Maximum ration of four algal diets for the oyster Crassostrea virginica Gmelin

The rate of removal of four species of alga from suspension by the oyster Crassostrea virginica was determined. The number of cells removed per hour depended upon the size of algal cells, but the total dry weight of algal material removed over 24 h was independent of size. Filtration rate was dependent upon the density of the algal suspension, and large quantities of pseudofeces were produced by oysters filtering algae from suspensions denser than 10 μg/ml.Oysters showed periods of high filtering activity and periods of relative quiescence during experimental trials of 24 h duration. Based on the periodic filtering activity of the oysters, a discontinuous feeding regime is proposed along with an equation predicting the maximum daily ration of oysters of various sizes.     

Comparative effects of diets consisting of one or two algal species upon assimilation efficiencies and growth of juvenile oysters, Crassostrea virginica (Gmelin)

Juvenile oysters, Crassostrea virginica, were fed one of six diets consisting of three species of algae fed singly or in two-species combinations. Dietary components were Isochrysis galbana (Diet I), Platymonas suecica (Diet P), and Thalassiosira pseudonana (Diet T). High (Diet TI), intermediate (Diets T, I, PT, PI), and low (Diet P) growth responses were observed. Intermediate and low growth responses were explained in terms of differing levels of ingestion and assimilation. The high growth response with Diet TI was not explained by measured values of ingestion and assimilation.     

Growth of 0-group turbot (Scophthalmus maximus L. 1758) fed on artificial diets

Group-0 turbot Scophthalmus maximus L. were fed on artificial diets for 13 months, at 15° C. Partially defined diets containing about 40% protein were used and fish were fed once per day with moist pellets.The mean weight of the fish, at the beginning of the experiment, was 3.5 g. During the first 6 months, a fish gained 15 g weight on average, and 40 g in the following 6 months. The final mean weight was 62 g, and the final mean total length, 15.3 cm. The daily growth rate was 0.7% and the protein efficiency ratio (P.E.R.) ranged between 1.4 and 2.1.For fish fed on natural food at 15° C, the results were similar for the first 9 months. Subsequently, these fish grew faster than those fed artificial diets.     

Growth and economic performance of Nile tilapia (Oreochromis niloticus L.) fed on two formulated diets and two locally available feeds in fertilized ponds

Lack of suitable diets for semi‐intensive production of Oreochromis niloticus in Kenya has necessitated use of expensive diets designed for intensive production. To address this problem, two isonitrogenous (24% protein) diets were formulated and evaluated for production of O. niloticus in fertilized ponds. One diet contained vitamins and minerals premix (CV) while the other had no premix (CW). Growth of fish fed on the formulated feeds was compared with groups of fish fed on commercial pig pellets (PP) and wheat bran (WB). There were significant differences in mean weights, growth rates and feed conversion ratios between the formulated and the other diets. No significant differences in these parameters were observed between CV and CW and also between PP and WB. Fish that fed on the formulated feeds produced significantly lower number of juveniles than those fed on PP and WB. Fish fed on WB gave the best economic returns while those on PP had the least returns. Present results suggest that vitamins and minerals premix may not be necessary in diets for semi‐intensive production of O. niloticus. Present results showed that the formulated feeds produced higher yields than PP and WB, but WB had the best economic returns among the test diets.     

Growth, feed conversion and chemical composition of Atlantic salmon (Salmo salar L.) and Atlantic halibut (Hippoglossus hippoglossus L.) fed diets supplemented with krill or amphipods

The effects of partial replacement of fish meal (FM) with meal made from northern krill (Thysanoessa inermis), Antarctic krill (Euphausia superba) or Arctic amphipod (Themsto libellula) as protein source in the diets for Atlantic salmon (Salmo salar L.) and Atlantic halibut (Hippoglossus hippoglossus L.) on growth, feed conversion, macro‐nutrient utilization, muscle chemical composition and fish welfare were studied. Six experimental diets were prepared using a low‐temperature FM diet as control. The other diets included northern krill where 20, 40 or 60% of the dietary FM protein was replaced with protein from northern krill, and two diets where the FM protein was replaced with protein from Antarctic krill or Arctic amphipod at 40% protein replacement level. All diets were iso‐nitrogenous and iso‐caloric. Atlantic salmon grew from 410 g to approximately 1500 g during the 160 day experiment, and Atlantic halibut grew from 345 g to 500–600 g during the 150 day experiment. Inclusion of krill in the diets enhanced specific growth rate in salmon, especially during the first 100 days (P < 0.01), and in a dose–response manner in halibut for over the 150 day feeding period (P < 0.05). Feed conversion ratio did not differ between dietary treatments, and no difference was found in dry matter digestibility, protein digestibility and fish muscle composition. Good growth rates, blood parameters within normal ranges and low mortalities in all experimental treatments indicted that fish health was not affected either Atlantic salmon or Atlantic halibut fed the various zooplankton diets.     

Hyper dense vertebrae and mineral content in Atlantic salmon(Salmo salar L.) fed diets with graded levels of phytic acid

The effects of graded levels of phytic acid on skeletal development and mineral deposition were investigated in an 80 day feeding trial with Atlantic salmon (Salmo salar L.) parr. The level of phytic acid had no significant effect on the phosphorus (P) content of either whole body or vertebral column of Atlantic salmon. Negative effects of high phytic acid levels were, however, found on whole body concentration of calcium (Ca), magnesium (Mg), and in the Ca:P ratio, and in the vertebral column concentration of zinc (Zn). A novel type of vertebral pathology was observed, hyper dense (HD) vertebrae. The HD vertebrae appeared denser on radiographic images, and they consisted of a denser trabecular network than the surrounding vertebrae. The number of fish with HD vertebrae increased from initially 16% to 45-60%, with a tendency of more fish with HD vertebrae with increasing dietary phytic acid content. The HD vertebrae are described and illustrated with radiographic images, whole mount staining, and histology.     

Growth performance of the early life stages of broad‐nosed pipefish,Syngnathus typhle (L.) fed different live or frozen diets

This work tested the effect of using different live and frozen feed on the growth performance of Syngnathus typhle. It was divided into two experiments. In Experiment I Artemia and Atlantic ditch shrimp (Palaemonetes varians) larvae were used as live diets, whilst in Experiment II frozen mysids Mesopodopsis slabberi and frozen P. varians were used. At the end of the first experiment juvenile pipefish grew significantly more when fed P. varians (P < 0.05) with an overall Weight Gain (WG) of 914.8 ± 79.3% bw day^?1, compared to Artemia fed fish (WG = 683.2 ± 14.7%). Both mean Specific Growth Rate (SGR) and survival were similar between dietary treatments and did not vary significantly (P > 0.05). In Experiment II juveniles were weaned with frozen diets but no significant differences were found between the two tested diets in all parameters tested. Final WG was 516.5 ± 63.3% and 566 ± 17.6%, and Feed Conversion Ratio (FCR) was 30 ± 1.5% and 28.2 ± 1.2% for animals fed P. varians and M. slabberi respectively. Results indicate that P. varians is an adequate diet to use during initial stages of the S. typhle life cycle and should be considered as a frozen diet for subsequent life stages of this species as an alternative to currently known natural diets.     

Growth of three salmonid species in mono and double culture (Salmo salar L., S. trutta L. and S. gairdneri Rich.)

Juvenile Atlantic salmon, sea trout and rainbow trout were used in an experiment in which two species in each tank were compared with controls of each species separately. Specific growth rate was best in the experimental groups where the two species were reared together. The theory was developed that social facilitation or moderate interaction could cause the better growht. No starvation as a result of competition was discovered in any group.     

Growth variation and fin damage in Atlantic cod (Gadus morhua L.) fed at graded levels of feed restriction

Atlantic cod (initial weight 55, 250 and 450 g) were deprived of feed for 1 month or fed one of two diets differing in crude protein and lipid levels at rations corresponding to about 25, 50, 75 or 130% of group satiation for two months. The fish were individually weighed at the start, mid and end of the experiment and growth variation and fin damage were registered. The fin damage patterns differed between size groups; 55 g cod had most wounds on the dorsal fins whereas the pectoral fins were the most damaged in the 250 g fish. The incidence of damage in these groups was high and increased significantly when feeding was restricted. In the 450 g cod there was little fin damage and the incidence did not seem to depend on diet treatment.In the 55 and 250 g cod groups, fast growing fish had lower incidence of fin damage than fish that grew slowly, suggesting that the fish that received most aggression were prevented from feeding. However, a similar trend was registered in non-fed fish, showing that the recipients of aggression also suffered other disadvantages.The variation in individual growth rates increased when feeding was restricted and the distribution was differently skewed depending on feeding level. The data provide evidence that competition is an important factor limiting growth of individual cod held in groups in culture.     

Seasonal variations in muscle growth dynamics and selected quality attributes in Atlantic halibut (Hippoglossus hippoglossus L.) fed dietary lipids containing soybean and/or herring oil under different rearing regimes

Atlantic halibut (Hippoglossus hippoglossus), 1630 ± 510 g at the start of the experiment were reared in tanks for 1 year and subjected to three different environmental regimes; Continuous light and Constant temperature (CC), Natural light and Constant temperature (NC) or Natural light and Ambient temperature (NA). Two diets were fed, where 50% of the dietary lipids were either herring oil or soybean oil supplemented. The fish were sampled in May, August and November the first year, and February and May the following year. The CC groups grew better than the NC and NA groups from May to November, and as a result had a significantly (p < 0.05) higher weight by the end of the experiment. This difference did however not affect muscle fibre size distribution, or the chosen muscle quality attributes texture, fat content, water or fat loss of the fillet. These quality attributes were influenced by season and body weight, whereas diet had no significant effect. The NA group had lower fat content of the fillet than the other environmental regimes in August, November and May_end, and fat content increased with increasing fish weight. Water and fat losses were lowest in November and February. The diet influenced the fatty acid profile of the musculature; the triacylglycerol fraction reflecting the dietary treatment while the polar fraction was less influenced by diet. The hardness of the fillet was not influenced by the environmental regimes, but by season, and hardness was at its lowest in August, and increased towards the following spring. The muscle fibre distribution varied only with season, and neither treatment nor diet had any effect on the muscle growth dynamics. Recruitment of new fibres seemed mainly to occur during winter, signified by maximum occurrence of fibres < 500 μm² by the end of the experiment in May.