Tropical agricultural residues and their potential uses in fish feeds: the Costa Rican situation.

In Costa Rica as many other tropical countries, the disposal problem of agricultural wastes is widely recognized but efforts to find solutions are not equal for different sectors. This study describes the situation of major agricultural residues in Costa Rica, identifying the activities with higher amounts produced and, the potential use of these residues in fish feeds. In Costa Rica, during the 1993-1994 production season, major agricultural sectors (crop and livestock) generated a total amount of 3.15-3.25 million MT of residues (classified in by-products: used residues and wastes: not used residues). Some residues are treated to turn them into valuable items or to diminish their polluting effects (e.g., the so-called by-products). About 1.56-1.63 million MT of by-products were used for different purposes (e.g. fertilization, animal feeding, fuel, substrates in greenhouses). However, the remainder (1.59-1.62 million MT) was discharged into environment causing pollution. About 1.07-1.2 million MT wastes came from major crop systems (banana, coffee, sugarcane and oil palm) whereas the remainder came from animal production systems (porcine and poultry production, slaughtering). These data are further compared to residues estimates for the 2001-2002 production season coming from the biggest crops activities. Unfortunately, most of the studied wastes contain high levels of moisture and low levels of protein, and also contain variable amounts of antinutritional factors (e.g., polyphenols, tannins, caffeine), high fibre levels and some toxic substances and pesticides. All these reasons may limit the use of these agricultural wastes for animal feeding, especially in fish feeds. The potential use of the major vegetable and animal residues in fish feeds is discussed based on their nutritional composition, on their amount available over the year and on their pollution risks. Other constraints to use these wastes in fish feeds are the extra costs of drying and, in most cases, of transportation from several dispersed locations. It was stated that most interesting wastes are rejected green banana and coffee pulp.

Biological treatments affect the chemical composition of coffee pulp.

Biological treatments were applied to fresh coffee pulp (CoP) to improve its nutritive value for monogastric animals by reducing its content of cellulose and antinutritional factors (ANFs) such as total phenols, tannins and caffeine. Treatments were: (1) ensiling with 0, 50 and 100 gkg(-1) molasses for 2 and 3 months, (2) aerobic decomposition for 0, 7, 14, 21, 28, 35 and 42 days, (3) aerobic bacterial inoculation (Bacillus sp.) for 0, 7, 14, 21 and 28 days. Ensiled CoP (E-CoP) showed higher fat and ash contents than oven-dried-CoP (OD-CoP; P<0.05). Similarly, true protein values tended to increase. The cellulose and total phenols levels of E-CoP were lower than OD-CoP (P<0.05). The E-CoP tannins levels tended to be lower than OD-CoP whereas caffeine levels remained unaffected. Improvement in the nutritional quality of E-CoP was associated with higher fat and protein contents and reduction of cellulose, total phenols and tannins. The aerobic decomposition treatment improved the nutritional quality of CoP by increasing true protein and fat contents. In addition, total phenols, tannins, caffeine and cellulose contents were reduced by an increase in treatment time (P<0.05). Bacterial treatment increased the protein content of CoP after 21 days (from 137 to 392 gkg(-1)) and decreased it after 28 days. Cellulose, total phenols, tannins and caffeine contents reduced with an increase in time of bacterial degradation. Bacterial treatment improved the CoP quality by increasing protein content and reducing cellulose and ANFs, especially after 21 days of treatment. Both the aerobic decomposition (after 21-28 days) and the aerobic bacterial degradation of CoP (after 21 days) appeared more suitable to improve the nutritional quality of CoP than the ensiling.

Preliminary study on haemocyte response to white spot syndrome virus infection in black tiger shrimp Penaeus monodon.

White spot syndrome virus (WSSV) has been a major cause of shrimp mortality in aquaculture in the past decade. In contrast to extensive studies on the morphology and genome structure of the virus, little work has been done on the defence reaction of the host after WSSV infection. Therefore, we examined the haemocyte response to experimental WSSV infection in the black tiger shrimp Penaeus monodon. Haemolymph sampling and histology showed a significant decline in free, circulating haemocytes after WSSV infection. A combination of in situ hybridisation with a specific DNA probe for WSSV and immuno-histochemistry with a specific antibody against haemocyte granules in tissue sections indicated that haemocytes left the circulation and migrated to tissues where many virus-infected cells were present. However, no subsequent haemocyte response to the virus-infected cells was detected. The number of granular cells decreased in the haematopoietic tissue of infected shrimp. In addition, a fibrous-like immuno-reactive layer appears in the outer stromal matrix of tubule walls in the lymphoid organ of infected shrimp. The role of haemocytes in shrimp defence after viral infection is discussed.

Changes in fatty acid concentrations in tissues of African catfish, Clarias gariepinus Burchell, as a consequence of dietary carnitine, fat and lysine supplementation.

A study was undertaken to examine the effect of different dietary carnitine (200 and 1000 mg/kg diet) and fat (90 and 190 g/kg diet) supplementation on growth and fatty acid concentrations of fish fed either with a low- (13 g/kg) or a high-lysine (21 g/kg) diet. African catfish (22.7 g/fish), Clarias gariepinus Burchell, juveniles were stocked (sixteen aquaria, twenty-five fish per aquarium) and fed for a maximum of 74 d. Dietary lysine had a clear effect on growth performance and feed conversion ratios, but dietary carnitine supplements had no effect. High-carnitine supplements increased total carnitine content (P<0.0004) and reduced tissue free carnitine: acyl-carnitine ratio (P<0.05) compared with low-carnitine supplements. High-fat supplements decreased liver carnitine concentrations. Clear effects on liver fatty acid concentrations were observed in high-carnitine-fed fish compared with low-carnitine-fed fish. The primary liver fatty acids affected were n-6 (linoleic acid), n-3 (eicosapentanoic acid) and n-3 (docosahexanoic acid). The whole-body fatty acid balance suggested that n-3 disappeared (apparently by beta-oxidation) more readily than n-6 and/or n-3. From 774 mg n-3 eaten by high-lysine-high-fat-low-carnitine fish, 58 % was not assimilated into body tissues. High-carnitine-fed fish showed an increase in n-3 oxidation by 7 % compared with low-carnitine fish. Although dietary carnitine did not improve body growth, these results support the hypothesis that carnitine can enhance the mobilisation of long-chain fatty acids towards oxidation.

Influence of flumequine and oxytetracycline on the resistance of the European eel against the parasitic swimbladder nematode Anguillicola crassus.

The effect of the antibacterial drugs flumequine (FQ) and oxytetracycline (OTC) on the defence system of the European eel (Anguilla anguilla L., 1758) was investigated using an experimentally induced infection with the parasitic swimbladder nematode Anguillicola crassus. Eight weeks after oral administration of infective larvae, the mean recovery of the parasites in FQ-treated eels was lower than in non-medicated control animals, and significantly lower than in OTC-treated eels. Mean numbers of peripheral blood granulocytes and B-lymphocytes, as well as the total number of circulating lymphoid cells, showed a significant increase as a result of the infection, while drug treatment merely affected the quantity of the lymphoid cells. The difference in protection against the parasite after FQ or OTC administration points to a modulation of the fish resistance as a result of the drug treatment. The results favour a modulation of the cellular rather than the humoral response, as no specific antibodies were found.