Relationships among Gonad Weight , Liver Weight and Body Weight of Major , Common and Some Chinese Carps under Composite Culture System with Special Reference to Pond Fertilization

The relationship of gonad weight and liver weight with body weight of six fish species viz; Catla catla, Labeo rohita, Cirrhina mrigala, Hypophthlamichthys molitrix, Ctenopharyngodon idella and Cyprinus carpio under the influence of artificial feed, broiler manure, buffalo manure, N:P:K (25:25:0) and a control pond were examined after a rearing period of one year. The positive relationship between gonad weight and body weight was significant which showed the dependence of gonadal development on body weight in all the six fish species. The currelation coefficients were higher in female fishes. However, the major carps had a much smaller proportional gonadal weight as compared with Chinese carps and a common carp due to their faster growth rate. The overall comparison of six fish species under different experimental treatments revealed that highest liver weight was observed for C. idella closely followed by C. carpio. The maximum correlation value was observed with H. molitrix under the broiler manure. The maximum Gonadosomatic Index (GSI) remained as 32.63 for C. carpio followed by C. idella. The maximum value for Hepatosomatic Index (HSI). remained 1.99 for C. idella followed by C. mrigala. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 5 : 740-744)


INTRODUCTION
The condition of fish is affected by its gonad weight and visceral weight.However, in some fish species the gonad increases isometrically with body weight (LeCren, 1951).Dunham et al. (1985) mentioned that viscera percentage had phenotypic association with dressing percentage.They found that no traits could be measured from live fish that would predict viscera percentage.In most teleostean species gonadal weight depends, in part, on body weight (Mahboob and Sheri, 1997).One of the most common ways to account for the effect of body size on gonadal size has been to represent gonadal weight as a percentage of body weight, and the gonadosomatic index (GSI) introduced by Mein (1927) has often been used as an indicator of relative gonadal development or activity.GSI presumes a constant arithmetic relationship of gonadal weight over the range of fish weight being sampled.
Gonadal recrudescence in female fish involves an accumulation of lipid and protein stores within the developing oocytes (Mahboob et al., 1990).These stores may come from liver and may be inversely correlated with oocyte development in some species.Liver size in a given sample of fish is correlated with body weight minus liver weight and expressed as Hepatosomatic Index (HSI).This expression makes the same assumption as with GSI.Delahunty and DeVlaming (1980) reported ovary weight significantly increased relative to increasing body weight in the gold fish, Carassius auratus.The exact nature of this relationship changed from month to month.They further pointed out that larger fish were found to have proportionately larger ovaries than small fish at specific times of the year.The relationship of liver weight to body weight varies seasonally.Eliassen and Vahl (1982) reported that in mature cod the gonad was found to increase isometrically with fish weight suggesting that the relative energy demand for gonadal growth is independent of fish size.
The primary objective of this study was to establish relationships among gonad weight, liver weight and body weight and their meat bone ratios as influenced by fertilizers and artificial feed in composite culture of major, common and some Chinese carps.

MATERIALS AND METHODS
The experiment was started on November 30, 1997 under ambient conditions typical of Faisalabad and completed on November 25, 1998.Ground water of Faisalabad is somewhat salty.Fifteen newly dug earthen fish ponds of dimensions 15 m×8 m×2.5 m (length×width× depth) were used in three replicates in a factorial design for this experiment.Approximately four months old fingerlings of Catla catla, Labeo rohita, Cirrhina mrigala, silver carp (Hypophthalmichthys molitrix), grass carp (Ctenopharyngodon idella) and Cyprinus carpio were stocked in each of the ponds with the stocking density of 2.87 m 3 /fish (Javed, 1988).The interspecies ratios were adopted according to Lakshmanan et al. (1971) (table 1).The percentage N, P and K in the four treatments materials in this study were obtained by A.O.A.C. (1984) methods as shown in table 2.
Feed supplementation of T 1 and fertilization of T 2 , T 3 and T 4 was done with broiler manure, buffalo manure and N:P:K (25:25:0) based on their nitrogen contents at the rate of 0.15 gm nitrogen per 100 gm of wet fish weight daily for one year.However, control pond (T 5 ) remained without any additives.

Physical analysis of fish meat
At the end of trial period on November 26, 1998 the seven fish of each species were randomly selected and were dressed and used for the analysis of meat/bone ratio.The big bones were separated by hand while the small bones were separated by suspending fish meat in a solution of 0.01 percent KOH with gentle heating (Javed, 1988).Precautionary measures were exercised to prevent the erosion of bones by successive bathing in distilled water; the moisture was allowed to absorb on blotting paper and weighed to obtain a final value for bones in fish.

Study of fish viscera
Fish viscera were analyzed at the end of experimental period for weight and the size of gonad and liver to study their possible relationship with fish weight.Seven fish of each species from each of the pond were randomly selected and killed the day after being received, which allowed 24 h starvation period.Correlation analysis among gonad weight, liver weight and body weight was worked out using the MSTAT package.

Dressing losses and meat/bone ratios
The percentages losses in dressing and the meat/bone ratios are presented in table 3.In Catla catla the losses during dressing of fish were 29.23, 24.63, 32.02, 26.91 and  34.09 percent from T 1 , T 2 , T 3 , T 4 and T 5 , respectively.L. rohita showed the minimum and maximum losses as 21.25 and 32.36 under the effect of T 5 and T 4 , respectively (table 3).In C. mrigala the dressing percentage losses were 26.98, 22.30, 30.75, 25.34 and 34.47 for T 1 , T 2 , T 3 , T 4 and T 5 , respectively.H. molitrix under T 2 showed minimum loss of 18.25 percent, while the maximum (31.03 percent) was under the influence of T 5 .C. carpio placed on T 1 , T 2 , T 3 , T 4 and T 5 showed the percentage losses as 43.49, 41.15, 44.40, 40.88 and 47.56, respectively, while in C. idella the minimum and maximum losses were 25.53 (under T 2 ) and 35.40 (under T 5 ) percent.In general, the percentage loss was inversely correlated with weight of fish i.e. the more healthy the fish, the lower the loss.
The percentage contributions of viscera towards losses during dressing for all the six fish species under all the five treatments are presented in table 3. The average total loss during the dressing of fish corresponded inversely to their live weight.Dressing percentage was always maximum for C. carpio, followed by C. catla, C. idella, C. mrigala and H. molitrix which was due to higher weights of viscera of C. carpio as compared to other fish species and correlated with body weight (table 3).This is a physiological rather than a genetic function since Bondari (1980) and Smitherman et al. (1983) found that progeny of catfish selected for body weight had dressing percentages similar to random controls.The results of the present study substantiate the findings of Viscera percentage seems to be the major variable explaining the dressing percentage.Dunham et al. (1985) reported viscera percentage was greater in young females than in young males.
The overall comparison of treatments showed broiler manure fertilization (T 2 ) to come up as the best treatment for meat/bone ratios of six fish species, followed by T 4 , T 1 , T 3 and T 5 as 24.73, 23.28, 20.88 and 17.93, respectively.Table 3 shows that meat/bone ratios were directly proportional to body weights.
The significant differences for meat/bone ratios of fish among both treatments and species were due to the effect of treatments on different final weights which were inversely correlated with the meat/bone ratios of fish (table 3).C. idella came up as the best fish species for overall meat/bone ratios under the influence of five treatments as compared

Study of visceral organs
The overall comparison of six fish species under all the five experimental treatments showed higher gonad weight in C. carpio, followed by C. idella, H. molitrix, L. rohita, C. mrigala and C. catla.It was observed that in male fish gonad weight was significantly less as compared to female fish (C.carpio and C. idella).The results of the present study are substantiated by the findings of Delahunty and DeVlaming (1980) who indicated that ovary weight in goldfish increases with increasing body weight.
In most teleostean species gonadal weight depends, in part, on body weight.One of the most common ways to account for the effect of body size on gonadal size has been to represent it as percentage of body weight.The gonadosomatic index introduced by Mein (1927) has been as an indicator of relative gonadal development or activity.GSI presumes a constant arithmetic relationship of gonadal weight to body weight over the range of fish weight being sampled.
Table 5 shows the gonadosomatic indices of the six fish species under all the five treatments.The maximum GSI value was 32.63 for C. carpio under the feed supplementation (T 1 ), followed by T 4 .Thus, the fish developed proportionately larger gonad.It was noted the female C. carpio and C. idella showed the higher values of GSI which means that ovaries contributed more towards GSI than testis in male fishes.
The correlation coefficients were highly significant and positive under all the five treatments for the fish species.The maximum value of correlation coefficient (r=0.998) was observed with H. molitrix under the influence of T 2 (table 4).The hepatosomatic index, as a percentage of body weight, is shown in table 5.The maximum value for HSI remained 1.99 for C. idella followed by C. mrigala under the influence of T 1 .
In studies on other species Rutilus rutilus (Mann, 1976a) and Mastacembelus armatus (Gupta, 1974), the relationship between GSI and body weight was constant over a range of fish weights, thus gonadosomatic index may be legitimate expression of gonadal activity.Mahboob and Sheri (1997) reported gonadosomatic index to increase with body weight in C. idella this explanation seem to be in line with the results of the present study.But these results contradict the findings of Mann (1976b) who found gonosomatic index not to increase with body weight.The relationship between gonad weight and body weight was positively significant which showed the dependence of gonadal development on the body weight or vice versa.The present results showed higher values of "r" for the female; this indicates that the females of both species gained more weight than the males.These results are in line with the findings of Okera (1974).
The overall comparison of six fish species under different experimental treatments revealed that highest liver weight was observed for C. idella, closely followed by C.  5).Delahunty and DeVlaming (1980) mentioned that HSI does not change over the range of body weight suggesting that HSI is an appropriate expression of liver size.The results of the present study were substantiated by the findings of the above mentioned workers.In the dab Limanda limanda, HSI values vary throughout the year in both male and female fish (Htun-Han, 1978).HSI values in the dab were lowest during the post spawning season, suggesting that liver reserves were not seriously depleted during yolk formation.Mahboob and Sheri (1997) found HSI to be highest in the pre-spawning season and lowest in the post spawning season period of grass carp (Ctenopharyngodon idella).The latter explanation is in line with the results of the present study because fishes were dissected prior to spawning period.

Table 1 .
Interspecies ratio, initial weight, fork length and total length of six fish species Viscera percentage was influenced by sexual differences and body weight of the fish.Viscera percentage to live body weight was maximum in C. carpio, followed by C. idella, C. mrigala, L. rohita, C. catla and H. molitrix.Viscera percentage increased with body weight more in females (C.carpio and C. idella) which related to egg development than males(C.catla,L. rohita, C. mrigala and H. molitrix).

Table 3 .
Javed (1988)imolt (1971) fish meat, percentage of visceral weights with live body weight and bone:meat ratios of 6 fish species as influenced by different treatments other fish species.This significantly high meat/bone ratio of C. idella could be due to its inherited quality characteristics as it contains less bones and higher muscle content as compared to C. carpio, H. molitrix, C. catla, L. rohita and C. mrigala.Sharma and Simolt (1971)reported that snakeheads had very little in the way of bony tissue butJaved (1988)mentioned Labeo rohita contained less bones as compared to C. catla and C. mrigala.This difference of opinion with the latter study was because of comparison among major carps, Chinese carps and common carp instead of among major carps only.No reference pertaining to meat/bone ratios of H. molitrix, C. carpio, C. idella could be found for comparison in Pakistan.These findings could be presumed as bench mark value in respect to the meat/bone ratios of fish under local conditions. to

Table 4 .
Correlation coefficients among gonad weight, liver weight and body weight of six fish species carpio.Whereas, HSI remained highest in C. idella under T 1 (table

Table 5 .
Gonadosomatic Index (GSI) and Hepatosomatic Index (HSI) of six fish species under various fertilization schemes