الفهرس | Only 14 pages are availabe for public view |
Abstract This study was conducted during a period of two years (1986 and 1987) in eighteen fresh water ponds in Abbassa Farm belongs to Aquaculture Development Project, Abu-hamad district, Sharkia Governorate. Ten rectangle 7.5 Fed. earthen ponds (350x75 meters) were used for the first year (1986), and other eight ones of the same type were used for the second year (1987). This work was carried out mainly to investigate the effect of mullet stocking rate on growth traits (body weight and body length), fish production, carcass traits and chemical composition of flesh for tilapia, mullet and carp fish under the polyculture system followed in earthen ponds. Species differences in all traits studied were also investigated., In addi tion, specific growth rate as well as all correlations between weights and lengths of the fish at different growth stages from fingerlings (April-May up to harvesting time (November or December) were calculated. Results obtained could be summarized as follows:- Growth Traits Means and coefficients of variability Means of body weight for tilapia fish in 1986 and 1987, respectively, were 24.9 and 20.2 gm for fingerling stage at April and May, 48.6 and 82.2 gm at July, 63.6 and 147 4 gm at August, 180.4 and 200.8 gm at September, 166.4 and 268.7 gm at October and 267.3 and 288.3 gm at November. The corresponding means of mullet body weight in 1986 and 1987, respectively, for the same growth stages in the same order were 36.4 and 12.9 gm, 78.2 and 60.9 gm, 118.0 and 80.8 gm, 141.4 and 146.6 gm, 188.1 and 206.1 gm and 483.7 and 293.8 gm. For carp fish, means of body weight at April-May, July, August, September, October and November of 1986 were 41.8, 155.6, 157.8, 595.5, 689.1 and 1266.8 gm, respectively. The corresponding means estimated in 1987 were 21.7, 160.8, 229.0, 323.4, 362.9 and 516.4 gm. The average body weight at December, the end of the first year of production (1986), for tilapia, mullet and carp was 283.1, 535.8 and 1433.9 gm, respectively. Differences between the averages of body weight at different growth stages were generally in favour of 1987 for tilapia fish but in favour of 1986 for mullet and carp fish. Coefficients of variability in body weights of tilapia species in 1986 were higher than in 1987. The same picture was generally shown by data of carp species. Rates of increase in body weight between the two years were small at first and started in general to be sizable after July for tilapia fish and after August for either mullet or carp fish. Tilapia fish gained an average of 258.2 gm from May to December in 1986 and 268.1 gm from May to November in 1987. The corresponding average gains in the two years, respectively, were 499.4 and 280.9 gm for mullet fish and 1392.1 and 494.7 gm of carp fish. The averages of body length of tilapia fish in 1986 and 1987, respectively, were 7.5 and 8.3 em at April-May, 10.6 and 15.2 em at July, 13.4 and 19.1 em at August, 19.2 and 21.7 em at September, 18.8 and 23.9 em at October and 24.6 and 24.4 em at November. The corresponding averages for mullet body length in 1986 and 1987, respectively, at the same stages were 12.5 and 9.8 em, 16.7 and 17.1 em, 21.4 and 18.7 em, 24.7 and 22.7 em, 25.8 and 24.1 em and 32.7 and 26.1 em. For carp fish, the averages of body length at April-May (fingerlings), July, August, September, October and November 1986 were 10.7, 18.9, 21.5, 29.4, 32.4 and 42.5 em, respectively. The corresponding averages in 1987 were 8.8, 20.4, 22.9, 25.8, 27.5 and 30.8 em in the same order. The average of body length at December in 1986 were 23.9, 33.4 and 44.0 em for tilapia, mullet and carp fish, respectively. Body length of the fish of each of the three species of the study differed with year of production and the differences were generally in favour of the second year (1987) for tilapia fish, and of the first year (1986) for mullet fish. For carp fish, the means were in favour of the first year at August, September, October and November. Coefficients of variability for body length of tilapia and carp fish were higher in 1986 than in 1987 at most growth stages studied, while the reverse was true for mullet fish. The rate of change in body length did not considerably differ between the corresponding stages of the two years of the study. Tilapia gained an average of 16.4 cm in body length from May to December in 1986 and 16.1 cm from May to November in 1987. The corresponding gains in body length in the two years, respectively, were 20.9 and 16.3 cm for mullet and 33.3 and 22.0 cm for carp. The increase in body weight and length was at its highest level for carp fish and at its lowest level for tilapia fish in the two years of production, indicating that fish of carp species grew faster than fish of the other two species. Factors affectinQ Qrowth traits. Body weight and body length of tilapia fish under polyculture system (with mullet and carp) used in this study varied with mullet stocking rate (MSR) in the two years of production (1986 and 1987), the differences in body weight and length due to MSR were significant (P<0.05 or P<O.Ol or P<O.OOl) in most growth stages studied. The same findings were also observed when dealing with either mullet or carp fish. Differences in body weight and length of tilapia fish due to mullet stocking rate were generally in favour of the lowest rate in 1986 and 1987 from September to the end of the year. The same picture was generally shown for body weight of mullet fish, in 1987 and for body weight and length of carp fish in 1986. Differences in body weight and length of tilapia fish grown under polyculture system during either 1986 or 1987 due to the effect of mullet stocking rate tended to be pronounced after three or four months from the time of stocking. Similar observations were detected for mullet and carp fish. Results of body weight and length when data of the three species (tilapia, mullet and carp) were analysed together, showed a general trend indicating the decrease of individual body weight and length of the fish under the polyculture system with the increase of mullet stocking rate. Differences in individual fish weight and length due to differences in mullet stocking rates were generally significant (P<O.05 or P<O.Ol or P<O.OOl) . Least squares means of body weight and body length of either tilapia, mullet or carp fish at different growth stages in each of the two years of the study varied from pond to another within the different mullet stocking rates used in each year and the differences were mostly significant (P<O. 05 or P<O. 01 or. P<O.OOl). The same results were also obtained when analysing the pooled data of the three species together in either 1986 or 1987. Body weight and body length of fish at different growth stages of the study varied with species, the differences were always significant (P<O.05 or P<O.Ol P<O.OOl) in 1986 and 1987. Carp fish was heavier and longer than either tilapia or mullet fish in each of the two years of the study. At the same time, tilapia recorded the lightest body weight at most growth stages in 1986 and intermediate weight between carp and mullet in 1987. Similarly, tilapia recorded the shortest body length while mullet was intermediate between carp and tilapia for the same trait at all growth stages in 1986 and 1987. Specific Growth Rate Allover specific growth rate (SGR) of carp in 1986 and 1987 and of mullet in 1987 was higher than that of tilapia in 1986 and 1987 and that of mullet fish in 1986. The SGR of all species exhibited relatively high values from July till November. However, the highest SGR of tilapia or carp fish was observed in September of 1986 and in July of 1987, while the highest SGR for mullet fish was obtained in November of 1986 and in July of 1987. Correlations Between Growth Traits Coefficients of correlation between body weight and body length of the fish at each stage from July up to the harvest time in the two years were high and tended to increase with advance of growth stage. Correlation coefficients between body length at a particular stage and body length of the successive stages were generally higher than those between body length at that particular stage and body weight of the successive stages of growth. Correlation coefficients between body weight at a certain stage and body weight at the next stage increased as the fish grow older, the same picture could be seen when considering body length. Fish Production Means and coefficients of variability. Production means per pond and per feddan, respectively, for tilapia fish at the harvest time were 1183.2 and 190.7 Kg in 1986 and 615.1 and 59.4 Kg in 1987. The corresponding means were 495.0 and 79.8 Kg in 1986 and 416.9 and 67.1 kg in 1987 for mullet fish while were 1660.7 and 266.7 Kg in 1986 and 1678.9 and 270.1 Kg in 1987 for carp fish. Production of tilapia and mullet fish in the first year (1986) was higher than that in the second year (1987), while production of carp fish did not differ considerably from the first to the second year. Also, the total production of the different fish species was higher in 1986 than in 1987 (3338.9 vs 2710.9 Kg per pond and 537.2 vs 432.6 Kg per feddan). The same picture could be seen when considering the total production of tilapia, mullet carp, carnivorous and skerta (3858.3 vs 3089.0 Kg per pond and 621.9 vs 493.7 Kg per feddan). Coefficients of variability of production per pond or per feddan were shown to be higher in 1986 than in 1987 for mullet, carnivorous and skerta fish, lower in 1986 than in 1987 for tilapia fish and nearly similar in the two years for carp fish. Factors affecting fish production. The highest fish total production was recorded by fish of the lowest mullet stocking rate in the first year (15000 fingerlings/ pond) and by fish of the intermediate mullet stocking rate in the second year (12000 fingerlings/pond). The same picture was opserved when dealing with fish production per feddan. The highest mullet stocking rate was generally associated with the lowest fish production. Mean production per pond or per feddan of tilapia and mullet fish was the highest with the stocking rate of 18000 mullet fingerlings/pond in each of the two years of the study (1986 and 1987). Carp fish production was observed to be the highest with the stocking rate of 15000 mullet fingerlings/pond in 1986 and with that of 8000 mullet fingerlings/ pond in 1987. The increase of carnivorous fish production was associated with decrease in either mullet or carp production while tilapia and skerta increased. On the other hand, the increase in carp production caused a decrease in mullet and tilapia production in both of the two years of the study. However, statistical analysis of the effect of MSR on total production, and the production of each of fish species studied either per pond or per feddan in the two years were non-significant. Carcass Traits Means of carcass traits of fish in 1986 were mostly higher than their correspondings in 1987. Carcass traits studied varied with species of the study, the differences were mostly significant (P<O.05 or P<O.Ol or P<O.OOl) in 1986 and 1987. Means of weights of whole fish, flesh, head, skeleton and viscera, in general, were the highest for carp followed in decreasing order by mullet and tilapia in 1986. In 1987, this ranking was reversed, the highest weight of these traits were recorded by tilapia followed in a decreasing order by mullet and carp. Means of the flesh percentage and other carcass traits (as percentages) in the three species in any of the two years of the study followed the same ranking for the whole fish weight. Mullet stocking rate affected most carcass traits studied significantly (P<O.05 or P<O.Ol) but without any consistent trend in the two years. Differences between ponds within mullet stocking rate in carcass traits were mostly non-significant in the two years. Effects of the interactions between mullet stocking rate and species were significant (P<O.05 or P<O.Ol or P<O.OOl) on all carcass traits in 1986 and 1987 1987 only. except by-product pre cent in Chemical composition of fish flesh. Average moisture content of fish flesh was found to be the highest for tilapia fish followed by carp then mullet fish in a decreasing order in either 1986 or 1957. Spec es differences in moisture content were significant (P<O.OOl) in the two years of the study. Mullet fish recorded the highest dry matter content then followed in a decreasing order by carp and tilapia. Differences in dry matter content due to species effects proved significant (P<O.OOl) in both of the two years of the study. Protein and fat contents of fish flesh were the highest for mullet with significant discrepancies from either tilapia or carp in 1986. The same picture was shown for fat content only in 1987. Species differences for protein and fat percent in the fish flesh were mostly significant (P<O.05 or P<O.OOl) in the two years of the study. Fish flesh content from ash in tilapia was found to be significantly (P<O.05) lower than in either mullet or carp fish in 1986 and 1987. The effect of mullet stocking rate was significant (P<O.OOl) for fat and ash percentages and non-significant for moisture, dry matter and protein contents in 1986, for 1987, the same effect was non-significant on all contents. ConstitUents of fresh fish flesh of the three species studied (moisture, dry matter, protein, fat and ash) differ between ponds within mullet stocking rate, but without significant differences in most cases The effect of interaction between species and mullet stocking rate were not significant (P>O.05) on moisture, dry matter and protein percentages in 1986 while was significant (P<O.05 or P<O.OOl) on fat and ash percentages. In 1987, effect of this interaction was found to be significant (P<O.05 or P<O.OOl) on components of chemical composition except protein and ash. |