aquaculture Center of the Central Luzon State University (FAC/CLSU) and the National Freshwater Fisheries Training Research Center of the Bureau of Fisheries and Aquatic Resources (NFFTRC/BFAR), also in Muñoz, Nueva Ecija. The Genetic Improvement of Farmed Tilapia (GIFT) Project implemented by the International Center for Living Aquatic Resource Management (ICLARM) in collaboration with FAC/CLSU and NFFTRC/BFAR and supported by international funding institutions such as Asian Development Bank (ADB) and the United Nations Development Program (UNDP) has successfully developed an improved and fast-growing breed of Nile tilapia through selective breeding. This synthetic strain is popular by its acronym as GIFT (Genetic Improvement of Farmed Tilapia).

The International Development Research Center (IDRC) fish Genetic Project, also at FAC/CLSU, has achieved significant results in testing within-family selection as a procedure for improving the growth of O. niloticus. The project has produced a fast-growing breed of tilapia known as Selected Line. On the other hand, the Genetic Manipulation for Improved Tilapia (GMIT) Project is being conducted at FAC/CLSU in collaboration with the University of Wales in Swansea. The project has developed a novel YY-male genotype that when mated with normal XX-female generates all-male progenies dubbed as Genetically Male Tilapia (GMT). Except for the within-family selection, the other genetic improvement projects have for some years been distributing quality fingerlings throughout the Philippines for commercial use. The Selected Line has never been commercialized.

Prior to distribution for commercial production purposes, the growth performance of GIFT and GMT was evaluated along with the domesticated or Local Strain in different on-station and on-farm trials. Results of different studies showed that the improved tilapia performed significantly better than their respective counterpart, the Local Strain. The GIFT fish for example, had shown 60% faster growth rate and 5% better survival than the domesticated strains (Eknath, 1992; ICLARM, 1993). Likewise, Genetically Male Tilapia (GMT) was also found to perform better than the mixed-sex tilapia (MST) and sex-reversed tilapia (SRT) as reported by Mair et.al. (1994; 1995). Similarly, the Selected Line, a product of within-family selection has also grown significantly faster than the control line (Bolivar, et al., 1992; Bartolome, et al., 1994).

Cage culture has been the major activity of the people in the Lake Sebu for the past two decades (Dongon, 1994). The tilapia industry is considered the backbone of the economy of the municipality (Loco, 1994). However, the present production systems require more feed inputs and longer growing period. Physical deformities or abnormalities of the tilapia stocks used at present are now prevalent. The declining fish production and the prevalence of deformities on the fish could be attributed to deteriorating quality and perhaps a high degree of inbreeding. The development of genetically improved tilapia is hoped to bolster again the tilapia production in this lake. But the question on which of them is best suited to this particular culture environment remains to be seen. Hence this study was conceived.

MATERIALS AND METHODS

This study used twelve floating net cages (2m x 2m x 2.5m). Big bamboo poles were used as flotation materials. A Local strain and three genetically improved O. niloticus were grown and tested for their culture performance from October 1995 to January 1996 in Lake Sebu, South Cotabato, Mindanao. Lake Sebu, which lies in the rugged highlands of South Cotabato has a total water area of 354 hectares (Figures 1). It has an elevation of about 700 meters above sea level and with a maximum depth of 45 meters. The lake water temperature ranges from 27 to 280C (Gracia et al., 1984).

The experiment followed the Randomized Complete Block Design (Gomez and Gomez, 1984). The study was originally designed for 120 days, but was terminated earlier due to the occurrence of mass fish kill, (locally known as “kamahong”) on the 96th day of culture. This study considered the data from the last sampling period (84th day) as harvest data. A complete fish inventory during each sampling period exists but sex ratios were not determined during these periods as too much handling is stressful to the experimental fish. The test fish are as follows:

Local Strain

The Local strain or commercial strain Nile tilapia was acquired from one of the local hatcheries in South Cotabato.

Selected line

The selected line O. niloticus was the 13th generation of within-family selection for growth. Abella et al. (1990) described the details of the selection procedure. Breeders were obtained from the IDRC Fish Genetic project at the Freshwater Aquaculture Center, Central Luzon State University (FAC/CLSU), Muñoz, Nueva Ecija.

GIFT Fish

Third generation fingerlings of the Genetically Improved Farmed Tilapia (GIFT) were obtained from NFFTRC/BFAR, CLSU, Muñoz, Nueva Ecija. GIFT fish was developed through a breeding program that combines selection of diverse genetic groups of O. niloticus by ICLARM (International Living Aquatic Resources Management) and its collaborating research institutions.

GMT Fish

The Genetically Male Tilapia (GMT) fingerlings of about size #24 were obtained from the Genetic Manipulation for Improved Tilapia (GMIT) project at FAC/CLSU. GMT is a product of “YY-male” technology that involves chromosome manipulation developed by University College of Swansea, UK.

Fish stocking and stock sampling

All the test fish were reared in separate net cages in the experimental site for about a month to condition them to the environment and to feeding of commercial diet. During stocking, the mean weight of fish ranged from 3.2 to 3.5 g across treatments. Each cage was stocked with 120 individuals (30 individuals/m2), about 10% of which was taken at random for initial weight and length measurements. Subsequent samplings (15% of the stocks) were done every three weeks thereafter. Total stock inventory by head counting of the surviving fish was done during sampling. This was done in order to have an accurate estimate of fish survival and therefore feed ration. Recording of dead fish was done daily.

Feeds and Feeding

The test fish were fed with commercial tilapia feed following the recommendation of Guerrero (1980). The daily feed ration was given in three equal parts at 7:00-8:00 AM, 11:00-12:00 NN and 4:00-5:00 PM. Feeding was done by simply broadcasting the feed into the water, seven days a week except during sampling. Feed ration was computed as the product of fish biomass and feeding rate. Adjustment of feed ration was effected after every sampling.

Water Quality Monitoring

Selected water quality parameters such as dissolved oxygen (DO), temperature (0C), hydrogen ion concentration (pH) and secchi disc visibility (SDV) were monitored once in two weeks. Dissolved oxygen was monitored using YSI 51B D.O. meter and a Checkmate 90 Corning D.O. meter. Water temperature was measured using the built-in thermometer in the YSI 51B D.O. meter and further checked with a mercury thermometer. Lab type and pen type HANNA pH meters were used in monitoring water pH. A wooden secchi disc measured the water visibility or transparency. Water samples were taken from inside each cage, one replicate per treatment. Another sample was taken from outside of the cages. Aside from the regular schedule, dissolved oxygen and water temperature were also monitored on a 24-hr period at 2-hr interval on a monthly basis.

Economic analysis

Cost and return analysis was done to compare the profitability of producing fish using the genetically improved and Local strain Nile tilapia. Only cash cost and returns were considered in the analysis.

Statistical Analysis

Data on growth, percentage survival, food conversion ratio, and fish yield were subjected to analysis of variance (ANOVA) using IRRISTAT Software. Duncan’s Multiple Range Test (DMRT) was used in the comparison of treatment means. The interrelationships between the fish and water quality variables were examined using correlation analysis.

RESULTS AND DISCUSSION

Growth and survival

Figure 1 illustrates the growth trend of the test fish. Growth rates increased as the culture period progressed. At Day 21, while growth rate across treatments was still very minimal, Selected Line had already shown better performance over the others.

At Day 84, Selected Line had the highest mean final weight of 82.0g. with a corresponding mean daily growth rate of 0.94g. Following Selected Line was GMT with a final weight of 69.3g and a growth increment of 0.78g/day. GIFT followed closely with GMT with a mean final weight 67.3g and a daily growth rate of 0.76g. The Local Strain gave the lowest growth performance, with a mean final weight of 58.1g or a daily weight gain of 0.65g. ANOVA revealed that the Selected Line had significantly higher growth rate than the other test fish; GIFT and GMT had comparable growth rates (P<0.05).

Survival

ANOVA revealed that GMT and GIFT had comparable survival rates. However, their survival rates were significantly higher than both the Selected Line and Local strain (P<0.05). Across treatments survival ranged from 85.3 to 99.6% with GMT obtaining the highest followed by GIFT and the Local Strain with 94.2 and 86.6%, respectively. Selected Line showed comparable survival rates with the Local strain but significantly lower compared to the other improved fish. The low survival rate of the Selected Line during the later periods was due to mortality caused by fungal infestation. During this period, fungal infestation was observed everywhere in Lake Sebu. The test fish were believed to have been subjected to the same kind of stress and infectious agents but only Selected Line was adversely affected. It could be deduced that Selected Line is less disease-resistant than the other improved fish. Susceptibility and resistance to disease could be attributed to genetic differences.

The low survival rate of Selected Line may have been the reason for having a higher growth rate. However, the data show that it was only in the last three weeks that survival rate of Selected Line became significantly lower compared to GIFT and GMT, but starting from Day21 to Day 42 the survival rate of Selected Line was comparable with GIFT and GMT. During these early periods, Selected Line had already shown significant difference in growth rate over the other test fish.

The mass fish mortality that took place on the 96th day of culture was believed to be caused by dissolved oxygen depletion. Data on a 24-hour monitoring indicated a very low dissolved oxygen, as low as 0.1mg/1 on the day prior and during fish kill. This condition has been aggravated by the prolonged bad weather condition in the place caused by the occurrence of a typhoon.

Fish Production

Table 1 shows the summary of fish production. Production in a 4-m2 cage was 6.0, 8.4, 7.6 and 8.0 kg for the Local strain, Selected Line, GIFT and GMT, respectively. Highest production was obtained in Selected Line followed by GMT, GIFT and Local strain.
ANOVA showed that Selected Line produced comparatively with GMT but significantly higher than GIFT and Local strain. On the other hand, GMT and GIFT showed no statistical difference in production. Fish production of Selected Line did not differ significantly GMT in spite of the latter’s high growth rate because of its low survival rate. The computed differences in yields of the improved tilapia over the Local strain were 40.0, 26.6 and 33.3% better for Selected Line, GIFT and GMT fish, respectively. On the average, genetically improved tilapia was 33.3% better in yield compared to commercial strain. Overall, fish yield was quite good considering the size of the fish at stocking and the shorter growing period.

Cost and Return Analysis

Results showed that GMT had the lowest production cost of P18.50/kg of fish and the highest rate of return of 35.1%. In contrast, the Local strain had the highest cost of production and the lowest rate of return of P22.96/kg of fish and 8.8%, respectively. GMT had higher net return compared to Selected Line despite the higher growth rate of the latter because of the former’s high percentage survival and a slightly higher food conversion ratio. The use of the “new strains” was found to be more profitable than the Local stocks of Nile tilapia in Lake Sebu. The Selected Line showed higher fish production but GMT had shown higher profitability.

Table 1. Fish production summary of genetically improved and local strains of Oreochromis niloticus in 4m2 floating net cages after 84 days of culture. Means within each column with different letter superscripts are significantly different (DMRT, P<0.05). Numbers below each mean with ± are standard deviations.

Strain
Treatment / Initial Body Weight / Final Body Weight / Daily
Weight Gain / Survival
Rate / Yield / Production Cost / Rate of Return
(g/fish) / (g/fish) / (g/fish) / (%) / (kg/4m2) / (P/kg) / (%)
Local Strain / 3.5 a / 58.1c / 0.65 C / 86.6 bc / 6.0 b / 22.96 / 8.8
±0.4 / ±1.6 / ±0.2 / ±1.4 / ±0.6
Selected Line / 3.2 a / 82.0a / 0.94 a / 85.3 c / 8.4 a / 19.50 / 28.1
±0.9 / ±1.8 / ±0.2 / ±2.7 / ±0.9
GIFT / 3.3 a / 67.31b / 0.76 b / 94.2 ab / 7.6 a / 20.05 / 24.5
±0.6 / ±2.2 / ±0.2 / ±1.2 / ±0.7
GMIT / 3.4 a / 69.3b / 0.78 b / 96.6 a / 8.0 a / 18.50 / 35.1
±0.6 / ±1.8 / ±0.2 / ±1.1 / ±0.6

Water Quality Parameters