IJA Volume 55, Issue 4, 2003
Permanent URI for this collection
1 - 6 of 6
ItemInfluence Of Brackish Water On Survival And Growth Of The Juvenile White Grouper, Epinephelus Aeveus(Israeli Journal of Aquaculture - BAMIGDEH, 2003)The natural habitat of the white grouper, Epinephelus aeneus, is the Mediterranean Sea, which has a salinity of approximately 35 ppt. As fish species vary in their tolerance of environmental conditions, potential production in specific conditions must be determined empirically. The growth, survival and cortisol level of 1.7 g grouper juveniles grown in diluted sea water (4 ppt) or brackish water (4 ppt) from the Tsofar well in the Arava (southeastern Negev, Israel) was com- pared to the growth of similar fish in sea water (43 ppt). Survival in all treatments was 100%. During the first ten days, the fish grown in brackish water grew significantly less (p<0.01) than the fish grown in full-strength or diluted sea water. There were no significant differences between the treatments during the second growth period or in the final weight (approximately 9 g). Total cortisol concentrations ranged 2.7-4.5 ng/l and did not significantly differ between treatments. Results indicate that the white grouper can flourish in water with salinity as low as 4 ppt and that there are no detrimental chemical factors in the brackish water from the Tsofar well.
ItemMarine Recirculating Systems In Israel-Performance, Production Cost Analysis And Rationale For Desert Conditions(Israeli Journal of Aquaculture - BAMIGDEH, 2003)A semi-commercial 100 m3 marine recirculating system (RAS) was designed, based on the results of a 5 m3 experimental system. The system was stocked with gilthead seabream (Sparus aurata). After 200 days, the fish in the semi-commercial system had a similar weight (about 330 g) and density (78 kg/m3) and identical survival (99%) and FCR (1.8) as similar fish grown in a flow-through system (FAS). Annual production in the RAS was calculated as 90 kg/m3. Seawater consumption was 3.5-4 m3 per kg fish produced, resulting in an average water exchange rate of 80% of the system volume per day. While this is relatively high compared to freshwater RAS, the marine RAS required only 10% of the sea water consumed in an FAS. Since sea water is an inexpensive input, water consumption was a minor component of the total production costs in the RAS (approximately 6%). The economical analysis for a theoretical 500 ton/y farm showed that the main capital investment components would be the rearing volume (fish tanks) and the biofiltration unit, representing over 60% of the total investment. The highest production costs would be feed, fingerlings and return on the investment, in that order, representing over 50% of the production costs. CO2 stripping may limit further intensification because the limited surface area of the tank limits the number of paddlewheels that can be used. Also, the DO/TAN ratio may be a factor limiting achievement of a higher nitrification rate and reduction of the biofilter size. Based on the results of this study, a 100 ton/y pilot plant is currently being designed as a model farm.
ItemDefining Energy And Protein Requirements Of Gilthead Seabream (Sparus Aurata) To Optimize Feeds And Feeding Regimes(Israeli Journal of Aquaculture - BAMIGDEH, 2003)Energy and protein requirements of growing fish can be quantified as the sum of the amounts of energy and protein retained as growth plus the amounts simultaneously lost from the body. The requirement for dietary gross energy and protein can be calculated using the respective effi- ciencies of utilization. Growth of gilthead seabream as a function of body weight and tempera- ture was predicted by the equation: y = 0.024 x BW0.514 x exp0.060T (where y = daily weight gain in g/fish, BW = body weight in g and T = temperature in °C). The gain was determined in fish ranging 1-470 g. The energy content of the fish depended on fish weight and rose from 4.7 to 11.0 kJ/g body mass as the fish grew whereas the protein content was constant at 176 mg/g regardless of fish weight. The efficiencies of utilization of digestible energy (DE) and digestible protein (DP) for maintenance and growth were determined by feeding the fish at increasing feed- ing levels from zero to the maximum voluntary feed intake. The daily requirement of DE for main- tenance was dependent on temperature and determined as (16.6kJ x exp0.055T)/BW in kg0.82. The maintenance requirement for DP was independent of temperature and equaled 0.62g/ BW in kg0.70. The relationship between DE intake and energy gain was linear, constant at kDEg = 0.67 and independent of feed intake and temperature. Efficiency of protein utilization for growth var- ied between 0.33 and 0.80 depending on the DP/DE ratio in the diet. The optimal protein uti- lization for protein deposition was estimated at kDPg = 0.47. Using these values allows optimiza- tion of feeding for seabream culture.
ItemKey Factors Influencing Juvenile Quality In Mariculture: A Review(Israeli Journal of Aquaculture - BAMIGDEH, 2003)Environmental (temperature, salinity) and nutritional (DHA, EPA, ArA, vitamin A, phospholipids, iodine) factors during larvae rearing largely dictate the successful transformation of larvae to juveniles during metamorphosis which, in turn, determines juvenile quality. Studies on Atlantic halibut, turbot and Japanese flounder report higher metamorphic success, in terms of pigmen- tation, eye migration and general development, when copepods, rather than enriched Artemia, were fed to larvae. Copepods have higher levels of vitamin A, which is required for the synthe- sis of rhodopsin in the retina, a critical visual pigment in the rods necessary for vision at low light intensities. Deficient rhodopsin affects neural transmission from the retina via the central nervous system that triggers pituitary production of melanophore stimulating hormone leading to reduced melanin synthesis and pigmentation deficiency. DHA, an abundant PUFA in copepods, is also vital to vision as it provides the membrane fluidity necessary for rhodopsin to function when stim- ulated by light. The essential fatty acids EPA and ArA are more involved in eicosanoid synthe- sis. These highly potent metabolites are thought to regulate the mechanisms involved in the release of melanophore stimulating hormone and pigmentation. Thyroid hormones play a major role in regulating many developmental processes that occur during metamorphosis. Immersing different age marine fish larvae into various concentrations of thyroid hormone has been shown to synchronize and shorten the duration of metamorphosis in a dose dependent manner in species such as grouper. However, the effect of this immersion on survival varied with the type of thyroid hormone, dose and timing of application. In some species, such as the European seabass (Dicentrarchus labrax), females grow up to 40% faster than males. However, when this species is intensively cultured, masculinization can result in a 70-90% male population. A num- ber of studies have shown that manipulating temperature and salinity during larviculture can result in higher quality juveniles, i.e., a higher percent of faster growing females.
ItemParental Effects On Sex Ratios In Progeny Of The European Sea Bass (Dicentrarchus Labrax)(Israeli Journal of Aquaculture - BAMIGDEH, 2003)In European sea bass (Dicentrarchus labrax), females grow 20-50% faster than males. Therefore, they are more in demand than males for commercial farming, generating much inter- est in the development of female monosex populations. Whereas most current research focus- es on the influence of temperature on sex determination, the present experiments aimed at studying parental effects on sex ratios in progeny. The study analyzed progeny resulting from a diallel crossing (2 x 2 type or a complete bi-factorial mating design), reflecting both maternal and paternal genetic relatedness among progeny. The proportion of females varied significantly among families (20.7-68.2%). There were significant maternal and paternal effects on the pro- portion of females among the progeny. The effect of the parental interaction on the sex ratio in the progeny was also significant. Parents had a significant effect on total length and body weight. Sexual growth dimorphism, in favor of females, was evident in all the full-sib families and varied significantly between families. Among offspring at 9-9.5 months (68.9±23.7 g), females were 26.6% heavier than males. It is concluded that in addition to temperature manipulation in sea bass, as proposed in earlier studies, selection of parents will probably result in an improved ratio of female to male progeny.
ItemMariculture in Israel(Israeli Journal of Aquaculture - BAMIGDEH, 2003)Israel is a long narrow country occupying 180 km of the eastern shore of the Mediterranean and 12 km of the shore of the Gulf of Aqaba/Eilat, Red Sea. More than half of the country, the southern half, is desert and receives less than 200 mm of rain annually. Therefore, the country suffers from a chronic shortage of fresh water and it is not surprising that governmental agencies encourage the development of food production systems using sea water. Governmental activities began in the early 1970s with the establish- ment of the National Center for Mariculture (NCM) in Eilat, as part of the Israel Oceanographic and Limnological Research Institution (IOLR).