IJA Volume 53, Issue 1, 2001
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ItemAlternative Protein Sources As Substitutes For Fishmeal In The Diet Of Young Tilapia Oreochromis Niloticus (LINN.)(Israeli Journal of Aquaculture - BAMIGDEH, 2001)Fifteen test diets were theoretically formulated to contain 33.32% dietary protein, dry matter, using a mixture of alternative protein sources and fishmeal in various proportions. Test diets were fed to fingerlings (initial weight 3.2±0.2 g) in triplicate tanks for eight weeks at 5% body weight per day in three portions. At the end of each experimental phase, fish carcass from the feeding groups was homogenized. Freeze-dried samples of fish at the beginning and end of the experiments as well as samples of the test diets were analyzed for proximate composition. Fish fed diet 1 containing 43% fishmeal recorded the highest weight gain, highest specific growth rate (SGR, 3.46%/d) and lowest food conversion ratio (FCR, 1.11). When part of the fishmeal was substituted with 18% soy- bean meal and 5% blood meal (diet 8), SGR and FCR were 3.02%/d and 1.34, respectively, not significantly different from diet 1 at 0.05 probability. Results showed that proper combination of alternative protein sources can provide 42-45% of the protein required by Oreochromis niloticus (33.32% dietary protein, dry matter). In such a combination, soybean meal can replace up to 25% of the fishmeal as a protein source. Blood meal exceeding 6%, groundnut cake beyond 10%, soy- bean meal above 20%, and wheat bran beyond 10% retarded fish growth. High mortality was gen- erally observed when these levels were exceeded, even in only one of the protein sources.
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ItemCulture Of The Australian Red-Claw Crayfish (Cherax Quadricarinatus) In Israel Crayfish Incorporation Into Intensive Tilapia Production Units(Israeli Journal of Aquaculture - BAMIGDEH, 2001)This study tested the suitability of the Australian red-claw crayfish Cherax quadricarinatus for rear- ing in an intensive culture system as a supplement to Oreochromis niloticus. Fish were grown in twelve 5.5 m3 tanks at high density (33/m3) for 133 days, alone or with crayfish at two stocking den- sities (10/m2 and 20/m2) with added shelters or with crayfish at the lower density (10/m2) without shelters. Tilapia survival ranged 90.3-95.0% with no significant differences among treatments. The growth rate of the tilapia raised with crayfish (2.05 g/day) was significantly higher than that of tilapia grown alone (1.88 g/day) probably because the fish were feeding on part of the crayfish pellets. Among treatments, there were no significant differences in fish yield. Crayfish survival was extremely low in the ‘no shelter’ treatment (2.9±2.7%) but reasonable (approximately 60%) when raised with shelters. The growth rate of the crayfish raised with shelters was significantly higher at the lower density (0.21 g/day) than at the higher density (0.18 g/day). Further research is needed on rearing tilapia and crayfish to market size in intensive systems, to establish the economic prof- itability of this culture strategy.
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ItemFull-Sib Mating Can Reduce Deleterious Effects Associated With Residual Sperm Inheritance In Gynogenotes(Israeli Journal of Aquaculture - BAMIGDEH, 2001)Fertilization of Oreochromis aureus eggs with UV-irradiated sperm from the closely related species O. niloticus, followed by diploidy restoration, produced offspring with lower embryo viability and higher skeletal deformation rates than siblings generated with sperm from a genetically distant species (Tilapia zillii). Results showed that: (a) deleterious effects due to O. niloticus sperm accu- mulate in gynogenetic fish over generations; (b) such effects are eliminated when using T. zillii sperm to fertilize eggs from gynogenetic mothers produced by full-sib matings. These results sug- gest that: (a) deleterious effects are associated with residual male DNA fragments which may be passed on to descendent offspring; (b) such fragments are significantly purged following full-sib mating. These findings suggest that biparental reproduction may play an important role in the con- trol of genome integrality by purging supernumerary chromosome fragments.
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ItemForecasted Supply And Demand For Comestible Fish In Israel - 2001-2005(Israeli Journal of Aquaculture - BAMIGDEH, 2001)Between 1994 and 1998, the total inland (freshwater) aquaculture production in Israel rose 6.5% from 15,681 to 16,700 tons. This positive trend, however, reversed in 1999, as a consequence of an outburst of a new viral disease that killed 1500 tons of common carp and large quantities of orna- mental cyprinids. During the same period (1994-9), marine aquaculture production grew 688% from 350 to 2408 tons. In the future, this trend may be inhibited by environmental regulations. Because of the expected demographic growth, the local demand for edible fish will grow 16.5% from 64,910 tons in 1999 to 75,600 tons by 2005. To meet this demand, the combined supply from imports and local production will have to grow at 2.58% per year. Anything short of that will boost prices and possibly deter consumers from buying fish. In spite of industry efforts, production of local fisheries and aquaculture has not exceeded 6000 and 19,000 tons, respectively. Fish imports aver- age 63.7% of the national consumption. Most of the imports originate in marine fisheries. According to the FAO, supply from global fisheries is expected to lag behind global demand, causing prices to rise. Long-term efforts by Israeli farmers and the government to adopt aquafarms have enabled inland aquaculture to cope with increasing restrictions on water use for agriculture and maintain a slight growth in production during the last decade. If financially backed by the government, aqua-farms are expected to develop intensive closed water culture systems that will eventually enhance production in spite of the scarcity of water.