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1.
Analysis of the gut content of 329 specimens of T. zillii (Cichlidae) collected from Lake Kinneret, has shown great variation in the sorts of food.A study of seasonal dynamics has proved the prevalence in the food of Chironomida pupae (Diptera) in winter and spring and of zooplankton forms in summer and autumn. The additional food consisted of the various groups of algae, the most frequently found being Cyanophyta (100%) and Pyrrophyta (64.16%). An extremely voraceous species, it consumes — while searching for its preferred food — anything that comes its way in the water: algae, scraps of macrophytes, autochthonous and allochthonous insects, and forms of benthic origin, such as Nematoda, Ostracoda, Porifera and Chironomida (larvae).The satiation index is high (between 4.08 and 5.63), in contradiction to the low values of the coefficient of condition (between 3.05 and 3.51), and with the slow rate of growth in Lake Kinneret. The main food of Tilapia zillii, consists of arthropod species with a chitin content (which is eliminated unchanged) of more than 50% of the total weight, and this may account for the poor exploitation of the trophic base.This species of fish may be considered as being detrimental to others (i.e. commercially important species) because of its successful competition for food, and not, as is often incorrectly assumed, because it is an aggressive consumer of their spawn and fry.  相似文献   

2.
Daphnia lumholtzi (Sars) was found in Lake Kinneret until the late nineteen-fifties. Lake Kinneret was the northern-most limit of the distribution of this species. It is suggested that fingerlings of grey mullets and Sarotherodon aureus that were introduced into Lake Kinneret caused the extinction of D. lumholtzi.  相似文献   

3.
Dicentrarchus labrax and Dicentrarchus punctatus is able to thrive and grow in fresh water ponds. In all experiments there was successful controlling of young Tilapia aurea in the experimental ponds in comparison to the control ones. The number of young T. aurea per female and per pond was significantly lower in the experimental ponds than in control ponds. In 1973 the average number of young T. aurea per female was 80 in the experimental ponds and 287 young in the control ponds. In 1974 the average number of T. aurea young per female was 48 in the experimental ponds and 586 young in the control ponds.The growth rate of D. punctatus and D. labrax was higher in fresh water (S = 0.5‰) than in nature (salt water).  相似文献   

4.
Aquarium-held bigmouth buffalo Ictiobus cyprinellus (Valenciennes) were fed the blue-green alga Spirulina platensis (Nordstedt) at a daily rate of 29 g dry weight/kg body weight for 28 days. Daily growth was 14 g/kg body weight, and food conversion was 2.0. Tilapia aurea (Steindachner) also was fed this blue-green alga; growth and food conversion were similar to those found for bigmouth buffalo. Fresh Spirogyra sp. fed to grass carp Ctenopharyngodon idella Valenciennes resulted in poor growth, and food conversion was about 10.  相似文献   

5.
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 μm, 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.  相似文献   

6.
Methods for induced spawning and artificial incubation of Tilapia nilotica and T. aurea are described. These methods were required for the production, in aquaria, of F1 hybrids between the two species. Spawning families were established in long aquaria from which sexually ripe individuals were selected for stripping by their “on heat” display coloration. Injections of pituitary hormones were not required. The fertilized eggs were incubated in a low speed “shaker”. At correct temperatures Tilapia fry may be produced by this artificial process all year round.  相似文献   

7.
The experiment was carried out in a coastal lake near Bergen, Norway. Two experimental groups of Atlantic salmon (Salmo salar) yearlings were fed with live zooplankton in an artificial current. A third group, given commercial dry food pellets, was used as a control. The offered zooplankton biomass reached a maximum in the second week of July. The caladoceran Daphnia longispina dominated the zooplankton at this moment. A stock breakdown for this species was soon observed. The salmon yearlings preferred cladocerans. At the height of the zooplankton occurrence, Daphnia became the only prey species observed in the stomachs — and a prey selection for larger individuals was observed when food was in surplus. Earlier in the period the salmon selected the largest individuals of two cladoceran species of different shape, pigmentation and size at the same time. In the experiment live zooplankton was recognised as a satisfactory food when it occurred in sufficient amounts, compared with commercial fry food pellets. Best mean growth rate of zooplankton-fed fish was 0.92 mm/day. Negative growth rate was observed when low zooplankton densities occurred.  相似文献   

8.
The diets and feeding guild structure of a freshwater reed belt fish assemblage (30 species) were examined in Lake Kitaura, part of the Lake Kasumigaura system, eastern Japan, from June to September in 2009 and 2010. Ontogenetic dietary shifts were recognized in 14 species, including several species (e.g., Cyprinus carpio, Tridentiger brevispinis and Hyporhamphus intermedius) targeted by local fisheries. Juveniles of these species generally fed on zooplankton, later switching to other prey items (e.g., benthic chironomid larvae, gammaridean amphipods, shrimps, juvenile fishes, diatoms and decomposing reeds) with growth. A cluster analysis based on dietary overlaps showed that the reed belt fish assemblage comprised five feeding guilds (plant, zooplankton, benthic invertebrate, terrestrial insect and fish feeders). Of these, zooplankton feeders were the most abundantly represented in terms of species numbers, suggesting that the main food items for the fish assemblage were zooplankton (e.g., cladocerans, and calanoid and cyclopoid copepods). Fish feeders included five species, of which one was an alien species introduced from another region in Japan (Opsariichthys uncirostris) and three were from foreign countries (Micropterus salmoides, Lepomis macrochirus macrochirus and Ictalurus punctatus).  相似文献   

9.
The rearing of fish in cages could greatly contribute to increasing fish production in existing inland waters. Although it presents numerous advantages, its limitations and possible inconveniences must be borne in mind. Well-developed technology is available mainly from the Democratic Republic of Germany, The Netherlands, Japan, the U.S.A., the U.S.S.R. and the Lower Mekong region. Research is currently pursued in numerous other countries, where the use of floating cages in fish culture is becoming increasingly diversified.The most popular fish species used in intensive cultural systems are Cyprinus carpio, Ictalurus punctatus and Salmo gairdneri. In the semi-intensive Asian systems, Barbus spp., Pangasius spp. and murrels are among the favourite cage-reared fishes. Tilapia aurea and Tilapia nilotica have also proved to be well adapted to cage culture. Polyculture is only rarely practised.Floating cages seem to be the best suited for fish culture in most cases. Net cages are the simplest in design and the cheapest to build. The escape of fish, however, always remains an eventuality which might lead to choosing more expensive designs. Maintenance of cages must be regular. For flexibility of exploitation, cages should not be too large. Their location within the water body can play an important role in keeping production high.At high stocking rates, artificial feeding of a well-adapted diet is a necessity. Optimum conversion rates require a well-adjusted daily ration, possibly fractioned. Mechanized feed distribution is to be encouraged as a labour-saving practice. Less intensive systems rely more on locally available wastes, such as trash fish, but the feeding rate then depends mostly on feed prices.Best growth is generally achieved by C. carpio and I. punctatus. Attainable maximum production is as high as 35 kg/m3/month under intensive management. However, generally, production averages from 5 to 30 kg/m3/month for these two species. S. gairdneri is less productive. T. aurea and T. nilotica have both a very good potential. Production in less intensive systems varies greatly according to management practices.  相似文献   

10.
The waters of Lake Quarun have undergone severe chemical changes in the last 50 years. Salinity has increased progressively and is now 38‰ in some regions of the lake. Tilapia zillii is the only species that has not been affected by the salinity increase. Mullet fry have been stocked in the lake since 1928. There has been a progressive increase in the average total production of mullet from 0.45 tons (1929–1932) to 128.25 tons (1966–1969), and to 291.67 tons (1975/76–1978/79). Length and age composition of mullets in Lake Quarun were studied. The growth in length and weight of Mugil cephalus showed that the fish were in better condition in Lake Quarun than in other coastal areas of Egypt.It is recommended that studies should continue to improve survival of transplanted mullet fry into the lake, and on the artificial propagation of mullets on site.  相似文献   

11.
Abstract –  Three sympatric whitefish ( Coregonus lavaretus (L.)) forms, one being pelagic and two benthic, segregate available habitat and food resources in subarctic Lake Muddusjärvi, northern Finland. Zooplankton availability in the lake, food composition, diet-overlap and growth of densely rakered (DR) whitefish were examined during June to September to explore the reasons for the small individual size of the pelagic form. DR whitefish used zooplankton as main food item and prey selection followed zooplankton species density proportions in the lake. Zooplankton density and water temperature was highest in July–August. The average lengths of Bosmina spp., Daphnia spp., Calanoida and Cyclopoida in DR whitefish stomach were higher than in zooplankton sample during June–September, except Calanoida in June. Diet-overlap between DR whitefish age groups was high at all months indicating intercohort resource competition. DR whitefish reached sexual maturity at 3 years of age and at the length of 12 cm, after which somatic growth almost ceased. Reason for the small average size and slow growth of DR whitefish were connected to high diet-overlap between age groups and early sexual maturation.  相似文献   

12.
This study evaluated the effects of the addition of microalgae (Ankistrodesmus gracilis and Haematococcus pluvialis) to the fish diet in improving the growth and optimal pigmentation (red carotenoid) of Hyphessobrycon eques. The basal mixed diets consisted of a formulated diet, supplemented with dried microalgae biomass of A. gracilis (1.5 g kg?1) and H. pluvialis (1.5 g kg?1). The live food diets contained zooplankton was cultured in open ponds, associated with microalgae. All the microalgae were cultured in the laboratory. No mortality was observed with any experimental diets. Fish performance results showed significant differences (P < 0.05) between the basal diet (BD) and the live food diet. The higher weight and total length were observed with mixed diets (BD + H. pluvialis and BD + A. gracilis). The mixed diets promoted more intense values of chroma (Cab*), lightness (L*) and redness (a*) to H. eques. Diaphanosoma birgei (Cladocera) represented more than 32% of zooplankton ingested by ornamental fish in live food (zooplankton and zooplankton + microalgae), and Argyrodiaptomus furcatus (Copepoda) was the species most ingested by H. eques in live food dietary treatment zooplankton. The feeding behaviour observed in the laboratory as well as the food preferences of H. eques was dependent on the zooplankton composition present in the used open ponds. This study showed that diets with microalgae and zooplankton were able to enhance the pigmentation of H. eques, being a good tool to benefit the culture management of this species.  相似文献   

13.
The proportion of males in single pair crosses between Tilapia nilotica females and T. aurea males was found to vary between 50 and 100%. There was no apparent influence of the T. aurea males on these proportions. In a similar test nine T. vulcani females were paired with T. aurea males, and the proportion of males in their hybrid offspring ranged between 93 and 98%. Two T. nilotica mothers of all-male hybrid broods mated with unselected T. nilotica males, and all their daughters also reproduced all-male hybrid broods when crossed with T. aurea males. The reciprocal cross of T. aurea females with T. nilotica males reproduced three males to each female offspring. Growth rate tests of the all-male T. nilotica × T. aurea hybrids, and the T. vulcani × T. aurea hybrids did not reveal heterosis.  相似文献   

14.
A synthetic enkephalin analog (Tyr-D-Trp-Ala-D-Phe-NH2) was administered to juvenile hybrid tilapia (Tilapia nilotica ×T. aurea) by immersing the fish for 15 minutes per week into one of two doses of the hormone for 8 weeks. Growth, food conversion efficiency, body weight, specific growth rate, food conversion efficiency and feed consumption were all significantly increased as a result of enkephalin treatment. The low dose (10µg/100 ml water) of enkephalin analog had a better stimulation effect than that of the high dose (100µg/100 ml water). Liver protein and protein/DNA ratio were higher in both treatment groups than in the control group. Tissue-body indices and muscle proximate composition were similar in the treatment and control groups. The growth stimulation in fish treated with the enkephalin analog was possibly mediated by an increase in growth hormone secretion.  相似文献   

15.
Seven isocaloric and isonitrogenous semi-purified diets which contained graded levels of calcium ranging from 0.17 to 3.20% were fed to fingerling Tilapia aurea for a period of 11 weeks. The fish were maintained in a flow-through aquarium system supplied with calcium-free well water. Growth, feed conversion and bone composition data indicated that between 0.17 and 0.65% dietary calcium was adequate for optimum growth and normal bone mineralization.  相似文献   

16.
The effects of different stocking rates and ratios of Tilapia aurea (Steindachner) in combination with Cichlasoma managuense (Günther) on tilapia recruitment and production were evaluated in 440 m2 ponds. The research was conducted at the National Fisheries Station in El Salvador, Central America.The tilapia AT value, the total weight of marketable tilapia (14 cm or larger) expressed as a percentage of the total weight of the whole tilapia population, averaged 96 or greater at a stocking ratio of 4:1 (fingerling tilapia: fingerling C. managuense) and at a stocking ratio of 8:1 (fingerling tilapia: adult C. managuense). Tilapia AT values at a stocking ratio of 8:1 (fingerling tilapia: fingerling C. managuense) ranged from 71–89.Highest estimated annual production of marketable tilapia (3611 kg ha?1) occurred at the highest stocking rate of 12000 tilapia ha?1 in populations with an average tilapia AT value of 98. Greatest weight gain of marketable tilapia (167 g of 1.17 g day?1) occurred at the lowest stocking rate of 6000 tilapia ha?1 in populations with an average tilapia AT value of 99.Estimated annual production of marketable C. managuense ranged from 212–414 kg ha?1. The average weight gain of marketable fish varied from 48–60 g (0.32–0.40 g day?1). The average C. managuense, AT value was 54, ranging from 29–84.The estimated production of marketable fish of both species at stocking rates of 6000, 9000 and 12000 tilapia ha?1 in populations with tilapia AT values of 96 or greater averaged 3295, 3290 and 4025 kg ha?1 per year, respectively.  相似文献   

17.
Abstract– Growth, population composition and reproduction of bream were studied in Lake Volvi from 1989 to 1991. Females had a higher growth in length (L∞=507 mm, k=0.094) than males (L∞=452 mm, k=0.102). Growth can be characterized as medium, due to low food sources (zooplankton and chironimids). Large specimens are scarce because of high fishing mortality and low growth rate. All males greater than three years old, longer than 135 mm and all females greater than four years old and longer than 150 mm were sexually mature. These values of age and size of first maturity are the lowest that have been reported for this species. The size of the spawning egg is independent of the body size.  相似文献   

18.
A supplementary feed containing 30% coffee pulp was evaluated for use in the culture of Tilapia aurea in El Salvador, Central America. A comparison of the coffee pulp feed with a feed containing all of the same ingredients except coffee pulp was made with T. aurea raised in 1.0-m3 cages suspended in a fertilized earthen pond. Survival was high in all treatments and there was no significant difference in average weight gain between groups of fish receiving the two experimental feeds. Production trials were conducted in 100-m2 fish pens and in 0.05-ha earthen ponds. Pen-raised fish receiving coffee pulp feed grew faster throughout the experiment, and total production was approximately twice that in control treatments. Highest production in pens was 1.25 kg/m2 per year. Results of production pond trials using T. aurea at 9 000/ha and stocked with the piscivorous Cichlasoma managuense yielded an estimated 3 392 kg/ha per year in fed treatments and 2 049 kg/ha per year in controls. Low feed conversion (1.92) and low feed cost resulted in an increase in net annual earnings of $251.00/ha.  相似文献   

19.
A shift towards oligotrophic conditions in Lake Michigan has led to concern that altered trophic pathways are leading to lower early life survival and recruitment for Lake Whitefish (Coregonus clupeaformis). This study evaluated ontogenetic shifts in age-0 Lake Whitefish diets and evaluated how feeding ecology and the amount of food eaten varied with prey abundance and composition at a site in southeastern Lake Michigan during 2014–2017. Although prey densities varied among years, cyclopoid copepods were overall the most abundant prey available. In turn, cyclopoids were the predominant prey item in diets each year, particularly for the smallest larval Lake Whitefish. However, there was a tendency for the importance of cyclopoids to decline somewhat in each diet index as fish grew and other prey such as calanoid copepods, Bosminidae, Daphniidae and/or chironomids increased in importance. High zooplankton abundance, especially high cyclopoid abundance, available to the small size groups of Lake Whitefish (<21 mm) in 2014 was associated with high food mass/fish, high number of zooplankton eaten/fish, and low incidence of empty stomachs compared with 2015–2017. As fish grew, the impact of food abundance on prey consumption diminished somewhat, indicating that the relationship between fish feeding ecology and the prey environment can change quickly with fish size during the early life period.  相似文献   

20.
Intensive fishing of whitefish (Coregonus lavaretus) and a survival rate of the early stages of the fry that is generally too low lead, at present, to the whitefish stocks not being able to utilize fully the natural food resources now produced many times in excess of the requirements by the eutrophication of lakes.Feeding experiments in aquaria have, for several years, shown very impressively, that there are two main reasons for the high mortality of the larvae in the natural environment: high sensitivity to even a short-term lack of food and specific food requirements — the necessity for the larvae to feed on the juvenile stages of certain zooplanktonic crustaceans.Artificial breeding of whitefish eggs in cold water at 1°C caused a delay in hatching of about 8 weeks compared with natural hatching, thus allowing the release of the larvae at a time when the density of zooplankton is about ten times higher and mainly juvenile stages of crustaceans needed by the whitefish larvae are present. Hence, this is one proven way of improving the survival rate of whitefish larvae in the natural environment.Young fish, after metamorphosis, have less specialized food requirements than the larval stage and can even be fed adequately with dry food. In rearing the larvae, natural zooplankton can be replaced by the nauplii of the brine shrimp, Artemia salina. Larvae have not yet been reared on dry food or even on slowly frozen zooplankton or Artemia, but Artemia nauplii shock-frozen in liquid nitrogen (at ?196°C) were found to be as acceptable as living ones and allowed metamorphosis of the larvae to take place. The substance, assumed to be present in the living Artemia, which was lost on slow-freezing but retained after shock-freezing and was shown to be essential to the whitefish larvae, was insoluble in water. Biochemical investigation and identification of this substance are urgently required in order to synthesize an artificial complete food for whitefish larvae.As long as this artificial food is not available, attention will have to be focussed on rearing the larvae in natural ponds where the specific and essential zooplankton can be encouraged.  相似文献   

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