The aims of the investigations were to estimate the biomass and the production of the macrozoobenthos and to know their season dynamics. Investigations were supported by Fishery's Foundation. Sediment chemical analysis showed that the macrozoobenthos biomass was determined by the quantity of the phosporus. Chironomid larvae formed the 70-90 per cent of benthos biomass in Keszthely basin.

Commercial fish landing at Abu Qir and Alanfoushy markets was the source of Siganus rivulatus and Siganus luridus sampled for food and feeding habits analysis. Food indices and food content were studies in stomach analyses of 1485 fishes

Groups of 0+ Atlantic salmon (Salmo salar) smolts were transferred to duplicate seawater tanks, and subjected to five different ration levels, 0% (starved), 25%, 50%, 75% or 100% (full fed). Waste feed was collected after each meal. After six weeks all groups were re-fed in excess. During the trial period body weight and length increased significantly in the 50, 75 and 100% groups, while no significant changes in body weight were observed in the 0% and 25% groups. A significant decrease in SGR was observed in the 0 and 25% groups during the first month in sea water. After re-feeding, SGR increased in all groups. All groups, except the previously starved group, showed peak SGR between weeks 6-8 and 8-12. Food restriction at 0% and 25% of full ration for a period of six weeks resulted in significant osmotic disturbances. After six weeks in sea water, plasma Cl⁻ levels were higher in the 0% group than in the other groups. Branchial Na⁺,K⁺-ATPase activity increased in all groups following exposure to seawater. Re-feeding caused a transient increase in branchial Na⁺,K⁺-ATPase activity after two weeks in the previously starved group, with a concurrent reduction in plasma Cl⁻ levels. Previous exposure to different ration levels significantly influenced growth rate and mean body size. Compensatory growth and partial size compensation was seen in the 0, 25 and 50% feed deprivation groups, whereas full size compensation was found in the 75% group.

When fed once daily with wet squid, turbot (30-50 g) accustomed to dry pellets require many days to increase intake to meet their feed requirement (approximately equal to 10 mg dry matter g(-1) bw meal(-1)). Adaptation takes 1-2 days if several daily feedings are given. With dried squid, they ingest about 20% of the wet squid bulk because the stomach contents expand when moisturised. In contrast, turbot eat enough wet squid to fill most of the available stomach volume (approximately equal to 7.6 mL 100 g(-1) bw). When presented in gelatine capsules, food water content is masked and does not affect the volume ingested. Moistening the contents shortens the delay before gastric emptying starts to one-third (0.6 h) compared with dry food (1.9 h). Daily dry-matter intake increased when dry contents were moistened but only if two or more meals were offered per day. Turbot adapt their digestion to supply water for dry diets but this may add extra metabolic costs. When offered 20 mg dry matter g bw(-1) day(-1), divided into four equal meals, turbot grew faster and more efficiently with moist than with dry squid. Protein, energy and dry-matter digestibilities were also enhanced. The increased daily protein absorption did not increase ammonia release, indicating that the extra protein was used for somatic growth.

Fish occurring in the outlets of water basins reduce the abundance of zooplankton. The study was performed at the outlet sections of the lake and waste stabilization pond of a sewage treatment plant. The aim of the study was to determine which zooplankton is chosen more often by the roach (<i>Rutilus rutilus</i>), those drifting from the waste stabilization pond or from the lake. The zooplankton from the pond was dominated by <i>Daphnia pulex</i> while zooplankton from the lake was dominated by small planktonic rotifers. We observed that the larger the plankter-victim&#8217;s size, the faster the reduction of its number. The fish were more likely to feed on zooplankton drifting from the waste stabilization pond than from the lake. It was influenced by <i>D. pulex</i> individuals, attractive for fish due to their largest body size among the analyzed zooplankton. The significance of riverine zooplankton in the downstream food web may render this data even more important.

An experiment were conducted to evaluate The effect of feeding frequencies and stocking size on growth and feed conversion ratio (FCR) of rainbow trout (O. mykiss) in brackish water for 102 days. Three stocking sizes (10, 25 and 40 g/fish) of rainbow trout and three feeding frequencies (feeding fish twice, three times and four times per day) were examined as the same time. Fish were fed at a restricted feeding program according to the rainbow trout standard table in the definite times during the light period. The results showed that in the group with 10 g initial weight increasing the feeding frequency, some growth factors like final weight, daily growth, and weight gain. But the other factors such as food conversion rate (FCR) and specific growth rate (SGR) decrease. It means in this group (10 g) two times feeding per day is not enough for an acceptable growth rate. In the two other groups with (initial weight 25 and 40 g) although by increasing the feeding frequency, some growth factors a little increase but these differences in 95% level (p،ـ0.05) are not significant. Therefore in rainbow trout culture with initial weight at least 25 g two times feeding per day was enough. The results of carcasses analysis of fish, showed that by increasing the feeding frequency there were no significantly difference at 95% level between the body compositions in all of treatments. With connivance of feeding frequencies, the best FCR was in the group with 10 g initial body weight and there was not any significant difference in SGR. So according to the results, it suggests that fish should be stocked with 10 g initial body weight.