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Gut contents of silver carp — Hypophthalmichthys molitrix (Val.) — and some trophic relations to other fish species in a polyculture system
Aquaculture, ll(1977) 137-146 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
137
GUT CONTENTS OF SILVER CARP .-- HYPOPHTHALMICHTHYS MOLITRIX (VAL.) - AND SOME TROPHIC RELATIONS TO OTHER FISH SPECIES IN A POLYCULTURE SYSTEM
PEPIETTA
SPATARU
Fish and Aquaculture
Research Station, Dor (Israel)
Agricultural Research Organization,
Bet Dagan, Contribution
no. 308-E
(Received 21 January 1977)
ABSTRACT Spataru, P., 1977. Gut contents of silver carp - Hypophthalmichthys molitrix (Val.) and some trophic relations to other fish species in a polyculture system. Aquaculture, 11: 137-146. This work is a continuation of the studies conducted in the ponds of the Fish and Aquaculture Research Station, Dor, in 1975 concerning the components of fish feed under conditions of polyculture, with additional food and intensive fertilization. A study was made of the food eaten by the silver carp, Hypophthalmichthys molitrix (Val.), grown with or without supplementary food in ponds that had previously been used for storage of fish fed on pellets (ponds Types 1 and 3), or which had been kept dry for various periods of time (ponds Types 2 and 4). The special pattern of its gills, which are adapted to retain suspended organisms and particles of sizes less than 20 pm, enables the silver carp to filter enormous quantities of phytoplankton and organic particles. A comparative study was made of the trophic relations existing between Hypophthalmichthys molitrix (Val.), Cyprinus carpio (L.) and Tilapia aurea Steindachner, which were the principal species in the polyculture system, and of the influence of the type of pond used on the growth of the fish.
INTRODUCTION
As a continuation of the research at the Fish and Aquaculture Research Station at Dor on the behaviour of fish under polycultural conditions with respect to natural and additional foods (Spataru, 1976; Spataru and Hepher, 1977), the work described in this paper was devoted to the study of silver carp. The study was also concerned with the influence of this species on other fish species in the polyculture system and how it varied according to the condition of the pond before the beginning of the experiments and according to the additional food. Hypophthalmichthys molitrix (Val.), family Cyprinidae, originally a far east
138
Asian species, was introduced to Israeli ponds comparatively recently, at the Dor Research Station in 1966 (Yashouv, 1970). Known to be phytoplanktonophagous, this species was introduced in order to utilize the rich microflora of the ponds and thus complement other species in the polyculture system. In view of the favourable influence of raising silver carp in polyculture on carp production in particular and on fish production in general (Sarig, 1970; Yashouv, 1970, 1971,1972; Yashouv and Halevy, 1972), the method was extended to all fish ponds in the country. Both physiological features, the position of the mouth, the specialized branchial system and the length of the intestine, and the intestinal contents indicate that, Hypophthalmichthys is a phytoplanktonophagous fish. However, some authors have mentioned zooplankton, detritus, suspended organic particles, macrophytes and supplementary food as alternative foods for the silver carp (Lin, 1969; Sukumaran et al., 1970; Hickling, 1971; Bardach et al., 1972; Grygierek, 1973; Januszko, 1974; Kajak et al., 1975; Woynarovich, 1975) MATERIALS
AND METHODS
Material was collected from eight ponds, each one measuring 400 m* in area and 1 m in depth. In each pond, genetic lines of Cyprinus carpio L., Ctenopharingodon idella (Val.), Tilapia aurea Steindachner and hybrids of Tilapia aurea (male) X Tilapia uulcani Trew (female) were introduced in addition to the silver carp. In the same ponds, studies had been initiated by a team of geneticists (headed by Professor Ram Moav); the material obtained for the determination of gut contents as well as the data on the weight increase of fish originate from these experiments. In four of the eight ponds sorghum and fluid manure were added daily, and in the other four, fluid manure only; the quantities administered were increased as the fish grew (Wohlfarth et al., 1976). Standard fertilization with 2 kg superphosphate, 2 kg ammonium sulphate and 10 kg chicken droppings per pond was carried out twice a month. The ponds were stocked at the beginning of July and emptied on November 6th, 1975. Before they were stocked some of the ponds had been kept dry for various periods of time, while the others had been used to store fish that were fed with pellets containing 25% protein. Material was collected on five dates: July 30th (D I), August 13th (D II), September 17th (D III), October 1st (D IV) and October 15th (D V). At each collection and from every pond we examined four specimens of silver carp in the second year of growth (l+) and four specimens in the first year of growth (O+). The fish were sampled about 20 h after administration of food and manure and were immediately weighed and measured. The intestines were put into a 10% form01 solution. The intestinal contents were weighed and then examined under a Wild M 5 stereo microscope and a Wild M 20 microscope. In order to determine the degree of utilization of the ingested food, each intestinal tract was analysed in segments of 20 cm, and the contents of the
139
front and back extremities of the intestine were analysed separately. In this way a clear picture of the elements used as food was obtained. Qualitative and quantitative (gravimetric and numeric) methods were used to determine the food constituents. The number of algae ingested by each fish was estimated using the SedwichRafter counting cell and Utermohl’s eyepiece (Utermohl, 1958). The weight of the ingested algae was calculated from the volume of the cells of each species (Berman and Pollingher, 1974). To estimate the degree of satiation (index of fullness) of the gut the following formula was used. Index of fullness of gut = w X 100/W where w is the weight of the gut contents RESULTS
AND
and W is the weight of the fish.
DISCUSSION
Analysis of the intestinal content of the silver carp in our experiments showed it to have relatively uniform feeding habits and an aptitude to filter the microseston, the macroseston and the trypton. The special pattern of its gill rakers (Boulenger, 1901; Fang, 1928; Lin, 1969; Wilamovski, 1972) which are adapted to retain organisms and suspended particles smaller than 20 pm, enables Hypophthalmichthys molitrix to filter enormous quantities of phytoplankton and suspended particles. Some zooplankton also pass through its intestine without, however, being digested. Table I gives a list of items found in the intestinal contents, their frequency and the percentage of fish in which certain food species were dominant. It appears that only Scenedesmus quadricauda and organic particles are food for the silver carp. The other species of algae and the zooplankton are only additional forms which were ingested at the same time. Moreover, while examining the intestine by segments, it was observed that Euglena spp. and Phacus spp. had remained whole and that their pigmentation was retained all through the gut to the anus. Therefore, these species are not components of the food of Hypophthalmichthys. Zooplankton, represented in the present instance by Rotaria sp. and Brachionus sp., were found alive in the contents (not treated with formaldehyde solution) of the final segment of Hypophthalmichthys molitrix intestines. In closed cultures, with no contact with the air, these specimens of Rotifera continued to multiply, even 2 months after passing through the intestine. In the fixed material, both Rotariu sp. and Bruchionus sp. were found intact but strongly contracted as a result of treatment with formaldehyde solution. From the data in Table I it appears that the kind of food eaten varies with the type of pond in which the fish were raised. Thus, in Type 1 ponds (sorghum and fluid manure) or Type 3 ponds (fluid manure alone), which prior to the experiments had been used for storage of fish fed on pellets, the great abundance of phytoplankton was reflected in the intestinal contents of
I
5.66
28.30 24.52 18.86 7.54
-
_ -
-
5.66 18.86 11.32 -
26.41 15.09 18.86 11.32 5.66 5.66
24.52 -
26.41 26.41 11.32 11.32 3.11 1.88 1.88 1.88
Frequency (%) Dominance (%) 9.43
18.86 -
_ -
-
24.52 13.20 11.32 5.66 ~____~~~
-
1.88 1.88
22.64 13.20 11.32 1.88 1.88 1.88 -
Frequency (%) . ,
___
-
-
-
~. ~~~
9.43
13.20 -
Dominance (%)
(Type 3) -~~
(5pe 2) -___
Dominance (%)
Storage of fish fed with pellets
Fluid manure
Dry
Frequency (%)
Storage of fish fed with pellets (Type 1)
Previous treatment of ponds
Sorghum + fluid manure
Type of pond -
*Dominance is expressed by the percentage of examined fish in which a certain form of food was dominant.
Scenedesmus quadricauda Scenedesmus arcuatus Pediastrum duplex Pediastrum simplex Coelastrum sp. Ankistrodesmus sp. Spirogyra sp. Microcystis sp. Oscilla toria sp. Spirulina sp. Euglena sp. Phacus sp. Organic particles in suspension Botifera
Form of food
The frequency (%) and dominance (%)* of the various foods found in the intestinal contents of silver carp raised in four different types of pond _---___ -__ ____
TABLE
4)
18.86 9.43 13.20 -
-
7.54
20.75 20.75 15.09 3.77 5.66 5.66 -
Frequency (%)
(Spc
Dry
-_
13.20 -
-
-
-
11.32 -
Dominance (%)
141
the fish; algae were found in large quantities. In Type 1 ponds, Scenedesmus quadricauda was dominant in 24.52% of all the examined fish, and in none of them was any organic particle found. In Type 3 ponds this alga was dominant in only 13.20% of the examined fish. On the other hand, some of the fish preferred to feed on organic particles in suspension (9.43%). In Type 2 ponds, where food was administered but which had been kept dry for several weeks prior to the start of the experiments, the above-mentioned algal species was dominant in only 9.43% of all the silver carp examined, while suspended particles were dominant in 18.86% of these fish. In Type 4 ponds, where no food was administered and which had been kept dry for several days prior to the experiments, there was predominant consumption of Scenedesmus quadricauda by 11.32% of all fish examined, and of suspended particles by 13.20%. In the intestinal contents of the fish that had fed on algae exclusively, the number of ingested cells was of the order of 10” and 10” (Table II). There were some slight variations, but they were dependent only on the size of the fish and on the type of pond from which the samples had been taken. The fact that the type of pond has an important influence on the feeding habits of the fish, is also evident from the data in Table III, showing the weight increase of the principal species of fish in the polyculture system. Thus, in Type 3 ponds the silver carp grew most (535-583 g), thanks to the abundance in the ponds of suitable algae. Tilupiu aurea grew well, by consuming bottom-dwelling organisms in the pond (Chironomidae, Oligochaeta). As a consequence, Cyprinus carpio was deficient in growth because of lack of food and due to the competition presented by Tilapia. In Type 1 ponds there was a balance among the species in the polyculture. The algae ensured the growth of the silver carp, some of the benthos and the detritus served as food for the Tilupia and the common carp, while the latter species fed on sorghum as well. In Type 2 ponds there was no such balance because of the insufficient quantity of algae which, in turn, was due to the fact that the ponds had previously been kept dry for a prolonged period of time. In the absence of algae the silver carp filtered organic particles while they were in suspension before they settled to the bottom of the ponds. This was reflected in the smaller growth rate of the silver carp and Tilapia, while the common carp gained well in weight on account of the supplementary food. In Type 4 ponds, in which no food was administered and which had been kept dry prior to the start of the experiment, there was a very poor supply of phytoplankton, zooplankton and zoobenthos and the poorest results were obtained with silver carp, common carp and Tilapiu. An examination of the satiation indices (Fig.1) led to similar conclusions: in ponds which had been used for storage of fish fed on pellets and where trophic chains had therefore not been interrupted, the silver carp fed better.
II
3” 4 4
1 1 2 2
of pond*
38 .109 2 .lO” 287 .lO* 185 .lO’ 422.510’ 214 .lO* 21 .109 15 ,109
Number of algae
Scenedesmus _~_
152 .lOP 8 .lO’e 114.5109 74 .109 171 .109 855 .10* 84 .10* 59 ,109
Number of cells
quadricauda
Species of algae
*See Table I for description.
1+ o+ 1+ o+ 1+ o+ 1+ o+
-____
of fish
___________ Age Type
30.4 16.2 22.9 14.8 34.2 17.1 16.8 11.8
Weight (g) 315105 675.106 17.10’ 17.10’ 15.10* 675~10~ 35.10’ 17.107
Number of algae
Scenedesm
126.106 27.10’ 67.10’ 67.10’ 6.109 27109 14.10’ 67.10’ 2.5 0.4 0.1 0.1 0.9 0.4 0.2 0.1
2.108 11.10’ 75.106 5.107 5.10’ 5.10’ 75.106 11.10’
Number of algae
Number of cells Weight (9)
Pediastrum
~-
us arcua tus
____
~-
2.109 11.10” 75.10’ 5.10’ 5.10’ 5.10’ 75.10’ 11.10’
Number of cells
spp.
The maximum number and the weight of the principal algae ingested, according to the age of the fish and type of pond
TABLE
0.4 0.2 0.15 0.1 0.1 0.1 0.15 0.2
Weight (g)
_
715.106 22.10’ 36.106 2210’ 14.10’ 14-107 164.106 715.101
Number of algae
Euglena spp.
0.93 0.30 0.05 0.30 0.20 0.20 0.25 0.10
Weight (9)
III
*See Table I for description.
o+ 1+ o+ 1+
Hypophthalmichthys Hypophthalmichthys Cyprinus carpio TiJapia aurea
molitrix molitrix
Age
Species of fish
45.0 465.0 32.5 97.0
Initial average weight (9)
401 -580 716 -1 048 249.5-440.5 438 -510
Final average weight (g)
468 505 390 413
Type 1
--___
432 479 408 354 ~~
5pe
_~__
-_-~
Type 3 535 583 232 347 .._~~~~
2
Weight increase (g) in ponds*
356 251 217 341
Type 4
Weight increases of silver carp, common carp and TiJapia under different feeding regimes and in different types of pond _-
TABLE
144
Type
I
ponds
Type
2
ponds
----
Type
3
ponds
.. .. . . . . ..
Type
4
ponds
_
\
I
I 01
I D11
I D ttt
1 DtV
I
. . -.._
DV
Fig.1. Satiation index of silver carp, July 30th-October
15th 1975.
The values for the whole period of observation in ponds Types 1 and 3 show the stable character of feeding, with extremely slight variations. In Type 1 ponds the values of the satiation index varied between 2.65 and 3.29, and in Type 3 ponds they varied between 2.58 and 3.75. In Type 2 ponds the variation was considerable (between 1.23 and 3.66), the increase probably being attributable to the quantities of sorghum administered throughout the experiment. The sorghum decomposed in the water, leading to an increase in the amount of material in suspension, which was then used by the silver carp. The very low values of the satiation index in Type 4 ponds on the one hand, indicate the insufficient quantity of natural food available and, on the other hand, explain the deficit in growth of the silver carp. Our observations are in accordance with those made previously with regard to the behaviour and the “mutual interrelation” of fish in polyculture (Yashouv, 1970; Marek, 1976). Yashouv (1971) and Yashouv and Helevy (1972) have pointed out that there is a “beneficial interrelation” between common carp and silver carp, as each species indirectly stimulates the growth of the other. In our opinion, these interrelations remain beneficial as long as sufficient quantities of natural and supplementary food are available in the ponds. A lack of any natural food item will always lead to a deficiency in growth of the Cyprinidae species (which have no stomach and are consequently deficient in enzymes), irrespective of the quantity of supplementary food available. Our conclusions are as follows: (1) Considering the nature of the food of the silver carp which is a consumer of phytoplankton and suspended organic particles, it is advisable that ponds not be dried prior to stocking. In this way, owing to the continuity of the trophic chains - the natural trophic basis - a high production is ensured, not only of the silver carp, but also of the other species in a polyculture system. (2) If the fish are grown under conditions of insufficient supplementary food, the number of species in the polyculture system should be reduced, even if intensive fertilization is practised. The coexistence of common carp,
145
silver carp and Tilapia in the same ponds, under conditions of high density and insufficient supplementary food, will always lead to competition and, consequently, to sub-optimal growth of the fish. (3) To restore the flora and fauna of the ponds (the natural trophic basis) the basins should be filled with water and fertilized for a certain period of time before they are stocked. ACKNOWLEDGEMENTS
The author expresses her thanks to the team of research workers headed by Professor R. Moav for the material and data pertaining to fish breeding made available to her for the preparation of this paper. The assistance of Mr M. Zorn in collecting the material required for the preparation of this paper is gratefully acknowledged.
REFERENCES Bardach, J., Ryther, J. and McLarney, W., 1972. Aquaculture. The Farming and Husbandry of Freshwater and Marine Organisms. J. Wiley and Sons, New York, N.Y., London, Sydney, N.S.W., Toronto, Ont., 868 pp. Berman, T. and Pollongher, U., 1974. Annual and seasonal variations of phytoplankton, chlorophyll and photosynthesis in Lake Kinneret. Limnol. Oceanogr., 19 (1): 31-54. Boulenger, G., 1901. On the presence of a suprabranchial organ in the Hypophthalmichthys Ann. Mag. Nat. Hist. 8 (7): 186-188. Fang, P.W., 1928. Notes on the gill-rakers and their structures of Aristichthys nob& and Hypophthalmichthys molitrix. Contrib. Biol. Lab. Sci. Sot. China, 4 (5): l-30. Grygierek, E., 1973. The influence of phytophagous fish on pond zooplankton. Aquaculture, 2 (2): 197-208. Hickling, CF., 1971. Fish Culture. Faber and Faber, London, 2nd edn, 317 pp. Januszko, M., 1974. The effect of three species of phytophagous fish on algae development. Pol. Arch. Hydrobiol., 21: 431--454. Kajak, Z., Rybek, J.I., Spondniewska, I. and Godliewska-Lipowa, W., 1975. Influence of planktonivorous fish Hypophthalmichthys molitrix (Val.) on the plankton and benthos of the eutrophic lake. Pol. Arch. Hydrobiol. 22 (2): 301-310. Lin, S.Y., 1969. The feeding habits of silver carp, bighead and mud carp. Jt Comm. Rural Reconstr. Taipei, Taiwan, China, Fish. Ser., 8 : 49-66. Marek, M., 1976. For and against polyculture in fish ponds. Daig Umidgeh, 11 (2): 8-10 (in Hebrew with English summary). Sarig, S., 1970. Initial results of silver carp (Hypoph thalmich thys molitrix) breeding in israeli fishponds in 1969. Bamidgeh, 22 (4): 95-100. Spataru, P., 1976. Natural feed of Tilupia aurea Steindachner in polyculture with supplementary feed and intensive manuring. Bamidgeh, 28 (3): 57-3. Spataru, P. and Hepher, B., 1977. Common carp predating on Tilapia fry in a fishpond under a high density polyculture system. Bamidgeh, 29 (1): 25-28. Sukumaran, K.K., Singh, S.B., Murty, D.S. and Chakrabarti, P.C., 1970. Studies on compatibility and competition between silver carp, Hypophthalmichthys molitrix (Val.) and catla, Catla catla (Ham.). Proc. Indo-Pac. Fish. Cont. Tech.Pap. Sect. II, 13 (2): 185-194.
146
Utermohl, H., 1958. Zur Vervollkommung der quantitativen Phytoplanktonmethodic. Mitt. Int. Ver. Theor. Angew. Limnol., 9, 38 pp. Wilamovski, A., 1972. The structure of the gill apparatus and the suprabranchial organ of Hypophthalmichthys molitrix Val. (silver carp). Bamidgeh, 24 (4): 87-98. Wohlfarth, G., Hulata, G., Barash, H., Lahman, M., Moav, R., Abramson, Z. and Brody, T., 1976. Summary of the integrated research in polyculture, feeding, intensive manuring and genetic improvement carried out in 1974-1975. Daig Umidgeh, 11 (2): 11-32 (in Hebrew with English summary). Woynarovich, E., 1975. Elementary Guide to Fish Culture in Nepal. FAO, Rome, 131 pp. Yashouv, A., 1970. Hypophthalmichthys molitrix (Val.) - silver carp in fish ponds of the Fish Culture Research Station at Dor. Daig Umidgeh, 5 (2): 12-25 (in Hebrew with English summary). Yashouv, A., 1971. Interaction between the common carp (Cyprinus carpio) and the silver carp (Hypophtholmichthys molitrix) in fish ponds. Bamidgeh, 23 (3): 85--92. Yashouv, A., 1972. The carrying capacity and ecological niche as management concepts of fish production in ponds. In: Z. Kajak and A. Hillbricht-Ilkowska (Editors), Proc. IBP-UNESCO Symp. Productivity Problems of Freshwaters. Pafistwowe Wydawnictwo Naukowe, Warszawa, Krakow, pp. 573-578. Yashouv, A. and Halevy, A., 1972. Experimental studies of polyculture in 1971. Bamidgeh, 24 (2): 31-39.
137
GUT CONTENTS OF SILVER CARP .-- HYPOPHTHALMICHTHYS MOLITRIX (VAL.) - AND SOME TROPHIC RELATIONS TO OTHER FISH SPECIES IN A POLYCULTURE SYSTEM
PEPIETTA
SPATARU
Fish and Aquaculture
Research Station, Dor (Israel)
Agricultural Research Organization,
Bet Dagan, Contribution
no. 308-E
(Received 21 January 1977)
ABSTRACT Spataru, P., 1977. Gut contents of silver carp - Hypophthalmichthys molitrix (Val.) and some trophic relations to other fish species in a polyculture system. Aquaculture, 11: 137-146. This work is a continuation of the studies conducted in the ponds of the Fish and Aquaculture Research Station, Dor, in 1975 concerning the components of fish feed under conditions of polyculture, with additional food and intensive fertilization. A study was made of the food eaten by the silver carp, Hypophthalmichthys molitrix (Val.), grown with or without supplementary food in ponds that had previously been used for storage of fish fed on pellets (ponds Types 1 and 3), or which had been kept dry for various periods of time (ponds Types 2 and 4). The special pattern of its gills, which are adapted to retain suspended organisms and particles of sizes less than 20 pm, enables the silver carp to filter enormous quantities of phytoplankton and organic particles. A comparative study was made of the trophic relations existing between Hypophthalmichthys molitrix (Val.), Cyprinus carpio (L.) and Tilapia aurea Steindachner, which were the principal species in the polyculture system, and of the influence of the type of pond used on the growth of the fish.
INTRODUCTION
As a continuation of the research at the Fish and Aquaculture Research Station at Dor on the behaviour of fish under polycultural conditions with respect to natural and additional foods (Spataru, 1976; Spataru and Hepher, 1977), the work described in this paper was devoted to the study of silver carp. The study was also concerned with the influence of this species on other fish species in the polyculture system and how it varied according to the condition of the pond before the beginning of the experiments and according to the additional food. Hypophthalmichthys molitrix (Val.), family Cyprinidae, originally a far east
138
Asian species, was introduced to Israeli ponds comparatively recently, at the Dor Research Station in 1966 (Yashouv, 1970). Known to be phytoplanktonophagous, this species was introduced in order to utilize the rich microflora of the ponds and thus complement other species in the polyculture system. In view of the favourable influence of raising silver carp in polyculture on carp production in particular and on fish production in general (Sarig, 1970; Yashouv, 1970, 1971,1972; Yashouv and Halevy, 1972), the method was extended to all fish ponds in the country. Both physiological features, the position of the mouth, the specialized branchial system and the length of the intestine, and the intestinal contents indicate that, Hypophthalmichthys is a phytoplanktonophagous fish. However, some authors have mentioned zooplankton, detritus, suspended organic particles, macrophytes and supplementary food as alternative foods for the silver carp (Lin, 1969; Sukumaran et al., 1970; Hickling, 1971; Bardach et al., 1972; Grygierek, 1973; Januszko, 1974; Kajak et al., 1975; Woynarovich, 1975) MATERIALS
AND METHODS
Material was collected from eight ponds, each one measuring 400 m* in area and 1 m in depth. In each pond, genetic lines of Cyprinus carpio L., Ctenopharingodon idella (Val.), Tilapia aurea Steindachner and hybrids of Tilapia aurea (male) X Tilapia uulcani Trew (female) were introduced in addition to the silver carp. In the same ponds, studies had been initiated by a team of geneticists (headed by Professor Ram Moav); the material obtained for the determination of gut contents as well as the data on the weight increase of fish originate from these experiments. In four of the eight ponds sorghum and fluid manure were added daily, and in the other four, fluid manure only; the quantities administered were increased as the fish grew (Wohlfarth et al., 1976). Standard fertilization with 2 kg superphosphate, 2 kg ammonium sulphate and 10 kg chicken droppings per pond was carried out twice a month. The ponds were stocked at the beginning of July and emptied on November 6th, 1975. Before they were stocked some of the ponds had been kept dry for various periods of time, while the others had been used to store fish that were fed with pellets containing 25% protein. Material was collected on five dates: July 30th (D I), August 13th (D II), September 17th (D III), October 1st (D IV) and October 15th (D V). At each collection and from every pond we examined four specimens of silver carp in the second year of growth (l+) and four specimens in the first year of growth (O+). The fish were sampled about 20 h after administration of food and manure and were immediately weighed and measured. The intestines were put into a 10% form01 solution. The intestinal contents were weighed and then examined under a Wild M 5 stereo microscope and a Wild M 20 microscope. In order to determine the degree of utilization of the ingested food, each intestinal tract was analysed in segments of 20 cm, and the contents of the
139
front and back extremities of the intestine were analysed separately. In this way a clear picture of the elements used as food was obtained. Qualitative and quantitative (gravimetric and numeric) methods were used to determine the food constituents. The number of algae ingested by each fish was estimated using the SedwichRafter counting cell and Utermohl’s eyepiece (Utermohl, 1958). The weight of the ingested algae was calculated from the volume of the cells of each species (Berman and Pollingher, 1974). To estimate the degree of satiation (index of fullness) of the gut the following formula was used. Index of fullness of gut = w X 100/W where w is the weight of the gut contents RESULTS
AND
and W is the weight of the fish.
DISCUSSION
Analysis of the intestinal content of the silver carp in our experiments showed it to have relatively uniform feeding habits and an aptitude to filter the microseston, the macroseston and the trypton. The special pattern of its gill rakers (Boulenger, 1901; Fang, 1928; Lin, 1969; Wilamovski, 1972) which are adapted to retain organisms and suspended particles smaller than 20 pm, enables Hypophthalmichthys molitrix to filter enormous quantities of phytoplankton and suspended particles. Some zooplankton also pass through its intestine without, however, being digested. Table I gives a list of items found in the intestinal contents, their frequency and the percentage of fish in which certain food species were dominant. It appears that only Scenedesmus quadricauda and organic particles are food for the silver carp. The other species of algae and the zooplankton are only additional forms which were ingested at the same time. Moreover, while examining the intestine by segments, it was observed that Euglena spp. and Phacus spp. had remained whole and that their pigmentation was retained all through the gut to the anus. Therefore, these species are not components of the food of Hypophthalmichthys. Zooplankton, represented in the present instance by Rotaria sp. and Brachionus sp., were found alive in the contents (not treated with formaldehyde solution) of the final segment of Hypophthalmichthys molitrix intestines. In closed cultures, with no contact with the air, these specimens of Rotifera continued to multiply, even 2 months after passing through the intestine. In the fixed material, both Rotariu sp. and Bruchionus sp. were found intact but strongly contracted as a result of treatment with formaldehyde solution. From the data in Table I it appears that the kind of food eaten varies with the type of pond in which the fish were raised. Thus, in Type 1 ponds (sorghum and fluid manure) or Type 3 ponds (fluid manure alone), which prior to the experiments had been used for storage of fish fed on pellets, the great abundance of phytoplankton was reflected in the intestinal contents of
I
5.66
28.30 24.52 18.86 7.54
-
_ -
-
5.66 18.86 11.32 -
26.41 15.09 18.86 11.32 5.66 5.66
24.52 -
26.41 26.41 11.32 11.32 3.11 1.88 1.88 1.88
Frequency (%) Dominance (%) 9.43
18.86 -
_ -
-
24.52 13.20 11.32 5.66 ~____~~~
-
1.88 1.88
22.64 13.20 11.32 1.88 1.88 1.88 -
Frequency (%) . ,
___
-
-
-
~. ~~~
9.43
13.20 -
Dominance (%)
(Type 3) -~~
(5pe 2) -___
Dominance (%)
Storage of fish fed with pellets
Fluid manure
Dry
Frequency (%)
Storage of fish fed with pellets (Type 1)
Previous treatment of ponds
Sorghum + fluid manure
Type of pond -
*Dominance is expressed by the percentage of examined fish in which a certain form of food was dominant.
Scenedesmus quadricauda Scenedesmus arcuatus Pediastrum duplex Pediastrum simplex Coelastrum sp. Ankistrodesmus sp. Spirogyra sp. Microcystis sp. Oscilla toria sp. Spirulina sp. Euglena sp. Phacus sp. Organic particles in suspension Botifera
Form of food
The frequency (%) and dominance (%)* of the various foods found in the intestinal contents of silver carp raised in four different types of pond _---___ -__ ____
TABLE
4)
18.86 9.43 13.20 -
-
7.54
20.75 20.75 15.09 3.77 5.66 5.66 -
Frequency (%)
(Spc
Dry
-_
13.20 -
-
-
-
11.32 -
Dominance (%)
141
the fish; algae were found in large quantities. In Type 1 ponds, Scenedesmus quadricauda was dominant in 24.52% of all the examined fish, and in none of them was any organic particle found. In Type 3 ponds this alga was dominant in only 13.20% of the examined fish. On the other hand, some of the fish preferred to feed on organic particles in suspension (9.43%). In Type 2 ponds, where food was administered but which had been kept dry for several weeks prior to the start of the experiments, the above-mentioned algal species was dominant in only 9.43% of all the silver carp examined, while suspended particles were dominant in 18.86% of these fish. In Type 4 ponds, where no food was administered and which had been kept dry for several days prior to the experiments, there was predominant consumption of Scenedesmus quadricauda by 11.32% of all fish examined, and of suspended particles by 13.20%. In the intestinal contents of the fish that had fed on algae exclusively, the number of ingested cells was of the order of 10” and 10” (Table II). There were some slight variations, but they were dependent only on the size of the fish and on the type of pond from which the samples had been taken. The fact that the type of pond has an important influence on the feeding habits of the fish, is also evident from the data in Table III, showing the weight increase of the principal species of fish in the polyculture system. Thus, in Type 3 ponds the silver carp grew most (535-583 g), thanks to the abundance in the ponds of suitable algae. Tilupiu aurea grew well, by consuming bottom-dwelling organisms in the pond (Chironomidae, Oligochaeta). As a consequence, Cyprinus carpio was deficient in growth because of lack of food and due to the competition presented by Tilapia. In Type 1 ponds there was a balance among the species in the polyculture. The algae ensured the growth of the silver carp, some of the benthos and the detritus served as food for the Tilupia and the common carp, while the latter species fed on sorghum as well. In Type 2 ponds there was no such balance because of the insufficient quantity of algae which, in turn, was due to the fact that the ponds had previously been kept dry for a prolonged period of time. In the absence of algae the silver carp filtered organic particles while they were in suspension before they settled to the bottom of the ponds. This was reflected in the smaller growth rate of the silver carp and Tilapia, while the common carp gained well in weight on account of the supplementary food. In Type 4 ponds, in which no food was administered and which had been kept dry prior to the start of the experiment, there was a very poor supply of phytoplankton, zooplankton and zoobenthos and the poorest results were obtained with silver carp, common carp and Tilapiu. An examination of the satiation indices (Fig.1) led to similar conclusions: in ponds which had been used for storage of fish fed on pellets and where trophic chains had therefore not been interrupted, the silver carp fed better.
II
3” 4 4
1 1 2 2
of pond*
38 .109 2 .lO” 287 .lO* 185 .lO’ 422.510’ 214 .lO* 21 .109 15 ,109
Number of algae
Scenedesmus _~_
152 .lOP 8 .lO’e 114.5109 74 .109 171 .109 855 .10* 84 .10* 59 ,109
Number of cells
quadricauda
Species of algae
*See Table I for description.
1+ o+ 1+ o+ 1+ o+ 1+ o+
-____
of fish
___________ Age Type
30.4 16.2 22.9 14.8 34.2 17.1 16.8 11.8
Weight (g) 315105 675.106 17.10’ 17.10’ 15.10* 675~10~ 35.10’ 17.107
Number of algae
Scenedesm
126.106 27.10’ 67.10’ 67.10’ 6.109 27109 14.10’ 67.10’ 2.5 0.4 0.1 0.1 0.9 0.4 0.2 0.1
2.108 11.10’ 75.106 5.107 5.10’ 5.10’ 75.106 11.10’
Number of algae
Number of cells Weight (9)
Pediastrum
~-
us arcua tus
____
~-
2.109 11.10” 75.10’ 5.10’ 5.10’ 5.10’ 75.10’ 11.10’
Number of cells
spp.
The maximum number and the weight of the principal algae ingested, according to the age of the fish and type of pond
TABLE
0.4 0.2 0.15 0.1 0.1 0.1 0.15 0.2
Weight (g)
_
715.106 22.10’ 36.106 2210’ 14.10’ 14-107 164.106 715.101
Number of algae
Euglena spp.
0.93 0.30 0.05 0.30 0.20 0.20 0.25 0.10
Weight (9)
III
*See Table I for description.
o+ 1+ o+ 1+
Hypophthalmichthys Hypophthalmichthys Cyprinus carpio TiJapia aurea
molitrix molitrix
Age
Species of fish
45.0 465.0 32.5 97.0
Initial average weight (9)
401 -580 716 -1 048 249.5-440.5 438 -510
Final average weight (g)
468 505 390 413
Type 1
--___
432 479 408 354 ~~
5pe
_~__
-_-~
Type 3 535 583 232 347 .._~~~~
2
Weight increase (g) in ponds*
356 251 217 341
Type 4
Weight increases of silver carp, common carp and TiJapia under different feeding regimes and in different types of pond _-
TABLE
144
Type
I
ponds
Type
2
ponds
----
Type
3
ponds
.. .. . . . . ..
Type
4
ponds
_
\
I
I 01
I D11
I D ttt
1 DtV
I
. . -.._
DV
Fig.1. Satiation index of silver carp, July 30th-October
15th 1975.
The values for the whole period of observation in ponds Types 1 and 3 show the stable character of feeding, with extremely slight variations. In Type 1 ponds the values of the satiation index varied between 2.65 and 3.29, and in Type 3 ponds they varied between 2.58 and 3.75. In Type 2 ponds the variation was considerable (between 1.23 and 3.66), the increase probably being attributable to the quantities of sorghum administered throughout the experiment. The sorghum decomposed in the water, leading to an increase in the amount of material in suspension, which was then used by the silver carp. The very low values of the satiation index in Type 4 ponds on the one hand, indicate the insufficient quantity of natural food available and, on the other hand, explain the deficit in growth of the silver carp. Our observations are in accordance with those made previously with regard to the behaviour and the “mutual interrelation” of fish in polyculture (Yashouv, 1970; Marek, 1976). Yashouv (1971) and Yashouv and Helevy (1972) have pointed out that there is a “beneficial interrelation” between common carp and silver carp, as each species indirectly stimulates the growth of the other. In our opinion, these interrelations remain beneficial as long as sufficient quantities of natural and supplementary food are available in the ponds. A lack of any natural food item will always lead to a deficiency in growth of the Cyprinidae species (which have no stomach and are consequently deficient in enzymes), irrespective of the quantity of supplementary food available. Our conclusions are as follows: (1) Considering the nature of the food of the silver carp which is a consumer of phytoplankton and suspended organic particles, it is advisable that ponds not be dried prior to stocking. In this way, owing to the continuity of the trophic chains - the natural trophic basis - a high production is ensured, not only of the silver carp, but also of the other species in a polyculture system. (2) If the fish are grown under conditions of insufficient supplementary food, the number of species in the polyculture system should be reduced, even if intensive fertilization is practised. The coexistence of common carp,
145
silver carp and Tilapia in the same ponds, under conditions of high density and insufficient supplementary food, will always lead to competition and, consequently, to sub-optimal growth of the fish. (3) To restore the flora and fauna of the ponds (the natural trophic basis) the basins should be filled with water and fertilized for a certain period of time before they are stocked. ACKNOWLEDGEMENTS
The author expresses her thanks to the team of research workers headed by Professor R. Moav for the material and data pertaining to fish breeding made available to her for the preparation of this paper. The assistance of Mr M. Zorn in collecting the material required for the preparation of this paper is gratefully acknowledged.
REFERENCES Bardach, J., Ryther, J. and McLarney, W., 1972. Aquaculture. The Farming and Husbandry of Freshwater and Marine Organisms. J. Wiley and Sons, New York, N.Y., London, Sydney, N.S.W., Toronto, Ont., 868 pp. Berman, T. and Pollongher, U., 1974. Annual and seasonal variations of phytoplankton, chlorophyll and photosynthesis in Lake Kinneret. Limnol. Oceanogr., 19 (1): 31-54. Boulenger, G., 1901. On the presence of a suprabranchial organ in the Hypophthalmichthys Ann. Mag. Nat. Hist. 8 (7): 186-188. Fang, P.W., 1928. Notes on the gill-rakers and their structures of Aristichthys nob& and Hypophthalmichthys molitrix. Contrib. Biol. Lab. Sci. Sot. China, 4 (5): l-30. Grygierek, E., 1973. The influence of phytophagous fish on pond zooplankton. Aquaculture, 2 (2): 197-208. Hickling, CF., 1971. Fish Culture. Faber and Faber, London, 2nd edn, 317 pp. Januszko, M., 1974. The effect of three species of phytophagous fish on algae development. Pol. Arch. Hydrobiol., 21: 431--454. Kajak, Z., Rybek, J.I., Spondniewska, I. and Godliewska-Lipowa, W., 1975. Influence of planktonivorous fish Hypophthalmichthys molitrix (Val.) on the plankton and benthos of the eutrophic lake. Pol. Arch. Hydrobiol. 22 (2): 301-310. Lin, S.Y., 1969. The feeding habits of silver carp, bighead and mud carp. Jt Comm. Rural Reconstr. Taipei, Taiwan, China, Fish. Ser., 8 : 49-66. Marek, M., 1976. For and against polyculture in fish ponds. Daig Umidgeh, 11 (2): 8-10 (in Hebrew with English summary). Sarig, S., 1970. Initial results of silver carp (Hypoph thalmich thys molitrix) breeding in israeli fishponds in 1969. Bamidgeh, 22 (4): 95-100. Spataru, P., 1976. Natural feed of Tilupia aurea Steindachner in polyculture with supplementary feed and intensive manuring. Bamidgeh, 28 (3): 57-3. Spataru, P. and Hepher, B., 1977. Common carp predating on Tilapia fry in a fishpond under a high density polyculture system. Bamidgeh, 29 (1): 25-28. Sukumaran, K.K., Singh, S.B., Murty, D.S. and Chakrabarti, P.C., 1970. Studies on compatibility and competition between silver carp, Hypophthalmichthys molitrix (Val.) and catla, Catla catla (Ham.). Proc. Indo-Pac. Fish. Cont. Tech.Pap. Sect. II, 13 (2): 185-194.
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Utermohl, H., 1958. Zur Vervollkommung der quantitativen Phytoplanktonmethodic. Mitt. Int. Ver. Theor. Angew. Limnol., 9, 38 pp. Wilamovski, A., 1972. The structure of the gill apparatus and the suprabranchial organ of Hypophthalmichthys molitrix Val. (silver carp). Bamidgeh, 24 (4): 87-98. Wohlfarth, G., Hulata, G., Barash, H., Lahman, M., Moav, R., Abramson, Z. and Brody, T., 1976. Summary of the integrated research in polyculture, feeding, intensive manuring and genetic improvement carried out in 1974-1975. Daig Umidgeh, 11 (2): 11-32 (in Hebrew with English summary). Woynarovich, E., 1975. Elementary Guide to Fish Culture in Nepal. FAO, Rome, 131 pp. Yashouv, A., 1970. Hypophthalmichthys molitrix (Val.) - silver carp in fish ponds of the Fish Culture Research Station at Dor. Daig Umidgeh, 5 (2): 12-25 (in Hebrew with English summary). Yashouv, A., 1971. Interaction between the common carp (Cyprinus carpio) and the silver carp (Hypophtholmichthys molitrix) in fish ponds. Bamidgeh, 23 (3): 85--92. Yashouv, A., 1972. The carrying capacity and ecological niche as management concepts of fish production in ponds. In: Z. Kajak and A. Hillbricht-Ilkowska (Editors), Proc. IBP-UNESCO Symp. Productivity Problems of Freshwaters. Pafistwowe Wydawnictwo Naukowe, Warszawa, Krakow, pp. 573-578. Yashouv, A. and Halevy, A., 1972. Experimental studies of polyculture in 1971. Bamidgeh, 24 (2): 31-39.