J.A.J. Verreth

Eel migration to the Sargasso: remarkably high swimming efficiency and low energy costs

SUMMARY One of the mysteries of the animal kingdom is the long-distance migration (5000–6000 km) of the European eel Anguilla anguilla L. from the coasts of Europe to its spawning grounds in the Sargasso Sea. The only evidence for the location of the spawning site of the European eel in the Sargasso Sea is the discovery by Johannes Schmidt at the beginning of the previous century of the smallest eel larvae (leptocephali) near the Sargasso Sea. For years it has been questioned whether the fasting eels have sufficient energy reserves to cover this enormous distance. We have tested Schmidts theory by placing eels in swim tunnels in the laboratory and allowing them to make a simulated migration of 5500 km. We find that eels swim 4–6 times more efficiently than non-eel-like fish. Our findings are an important advance in this field because they remove a central objection to Schmidts theory by showing that their energy reserves are, in principle, sufficient for the migration. Conclusive proof of the Sargasso Sea theory is likely to come from satellite tracking technology.

Soybean meal induces intestinal inflammation in common carp (Cyprinus carpio L.).

The development of soybean meal (SBM) induced enteritis in the hindgut of the omnivorous common carp (Cyprinus carpio L.). The developed condition was assessed when carp, continuously fed on animal protein, were transferred to a diet in which 20% of the protein was replaced by SBM. After week 1, most of the inflammation parameters were already present, but at week 3, a strong aggravation of the condition was observed which included a shortening of the mucosal folds, the disappearance of the supranuclear vacuoles, an increased number of goblet cells, a thickened lamina propria and sub-epithelial mucosa with increased numbers of basophilic granulocytes as well as a decreased uptake capacity of enterocytes (impaired endocytosis and microvilli). Contrary to previous observations made with respect to Atlantic salmon, common carp start to recover from the fourth to the fifth week after switching to SBM feeding. At this stage, the supranuclear vacuoles refill and most of the parameters revert to basal levels. During the enteritis process, a real-time quantitative PCR analysis was conducted to measure the expression of inflammatory and anti-inflammatory cytokine genes in the isolated intraepithelial lymphocytes (IEL). The pro-inflammatory interleukin 1 beta (IL-1 beta) and tumour necrosis factor alpha1 (TNF-alpha1) genes were up-regulated during the inflammation process while the anti-inflammatory interleukin 10 (IL-10) was down-regulated after an initial up-regulation at week 1. Transforming growth factor beta (TGF-beta) expression showed an up-regulation from week 3 onwards despite the high Ct value and the low primer efficiency shown. This study confirms the contribution of IEL (mainly T-like cells) and basophils in the enteritis process. In addition, the results show a clear involvement of up- and down-regulated cytokine genes in both the onset and recovery of the SBM-induced enteritis in the hindgut of carp.

Reducing Water Use for Animal Production through Aquaculture

Animals fed formulated diets indirectly consume large quantities of water. Globally, about 1.2 m3 of water is needed to produce 1 kg of grain used in animal feeds. Cattle in feedlots consume about 7 kg of feed concentrate to gain 1 kg in weight. For pigs this is close to 4 kg and for poultry slightly more than 2 kg of concentrate. Fish or crustaceans require less than 2 kg of grain concentrate for each kg produced, making them the most efficiently producing animals in terms of feed-associated water use. Non-feed-associated water use can also be considerable, and a comparison was made in total water use between aquatic and terrestrial animals. On-farm water use for terrestrial animals, including drinking, but excluding water for cooling animals or cleaning their sheds is only 1% of feed-associated water use. However, on-farm water use in aquaculture can be very high, attaining values of up to 45 m3 per kg produced in ponds. Intensification of aquaculture reduces on-farm water use per kg product, and only intensive aquaculture production systems are equally water-efficient as terrestrial animal farming systems. Within existing aquaculture pond systems reductions in water use can be achieved through (1) selection of feed ingredients that need little water to be produced; (2) enhancement of within-system feed production through periphyton-based technology; and (3) integration of aquaculture with agriculture. Still, these approaches will not make pond aquaculture more water-efficient than terrestrial animal production systems. That can only be attained in recirculating aquaculture systems and systems producing fish as a by-product of wastewater treatment. Currently, the most promising approach is to concentrate on further development of brackish and marine aquaculture, as such systems use small or negligible amounts of non-feed-associated fresh water.

The effect of dietary L-carnitine on the growth performance in fingerlings of the african catfish ( Clarias gariepinus ) in relation to dietary lipid

The effect of dietary L-carnitine on the growth and growth efficiency of African catfish (Clarias gariepinus, Burchell 1822) fingerlings was investigated. Six dietary levels of L-carnitine, varying from the control level (about 125 mg/kg) to 3920 mg/kg, were each tested at two dietary lipid levels (96 and 155 g/kg). The diets were isonitrogenous and were fed to thirty-six experimental groups of 100 fish weighing 5 g at a feeding level of 25.2 g/kg live weight (w)0.8 per d, during 18 d. The average final weight varied from 19.1 to 28.0 g. At a dietary lipid level of 96 g/kg the metabolic growth increased from 30.8 to 36.5 g/kg w0.8 per d. At the higher dietary lipid level the metabolic growth increased from 30.9 to 35.4 g/kg w0.8 per d. To assess the dose-response relationship between dietary L-carnitine and growth performance in the African catfish a linear-plateau model was fitted to the experimental data. According to this model, metabolic growth was at a maximum at L-carnitine levels of 500 mg/kg and above at a lipid level of 96 g/kg and at L-carnitine levels of 684 mg/kg and above at a lipid level of 155 g/kg. The fitted maximum metabolic growth was higher at a dietary lipid level of 96 g/kg (35.9 g/kg w0.8 per d) than at 155 g/kg (34.7 g/kg w0.8 per d). Feed conversion improved significantly with increasing dietary levels of L-carnitine, reaching a fitted plateau at L-carnitine levels of 448.8 and 236.7 mg/kg respectively for the high and low dietary fat levels. Other growth efficiency variables, e.g. protein efficiency ratio, protein retention and energy retention improved accordingly. Taking into consideration that all fish received the same amount of feed, the results of the present study demonstrate that the positive effect of increased levels of dietary L-carnitine is the result of an improved feed utilization, probably because of a stimulated protein-sparing action.

A comparative study on the nutritional quality of decapsulated Artemia cysts, micro-encapsulated eng diets and enriched dry feeds for Clarias gariepinus (Burchell) larvae

Abstract The nutritional value of several dry test diets for larvae of the African catfish, Clarias gariepinus , was determined. Dried and decapsulated cysts of Artemia gave consistently the best growth and survival rate (over 100 mg and 96%, respectively, after 2 weeks). Dry larval feeds enriched with an acetone extract of Artemia resulted in low growth and extremely low survival rates (less than 20%). The hepatocyte ultrastructure indicated a nutritional deficiency in this diet. Microencapsulated egg diets resulted in high survival rates (varying between 64 and 93%) but low and varying growth rates. The best growth was attained after addition of casein and a vitamin/mineral mix to the egg diet. The hepatocyte ultrastructure revealed a shift from a glycogen to a lipid-based metabolism, which is related to the high fat content of the egg diets. According to the hepatocyte structure, the egg diets provide all essential nutrients. It is therefore hypothesized that the low growth is caused by a decreased feed intake which again may be related to the high fat content of the diets.

The Biology and Economics of Coral Growth

To protect natural coral reefs, it is of utmost importance to understand how the growth of the main reef-building organisms—the zooxanthellate scleractinian corals—is controlled. Understanding coral growth is also relevant for coral aquaculture, which is a rapidly developing business. This review paper provides a comprehensive overview of factors that can influence the growth of zooxanthellate scleractinian corals, with particular emphasis on interactions between these factors. Furthermore, the kinetic principles underlying coral growth are discussed. The reviewed information is put into an economic perspective by making an estimation of the costs of coral aquaculture.

Time‐related changes of the intestinal morphology of Atlantic salmon, Salmo salar L., at two different soybean meal inclusion levels

Abstract Soybean meal (SBM) induces enteritis in the distal intestine of Atlantic salmon. The present study assesses the effects of SBM concentrations on the kinetics of the enteritis process. Fish of 300 g, kept at 12 degrees C, were fed diets with different SBM inclusions: 0%, 10% and 20% SBM for 57 days. Samples of the distal intestine of five fish per treatment were taken for histological and electron microscopical analysis. A semi-quantitative scoring system was used to assess the degree of the morphological changes induced by SBM feeding in the distal intestinal epithelium. The first signs of enteritis appeared earlier in the salmon fed the 20SBM diet than in those fed the 10SBM diet. Thereafter, the condition increased steadily, displaying no signs of recovery. Furthermore, at the lower concentration, the process marking the onset of enteritis began more gradually than at the higher concentration and it displayed a tendency to stabilize after 13-20 days of continuous feeding. Electron microscopy indicated that the endocytosis process was hampered at day 3 of 20SBM and at 7 days of 10SBM. Furthermore, a strong reduction of microvilli was already evident after 7 days of 20SBM feeding, thus indicating a decreased uptake capacity of the distal enterocytes. In addition, transformation and migration of eosinophilic granulocytes was observed, which, in combination with the lysozyme C immunoreactivity supports their protective role during the inflammatory process in the distal gut of Atlantic salmon. It can be concluded that the severity of enteritis and its kinetics are concentration-dependent, showing no signs of recovery during feeding with diets containing SBM.

Biochemical and enzymatic characterization of decapsulated cysts and nauplii of the brine shrimp Artemia at different developmental stages

Abstract Decapsulated Artemia cysts were used to study the factors which induce the superior performance of live organisms as food for fish larvae. The biochemical composition, the in vitro protein digestibility, and the total proteolytic and trypsin activities in cysts and nauplii of Artemia were determined at different developmental stages as a function of incubation time. Six different incubation times were studied: 1, 6, 11, 16, 21 and 25 h of development, which cover cyst and early nauplii stages. The individual dry weight of Artemia decreased through development. The individual protein and lipid content ( μ g ind −1 ) remained constant during development until the time of hatching after which they decreased slightly. However, no significant incubation effect was found. Small changes in amino acid and fatty acid composition were found during development, but is assumed that they are too small to be of nutritional importance to fish larvae. No major changes were observed in protease activities measured at acid and alkaline pH during the first 25 h of development. From the alkaline proteases, no significant change in trypsin activity was detected during cyst and early nauplii development. From the point of view of exogenous enzyme contribution to fish larvae, there seems to be no difference whether feeding decapsulated cysts or newly hatched nauplii, since no difference in qualitative protease composition was found during the first 25 h of Artemia development. The relative contribution of Artemia proteases to the digestion of food by fish larvae is discussed.

Amino acid profiles and amino acid utilisation in larval African catfish (Clarias gariepinus): effects of ontogeny and temperature.

The present study investigated the qualitative amino acid (AA) requirements of larval African catfish Clarias gariepinus. Yolk-sac larval AA profiles were measured at different temperatures and also in animals reared at 28 °C fed Artemia nauplii or an experimental dry diet. The AA profile of C. gariepinus larvae changed during ontogeny, especially before the start of exogenous feeding. The AA profiles of the food items (yolk, Artemia and the dry diet) differed considerably from that of the larvae. No selective absorption of yolk AA was detected. Higher temperatures led to increased absorption and depletion rates of AA, and also to a higher retention efficiency of yolk nutrients. However, changes in temperature did not induce preferential absorption or depletion of individual AA, and caused only small variations in the AA profile. Depletion rates of individual AAs varied, possibly due to differences between larval and yolk AA profiles, and also to changes in the larval AA profile during ontogeny. There was little regulation of catabolism of individual AA in yolk-sac and starved larvae, and no sparing of essential AA.

Metabolic enzyme activities in larvae of the African catfish, Clarias gariepinus: changes in relation to age and nutrition

The influence of ontogeny and nutrition on metabolic enzyme activities in larvae of the African catfish, Clarias gariepinus, was studied. After start of exogenous feeding, the larvae were reared for 10 days under three different nutritional conditions: Artemia nauplii, a dry starter diet, and starvation. The live feed gave the best growth (96 mg within 10 days) whereas the dry diet resulted in low growth (33 mg). This growth difference was reflected in larval RNA and DNA concentrations, but not in the levels of soluble protein. Enzymes representing the following aspects of metabolism have been analysed: NADPH generation (G6PDH, ME), glycolysis (PFK, PK), gluconeogenesis (FDPase), amino acid catabolism (GOT, GPT) and oxidative catabolism (CS). All enzymes were present from the start of exogenous feeding onwards, but their maximum specific activities displayed different developmental patterns. In catfish larvae fed on Artemia, G6PDH and ME activities steadily increased with age and weight of the larvae. CS levels remained, after an immediate enhancement upon onset of exogenous feeding, on a rather stable plateau. The amino acid-degrading enzymes GOT and GPT showed maximum levels at days 3–5 of feeding or at a body weight of 10–20 mg, but decreased thereafter. Activities of PFK, PK and FDPase showed low initial levels, and increased significantly with age and size. Based on the ontogenetic patterns of metabolic enzymes, in C. gariepinus larvae an early and a late developmental phase can be distinguished. During the early phase, the glycolytic and gluconeogenetic capacities are low, whereas they are enforced during the later phase. The oxidative capacity is high both during the early and the late phase. The metabolic changes in catfish development coincide with other major ontogenetic events, e.g., alterations of muscle organization, gill morphology, respiration and stomach structure and function. Rearing catfish larvae on a dry diet instead of Artemia partly altered the developmental pattern described: The ontogenetic elevation of CS, PFK and FDPase was delayed and the early peak in GOT and GPT activities was not realized. Particularly during the early developmental phase, the enzyme behaviour of the larvae fed on dry food was similar to that of starved larvae.