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The potency of crude pituitary extract from Roundup -exposed homoplastic donors in induced breeding of Clarias gariepinus was studied. Crude pituitary extract from fish exposed to 6mg/L of the toxicant for ten weeks were used to induce oocyte maturation, ovulation and spawning in the female fish. Results showed that there were no significant differences between latency period, fecundity, gonadosomatic index, undeveloped and hatched eggs; normal and deformed fry and percent fry survival of the control and the treatment (P>0.05). However, the values of these parameters were consistently higher in the control than in the treatment. But the percent fertilization and number of fertilised eggs in the treatment were significantly higher than that in the control(P>0.05). Observations from this seem to suggest that although induction of oocyte maturation, ovulation, spawning and survival of fry may not be negatively influenced by the use crude pituitary extract of exposed fish, however, such fry may have poor conversion ratio and hence poor growth performance.
Crude pituitary extract , Clarias gariepinus, Homoplastic donors
Artificial propagationis the most effcient means of meeting the ever-increasing demand for fish seeding and several natural and synthetic hormonal preparations have been successfully used in artificial propagation od several culturable species including the clariids (Hogendoorn and Visman, 1980 and Nwadukwe, 1992). However, it appears that the most commonly used technique in selctive hybridisation is hypophization rather than induction with synthetic hormones because of the fish pituitary was the site of gonadotropic hormonal activities.
Hormones are biologically active molecules that control growth, behaviours, development and reproduction, thus are crucial to many life functions (USEPA, 2000). However, levels of several of these hormones have been affected by environmental contaminants resulting in the disruption of reproductive processes in fish (Cooper, 1999 and Schultz, et al. 1995). Levels of both male and female hormones smong several others have been disupted by a number of herbicides (Saxena and Mani, 1985 and Cox, 2001, 20001a). A study of eleven river showed a striking relationship betwen pesticide contaminations of river water and the ratio of the ‘female’ and ‘male’ sex hormones in fish. In female fish, level of female hormones is normally four times higher than that of male hormone, but this ratio declined at higher pesticides concentrations. Pesticides caused a 15-delay in adult spawning and reduced the number of larve and growth of young-of-the year in bluegill goldfish(Tanner and Knuth 1996 and Moore and Lower 2001). Singh and Singh (1992) showed that exposure of female Heteropneutes fossils to 20 μg/L malathion and 16mg/L gamma-BHC for four weeks during phases of reproductive cycle hampered sex steroid metabolism disturbing steroid regulation resulting in hormonal imbalance. Sublethal levels of PCB and mirex according to juvenile rainbow trout induced with 17β-estradiol. Atrazine at a concentration of 0.04ppb reduced the release of a sex hormone from the tests cells in the Atlantic salmon resulting in a 50% decrease in milt production (Moore and Waring 1985). It distrupted gonadotropic mechanism in rat (Kniewald et al. 1987).
Glyphosate has been extensively used for aquatic weed control in Nigerian water bodies (Olaleye and Akinyemiju 1993; 1995; 2002). But the recommended maximum concentration in one meter water column after application is 0.6mg/L (Price 1976) which may be exceeded during field applications as the authority concern do not monitor this. The influence of herbicides like glyphosate on the reproductive process of exposed fish particularly Clarias grriepinus has been reported. The study was conducted to asssess the efficacy of pituitary from C.grriepinus exposed to Roundup, (glphosate) in inducing ovulation and spawning in the female fish.
Sixteen adult C. gariepinus (mean weight, 483.34+153g, sem) used in this study were obtained from a private farm and transported to the laboratory, Department of fishries, Rivers University of Science and technology, Port Harcourt at different times. Four fish were exposed individually to 40L 6ppm Roundup in 70L plastic circular aquaria for 10 weeks.. The fish was fed a 35% crude protein diet at 1% biomass twice daily at 9000 and 1600hours. A quarter, half of the solution was renewed every 24 and 48 hours, respectively. Complete exchange was done every 72 hours. Eight gravid females, two ripe male and three other fish were obtained for spawning from the same source three days to the end of the exposure period. These were held under similar conditions as above.
Pituitary glands were colled from the exposed and unexposed fish, respectively and preserved in acetone (Viveen et al. 1986). Injection of female spawners, collection of milk from the ripe males, stripping of eggs and fertilization were done as suggested by the above authors. Fertilized eggs from each fish were incubated on ‘kakaban; in hatchery trays (inner diameter, 41x31x26cm3) held in incubation tanks filled to two-third volume. The tanks were gently aerated and dissolved oxygen,pH and temperature were read daily. Some three hours after fertilization, unfertilized eggs, which appeared whitish were siphoned out. At about 10 hours from the start of incubation, the volume of air from the aerators was adjusted to sixth day. Thereafter the fry were fed ad libitum on a 50% crude protein diet composed of groundnut cake, shrimp and fishmeal until the 14th day.
The number of eggs stripped the gonadosomatic index (GSI), latency period, relative percentage of eggs to body weight, percentage fertilization, hatchability, survival and number of hatchling were determined based on the work of Viveen et al. (2001) were used to assess growth performance of the fry. Data for the various parameters were subjected to t-test, p>0.05 (Wahua, 1998).
There were no significant differences between all the parameters studied between the control and treatment (p>0.05, Table 1 and 2) except in the number of eggs (fecundity). However, the values of these parameters were consistently higher in the control than in the treatment growth performance of the fry showed that fry from the control group had better food conversion ratio, specific growth rate and weight gain, although these were not significantly different (p>0.05, Table 3).
The study revealed there was no significant difference in the pituitary from C.gariepinus exposed to glyphosate and the control including oocyte maturation, ovulation and spawning in the fish. the latency period (9-10 hrs) obtained from this study agrees with that reported by Ayinla and Nwadukwe (1998), but it is three hours longer than that reported by (Viveen et al. 1986). Woynarovitch and Hovath (1980) and Borode (1998) stated that some environmental factors such as temperature, pH dissolved oxygen, calmness were believed to play important roles in ovulation and that temperature is of vital importance. The highest relative percentage of eggs to fish body weight (15%) was recorded for the smallest female fish of 300g in the control followed by the 400g (10%) in the treatment. Such inconsistency has been reported by other workers (ayinla and Nwadukwe, 1988 and Ugwumba and Ugwumba, 1995). Madu et al. (1999) maintained that there was no correlation between the weight of female brood fish and the weight of the eggs released. According to these authors, what matters is the maturity of the brood fish, readiness of the eggs, effectiveness of the hormone used and some environmental factors.
This work showed that the treatment did not produce any significant difference in the fecundity and GSI of the fish. The number of eggs stripped from brood fish could not be based on the effectiveness of each hormonal treatment alone as other factors have been shown to affect fecundity of brood fish. Although the effectiveness and potency of the hormones used matter, yet maturation, ovulation and the final spawning (stripping) of the eggs are influenced by season, size of brood fish quality of feed fed to brood stock (Nwadukwe and Ayinla, 1993). the smallest female brood fish (300g) was the most sensitive to the hormonal treatment with a GSI of 17.6% (Table 1) confirming the finding of Ugwumba and Ugwumba (1995) that highest sensitivity to hormonal treatment was recorded in the smaller C.gariepinus that gave the highest percentage weight of eggs.
Percent fertilization of 91.3% for the treatment and control respectively was good and compares favourably with published results for C.gariepinus under similar conditions (Nwadukwe, 1990). The incubation time of 24-36 hours in this study was higher than that recorded by Viveen et al. (1998) and Borode (1998) for C.gariepinus, reciprocal F1 between C.gariepinus and Hereobranchus bidorsalis their parental crosses. The incubation tank temperature has been identified by Borode (1998) as being responsible for these differences. The fry aborbed their yolk sacs within four days the range of time suggested by Viveen et al. (1986) for C.gariepinus. The average percentage hatchability or larval production (treatment, 68.5%, control 71.3%) out of which up to 68.7% and 72.4% respectively survived showed an overall good egg quality and effectiveness of the crude pituitary from both the treatment and control in inducing ovulation and spawning in the African catfish. The values are similar to those reported by (Ugwumba and Ugwumba (1995) for the same species. However, these are higher than those reported by other worker for the same species or their hybrids. Nwadukwe and Ayinla (1988), Nwadukwe (1995) and Aluko et al. (2000) recorded 54-74% hatching sucess for C.gariepinus, H.longifilis and their reciprocal F1 hybrids in aerated fiberglass and glass aquaria. Hatchability of eggs from C.gariepinus and H. bidorsalis hybrids and their parent crosses incubated in glas tanks with water flow-through aeration was between 29.5-35.8%. Also in crosses between males F1 hybrid broodfish and males F1 hybrid, C.gariepinus, H.longifilis to produce F2 and back cross generation the values between 13-26%.
Fry from the control performed better than those from the treatment (Table 3) however, the weight gained by both was higher than those reported by Viveen et al.(1986) and de Graaf and Janssen (1996). This notwithstanding, the results seeem to suggest that induction of oocte maturation, ovulation and spawning of C.gariepinus with pituitary from glyphosate-exposed fish may have impacted negatively on the performance of the fry.