Ammonia dynamics in relation to hatching in Atlantic halibut (Hippoglossus hippoglossus L.)

Total ammonia content (T_Amm) and excretion (J_Amm), and ionic content (K⁺, Na⁺, Cl_-) have been studied in embryos and yolk-sac larvae of Atlantic halibut (Hippoglossus hippoglossus L.) maintained in darkness (6 °C and 34% S) or in light (light-arrested, nonon-hatching embryos). The T_Amm of the eggs increased from 250-300 nmol ind^-1 during the first 5-10 days post fertilization (dPF) to 400-500 nmol ind^-1 at the time of natural hatching in darkness. T_Amm did not start to decrease before 2-5 days after hatch, and yolk-sac larvae had a higher T_Amm compared to the light-arrested embryos of the same age and batch. J_Amm increased exponentially rom about 0.05 nmol ind^-1 h^-1 at 10 dPF to about 3 nmol ind^-1 h^-1 at hatch. Embryos undergoing hatching showed a significantly higher J_Amm than non-hatching, light-arrested embryos of the same age. The content of K+ in distilled water rinsed eggs declined from about 0.85 µmol ind^-1 at 2-4 dPF to about 0.15 µmol ind^-1 at hatch, while that of Cl^- remained constant at about t 0.85 µmol in^-1, and that of Na⁺ increased slowly from 0.10 to 0.20 µmol ind^-1 . Based on the measured ions, there was an anionic deficit in the egg, especially during the first week of development. When exposed to increased ambient total ammonia (0-27 mM NH4Cl), no mortality occurred, and no significant increase was found in the T_Amm of the Atlantic halibut egg before 9.2 dPF despite an estimated large inward diffusion gradient for the un-ionized ammonia species (NH₃). The delayed release of T_Amm comp ared to embryos and yolk-sac larvae of other marine teleosts, may relate to the deep-water spawning of the Atlantic halibut, and the buoyancy regulation of the yolk-sac larvae.     

Triploid Induction in Atlantic Cod (Gadus morhua L.) by the Use of Different Pressure Levels

Different levels of pressure were investigated to see if it was possible to induce triploidy at a lower pressure than previously used (600 bar) for Atlantic cod (Gadus morhua). Newly fertilized eggs were exposed to different levels of pressure: 400, 500, and 600 bar, and one control group (no pressure). Induction of triploidy occurred at each pressure level used in this experiment. Mean weight and length at the termination of the trial period was significantly lower, in the 400 bar group, compared to the other treatment groups. Microsatellite loci analysis revealed over 90% triploid outcome in each experimental group. Lower incidence of deformities was seen in the 400 bar group compared to the 500 and 600 bar groups. Overall this study demonstrated successful triploid induction at both low (400 bar) and medium (500 bar) pressures.     

Water balance in developing eggs of the codGadus morhua L.

Measurements of yolk osmolality from the embryo of codGadus morhua L. revealed significant variations in the hyposmolality during the embryonic development. The embryo proved to have an extremely low water permeability, protecting it from dehydration in the hyperosmotic seawater. The effect of temperature on the water permeability is high, expressed by an exceptionally high activation energy for water transfer. The agreement between embryonic volume decrease and diffusion permeability during the first 8–10 days after fertilization indicates that no water uptake mechanism is present at this time, thus leaving the embryo fully dependent on internal water stores. The cod egg is buoyant in seawater throughout development. The mechanism for providing hydrostatic lift is the large volume of diluted tissue water located in the yolk and subdermal spaces.     

Effect of feed composition and feeding frequency on growth, feed utilization and nutrient retention in juvenile Atlantic cod, Gadus morhua L.

Juvenile Atlantic cod (Gadus morhua) were fed extruded feeds formulated to contain 360–660 g kg^?1 protein, 80–280 g kg^?1 lipid and 80–180 g kg^?1 starch at feeding frequencies of either once per day or every second day to satiation. The trial was conducted at 8 °C and lasted for 28 weeks during which fish were weighed five times at regular intervals. Sampling for proximate analysis was performed at the start, after 12 weeks and at the end of the trial. Fish grew from an average weight of 192 g to between 750 and 866 g, with growth being negatively affected by low dietary protein concentration. High dietary starch concentrations had some negative effects on growth, whereas changes in dietary fat concentration had no significant effect on growth. Liver indices (at the end of the experiment) varied between 80 and 170 g kg^?1, and there was a negative correlation between the ratio of protein to fat and liver index. Feed conversion ratio (FCR) ranged between 0.74 and 0.88, and feed utilization improved with increasing concentrations of dietary protein and fat. Increasing dietary starch concentrations resulted in poorer feed utilization. To achieve good growth and protein retention, and avoid excessive liver size in juvenile cod, feeds should contain 500–600 g kg^?1 crude protein, 130–200 g kg^?1 lipid and <150 g kg^?1 starch.     

Effects of Dietary Vitamin C on Maturation and Egg Quality of Cod Gadus morhua L.

The effects of dietary vitamin C on maturation and egg quality of cod Gadus morhua L. have been investigated. The broodstock groups were fed three different levels of vitamin C mixed into a commercial dry pellet. The experimental feeding started three months prior to the spawning season. Naturally spawned eggs were collected and analyzed with regard to viability, biochemical composition and physical characteristics. Differences in free amino acid profile, egg strength and neutral buoyancy were found, whereas no effects on vital parameters, such as fertilization rate and survival rate, were detected.     

Effect of dietary carbohydrate on gonadal development in broodstock cod, Gadus morhua L.

Diets with increasing levels of potato and maize starch were fed to duplicate groups of maturing cod, Gadus morhuaL., from June 1991 to January 1992.The level of starch in the diet did not influence feed conversion factors, broodfish growth or gonadal development. Low levels of fillet glycogen were measured at all samplings, without variations according to dietary starch, or to developmental stage of the brood fish. During the reproductive phase no decreases were measured in relative liver size or liver protein, lipid or glycogen, indicating no net use of stored energy from the liver to build up gonads as long as the fish was offered feed. The variations in dietary starch vs. protein did not alter the composition of gonad dry matter, protein, lipid or glycogen levels. However, dry matter and protein levels increased during maturation in all groups. Plasma glucose levels were within normal ranges in all dietary groups at all sampling times, indicating no negative effects of high levels of dietary starch in brood fish, as also confirmed by stable and normal haematocrit, red blood cell count, and mean cell volume in blood. Haemoglobin, mean cell haematocrit and mean cell haemoglobin concentration decreased during the reproductive phase. Serum haemolytic complement activity did not vary between dietary treatments. Glycogen, dry matter, protein and lipid levels in eggs did not vary between dietary treatments of brood fish. Very low levels of glycogen were measured, suggesting that this energy reserve was of minor importance. Dry matter and lipid levels were quite stable in relation to egg developmental stage: protein levels decreased from day 0 until hatching.     

Drinking activity of the newly hatched larvae of codGadus morhua L.

The drinking rate of cod larvae 1–7 days post hatching was measured from the uptake of³H-labelled dextran (MW = 70000) admixed in the incubation seawater (34 ppt 5°C). The drinking rate increased gradually from 0.15% to 0.59% of the larval body weight on day 1 and day 7 respectively. This increase in drinking rate correlated with an observed decrease in the volume of the yolk sac and its water store. Autoradiographs showed the labelled dextran to be confined to the intestine. Electron micrographs showed an open mouth communicating with the oesophagus and the intestine in cod larvae at the time of hatching. Chloride cells were present on the opercular folds but not on the vestigial, developing gills. The data indicate that the water acquisition mechanism of larval cod is similar to that of adult marine fish.     

Atlantic halibut, Hippoglossus hippoglossus L., larvae cultivation literature, including a bibliography

The first attempts to rear Atlantic halibut, Hippoglossus hippoglossus L., larvae were carried out in Norway in the period from 1974 to 1980, when ripe adult specimens of Atlantic halibut were net-caught, and stripped for eggs and milt. Both incubation of yolk-sac larvae and first-feeding were carried out in large submerged plastic bags and the larval food consisted of natural zooplankton collected from surrounding lagoon water. This semi-extensive production method was further developed and led to the establishment of several commercial production trials by the end of the 1980s. During recent years, research has been focused on intensive methods for first-feeding and the combined effort of several research institutes has resulted in a reliable production method. During the late 1980s and early 1990s, the main research activity was focused on the biology of and rearing techniques for eggs and yolk-sac larvae. These techniques provided satisfactory yields for several years. However, during the past few years, a certain decrease in survival through the yolk-sac stage has been experienced at several hatcheries. Since the early 1990s, the first-feeding period has represented the bottleneck in the development of a reliable rearing method. The main effort has been concentrated on system configuration and on improving live prey quality. In the future, new feeding strategies including further improvement of live prey (i.e. Artemia), the use of copepods and early weaning onto a formulated diets should be emphasized. Further research on hygiene and technological improvements is needed to increase growth and survival through metamorphosis.     

A tank design for first feeding of Atlantic halibut, Hippoglossus hippoglossus L., larvae

An intensive method of juvenile Atlantic halibut, Hippoglossus hippoglossus (L.), production has been under development over the last decade because of the problems associated with the extensive method. The lack of initiation of feeding behaviour has been the main obstacle for successful indoor rearing under artificial light and feeding conditions. In the present paper, an intensive method for the first feeding of halibut larvae is described and verified by practical feeding trials. The method involves circular 1.5-m³ indoor tanks with a peripheral ring-shaped cover, the use of continuous light, UV-A radiation during the first 24 h, central up-welling of water made by aeration and the use of microalgae in the rearing water. The single most important factor in such systems is to maintain a current pattern which allows the larvae to orientate and position themselves to face the water current for easy capture of prey.     

Genome of the host-cell transforming parasite Theileria annulata compared with T. parva

Theileria annulata and T. parva are closely related protozoan parasites that cause lymphoproliferative diseases of cattle. We sequenced the genome of T. annulata and compared it with that of T. parva to understand the mechanisms underlying transformation and tropism. Despite high conservation of gene sequences and synteny, the analysis reveals unequally expanded gene families and species-specific genes. We also identify divergent families of putative secreted polypeptides that may reduce immune recognition, candidate regulators of host-cell transformation, and a Theileria-specific protein domain [frequently associated in Theileria (FAINT)] present in a large number of secreted proteins.