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This study describes the muscle fibre type distribution and the swimming activity in early stages of Clarias gariepinus (Burchell). It also describes the influence of different diets on muscle fibre numbers and muscle fibre diameters of Clarias larvae. Yolk-sac larvae of Clarias have a superficial monolayer of red muscle fibres that surrounds inner “white” muscle. At about 11 mm length (larvae fed for 3 days on Artemia), an adult­like fibre type distribution begins to appear. One day after hatching, the larvae (about 5 mm total length) show nearly continuous stationary activity interrupted by slow swimming (velocity 2.4 ± 0 .9 body length per second (BL s-1)). This activity is probably powered by the superficial red fibres. Stimulation of the larvae results in burst-swimming with an initial velocity of at least 17 BL s-1, which is probably powered by the inner white fibres. After yolk-sac absorption the time spent in stationary activity and swimming decreases. From the start of feeding, a group of larvae was fed with Artemia and another group with dry food. Larvae fed for 3 d on Artemia and larvae fed for 5 d on dry food have similar length, similar white muscle fibre sizes, and similar white muscle fibre numbers. This indicates that muscle develop­ment is related to the length of the larvae, rather than to age. Article from Marine Science Symposia Vol. 201 - "Mass rearing of juvenile fish". Symposium held in Bergen, 21-23 June 1993. To access the remaining articles please click on the keyword "MSS Vol. 201".

Methods and concepts developed in research on the energy balance of husbandry animals (including fish) are used in studies on nutrient and energy requirements and feed evaluation. Because of methodological difficulties, in fish such studies were restricted to juvenile and adult animals. Data on energy resource partitioning in larval fish are scarce. Eleuthero-embryos provide a good model for the study of energy metabolism in the early life stages of fish, since they constitute a simple system without dietary influence. In the present paper, a review of energy resource partitioning in the African catfish ( (Burchell)) is given, based on data of the proximate analysis of growing embryos during the egg and eleuthero-embryonal stage and of starving larvae. Oxygen consumption, carbon dioxide production and ammonia ex­cretion were also measured. Both the proximate analysis data and the respirometry measurements were used to assess the energy substrates during subsequent develop­mental stages. The results are compared with the predictions of a computer simulation model based on the biochemical pathways underlying the energy metabolism. Article from Marine Science Symposia Vol. 201 - "Mass rearing of juvenile fish". Symposium held in Bergen, 21-23 June 1993. To access the remaining articles please click on the keyword "MSS Vol. 201".

Larval growth can be improved through the reduction of energy expenditure, which has been correlated with the rate of protein synthesis and hence to amino acid metabolism. Understanding the dynamics and regulation of the amino acid metab­olism may contribute to the formulation of larval diets. A model was developed to simulate amino acid fluxes in yolk-sac larvae. The model considers the flux of amino acids through three pools: amino acids in the yolk; free amino acids in the body; and protein-bound amino acids in the body. Each pool is subdivided into sub-pools of the individual amino acids. Yolk amino acids are absorbed into the body free pool, a process which is proportional to yolk volume and to the pool of amino acids in the yolk. The body-free pool is used for catabolism and protein synthesis, with the respective rates increasing with both body size and amino acid concentration. Amino acids are released into the free pool as a result of protein breakdown. Protein turnover was estimated during development of yolk-sac larvae. Results suggest that efficiency of protein retention is lower than 50% in yolk-sac larvae. Minimal values for fractional rates of protein synthesis were estimated to be 300% d -1 (Clarias gariepinus) and 30% d -1 (Hippoglossus hippoglossus). Different amino acids provided similar estimates for protein turnover. Article from Marine Science Symposia Vol. 201 - "Mass rearing of juvenile fish". Symposium held in Bergen, 21-23 June 1993. To access the remaining articles please click on the keyword "MSS Vol. 201".

Changes in protein, lipid, and energy contents of developing Clarias gariepinus eggs and larvae are examined. The mean egg weight is 1.3 mg, with an average composition of 79.2% water, 20.7% protein, 5.6% lipid, and 2.1% ash. Hatching occurs at 52 physiological day degrees (PD°) and yolk is completely absorbed at 205 PD°. Exogen­ous feeding starts at 166 PD°, before complete yolk-sac absorption. From fertilization until the sampling point closest to complete yolk absorption ( 195.4 PD°), conversion efficiencies of yolk dry matter, protein, and lipid to body tissue are respectively 73.5%, 74.2%, and 47.4%. In the same period, protein and lipid contribute respectively 1.6 and 1.5 J/ind to the total energy expenditure. Article from Marine Science Symposia Vol. 201 - "Mass rearing of juvenile fish". Symposium held in Bergen, 21-23 June 1993. To access the remaining articles please click on the keyword "MSS Vol. 201".

Polychaetes comprise the benthic meiofauna of the soft-bottom intertidal zone and of shrimp ponds in coastal areas. While polychaetes provide benefits to the shrimp farming industry as (i) natural food in traditional shrimp ponds, (ii) nutrient regenerators through bioturbation and removal of organic waste in the sediment through feeding, and (iii) feed supplement to enhance maturation of shrimp brooders, the conditions present in aquaculture ponds may increase the opportunity for polychaetes to transfer pathogens to shrimp through the food chainThere is growing concern that internationally traded polychaetes, which are fed to shrimp brooders, are potential vectors for the transmission of other shrimp pathogens. The detection of the aetiological agents of two newly emerging diseases of shrimp in polychaetes, Enterocytozoon hepatopenaei (EHP) and Vibrio parahaemolyticusAHPND causing hepatopancreatic microsporidiosis (HPM) and acute hepatopancreatic necrosis disease (AHPND), respectively, suggests that these worms can be a host or/and passive carrier of these pathogens. This review discusses the benefits of polychaetes to shrimp farming, the risk of shrimp pathogen transmission by polychaetes at the pond, hatchery and global level, and calls for closer observation on shrimp pathogens in polychaetes used as shrimp feed.

The effect of two dietary electrolyte balance (dEB, Na K - Cl-) levels on arterial and portal blood oxygen content, blood pH, and acid-base status in pigs was studied during a 9-h period after a meal, using a crossover experimental design. The dEB levels were established by changing the Cl- level in the diets. Four pigs with a mean weight of 45 kg were surgically fitted with catheters in the carotid artery and portal vein. Two dEB levels (-100 and 200 mEq/kg) were evaluated in two periods of 1 wk each. Feed was given at 2.6 times the maintenance requirement for energy in two meals per day. Water was freely available. Blood samples were taken at 0, 0.5, 1, 1.5, 2, 3, 4, 6, and 9 h after feeding. Blood hemoglobin; O2 pressure; O2 saturation; O2 content; pH; PCO2; HCO3-; base excess; and Na , K , and Cl- contents were measured. Oxygen contents in arterial and portal blood were lower (P < 0.008) in the -100 mEq/kg group (5.78 and 4.82 mmol/L respectively) compared to the 200 mEq/kg group (6.18 and 4.99 mmol/L respectively). This was related to the lower hemoglobin content in the blood of animals in the -100 mEq/kg group. Arterial and portal blood pH were lower (P < 0.003) at -100 mEq/kg (7.46 and 7.37) than at 200 mEq/kg (7.49 and 7.43). The difference in blood pH between the two groups was sustained throughout the sampling period. The average values of arterial and portal blood for base excess and HCO3- content were higher (P < 0.001) at high dEB (6.96 and 31.0 mmol/L, respectively, for -100 mEq/kg and 12.54 and 35.9 mmol/ L, respectively, for 200 mEq/kg). The Na concentration in the blood was increased and K and Cl- concentrations were decreased (P < 0.02) by increasing dEB from -100 mEq/kg to 200 mEq/kg. Blood electrolyte balance level was higher (P < 0.001) in the 200 mEq/kg dEB group than in the -100 mEq/kg dEB group. In conclusion, dEB changed blood oxygen content and pH, and influenced the acid-base buffer system in pigs. Also, within each group, pigs maintained a relatively constant blood pH level during the 9-h period after feeding.

The absence of adequate techniques for rearing fish larvae constitutes a bottleneck for sustainable aquacultural growth. Important constraints are the tiny size of the larvae, the dependance on live food organisms and the developmental stage of the fish larvae. The development of dependable rearing techniques requires knowledge of the critical aspects in nutrition in relation to the development of the digestive and metabolic system. In the present study, this relation between fish nutrition and development was investigated using the African catfish Clarias gariepinus (Burchell) as research model. The study was subdivided into three phases, dealing respectively with husbandry conditions, developmental aspects and with the lipid metabolism. During the first phase, in a comparative study with different dry diets, the dependance of African catfish larvae on live food organisms (e.g., Artemia ) was demonstrated. A technique to estimate quantitative food rations was developed and used to elucidate the quantitative relations between food ration, water temperature and growth. African catfish larvae can be successfully weaned to a dry diet without growth loss provided that they receive live food organisms during the first four days of exogenous feeding. Durint the second phase of the project, the morpho-functional development of the digestive system and the activities of metabolic enzymes were investigated. The results indicated that at the onset of exogenous feeding, African catfish larvae can eat, digest, absorb and metabolize the absorbed nutrients. The changes in feeding habits were correlated with the development of stomach functions. Together with this functional development of the stomach, several other ontogenetic changes in the larval physiology occurr. This combined change of ontogenetic events occurs at a body size of approximately 10-20mg. Therefore this size is suggested as a marker for the end of the larval period in C. gariepinus . The different studies on the lipid metabolism, carried out during the third phase, showed that the eggs of African catfish contain moderate amounts of lipid of a high polar nature (70- 75% of the lipid consist of phosphatidylcholine, PC). PC is an important energy source during the early life stages of this species. African catfish is capable to biosynthesize important n -3 highly unsaturated fatty acids (HUFA) from the yolk sac period onwards. Dietary enrichment with n -3 HUFA does affect liver ultrastructure. It does not influence growth and survival. Consequences of these results for defining an optimal feeding and rearing strategy for larval fish are discussed.