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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.

Balance trials were conducted with African catfish Clarias gariepinus to assess the effect of phytase treatment of soybean meal-based diets on growth, feed utilization and nutrient budgets. Isocaloric (20-22 kJ g(-1)) and isonitrogenous (47-50% protein) diets were tested. In a first experiment the control diet (58% fish meal and 18% soybean meal) was compared with two diets containing 6% fish meal and 69% soybean meal, and two diets containing 29% fish meal and 41% soybean meal. One of each of these two diets had been pretreated with phytase (1000 units per kg dry diet). In the second experiment, the control diet (6% fish meal and 69% soybean meal, pretreated with 1000 units phytase kg(-1) dry diet) was compared with four diets that were similar in composition but supplemented with increasing amounts of phytase(15, 380, 750, 1000 units kg(-1) dry diet). Replacement of fish meal by soybean meal in the first experiment led to a depression in growth rate and feed utilization parameters. Results of both experiments clearly indicated a positive effect of phytase treatment, particularly on phosphorus digestibility and retention, and consequently the phosphorus conversion efficiency and the phosphorus budget. No differences in these parameters were found between addition of equal amounts of phytase by pretreatment or supplementation.

European eel (Anguilla anguilla) were fed either high or low ration levels (1.33 and 0.48% body weight·day1). Eight periods of continuous 24-h respirometry in flow-through conditions were conducted over 70 days to simultaneously examine nitrogen and energy budgets without resorting to the calculation of parameters by difference. Food and oxygen consumption; ammonia, urea, and nitrate-nitrite excretion; and growth production were measured. Nitrogen budgets successfully accounted for 89.6-101.2% of the consumed nitrogen. Energy budgets accounted for 53.4-92.3% of the consumed energy. From the ammonia quotients (AQ), 54.4-57.7% of the available protein was oxidized at high ration, and 59.7-133.5%, at low ration level. To satisfy maintenance requirements, 0.28 mg N·g-1·day-1 was required. At 25°C eels were calculated to have a rate of standard metabolism of 83.3 J·g1·day-1, which is comparable with the range published for other species at this temperature. These data suggest that eels do not have a particularly low metabolic rate, as is commonly assumed in the eel rearing industry, and that the relatively inactive lifestyle associated with the eel masks a metabolic rate in common with other, more active, fish.

The present paper deals with the effect of abiotic environmental stressors on metabolism and growth of fish. Although generally the effect of environmental stressors on metabolism is apparent, the extrapolation to growth is not always evident. In stress research it is often difficult to establish borderline levels for chronic stress, so that increased levels of cortisol are used instead to determine when an environment becomes stressful. Because of the observed inconsistency between increased cortisol levels and depressed growth, the question can be raised as to whether cortisol is the most suitable parameter for measuring chronic stress in this context. The absence of a relationship between selected high or low cortisol response lines and growth indicates that differences between experimental animals should also be considered, particularly with respect to the innate stress response. Whether, in view of the possible existence of alternative coping styles, this automatically involves growth, is unclear.

Pubertal female Clarias gariepinus (recipients) were exposed for 62 days to holding water from intact, completely castrated, seminal vesicles-extirpated or testes-extirpated adult male or from intact adult female conspecifics (donors). In operated male donor groups, levels of six androgens (measured by RIA) were lowest in testes-extirpaied and completely castrated males. However, even complete absence of the testes (GSI 0%) did not eliminate circulating androgens. Male holding water exerted primer pheromonal action in enhancing ovarian development of recipient females, irrespective of the male donor group. Holding water from female donors was ineffective, comparable to controls (fresh water). Thus, although the effect of holding water is linked to the male gender, the gonadal origin of ovarian growth-stimulating compounds in the holding water could not be demonstrated.

Stimulation and inhibition of gonadal development by intersexual contact was studied in pubertal African catfish, Clarias gariepinus. The effect of a possible interaction was studied by evaluation after a 98-day experimental period of gonadal development in combinations of intact and anosmic males and females. In addition, separate groups of males and females, respectively, were exposed to holding water from these combinations. A tentative model of stimulation of gonadal development by intersexual contact in pubertal fish was developed. Males stimulate ovarian development of females by both olfactory and tactile cues. In addition, males seem to enhance gonadal development of other males through olfactory stimulation via holding water. In contrast, females tended to inhibit male gonadal development, especially through tactile cues. It seems that although males are hampered by female tactile stimuli in their gonadal development and ability to stimulate male gonadal development, their ability to stimulate female gonadal development is not affected.

1. 1. Pubertal vitellogenic and previtellogenic female Clarias gariepinus were exposed to holding water from a mixed-sex population of adult conspecifics. 2. 2. Exposure to holding water caused an accelerated ovarian growth in both cases. 3. 3. Analysis of holding water by gas chromatography and mass spectrometry (GCMS) yielded the presence of several steroids and steroid glucuronides known to be produced in adult, prespawning C. gariepinus . 4. 4. The possible role of these compounds in stimulating ovarian growth is discussed in relation to earlier findings on their pheromonal properties.

Different chemical treatments were tested to improve the nutritional value of coffee pulp (CoP): (1) alkali, NaOH solutions of 5 and 10% for 24 and 48 h; (2) a combination of acid and alkali, with first a treatment with HCl (1.5 and 3 M for 24 and 48 h), followed by a NaOH solution of 5% for 48 h; (3) A combination of alkali and ensilage, with first a treatment with a NaOH solution of 5% for 48 h, followed by ensilage with molasses (50 and 100 g molasses/kg of CoP) for 2 and 3 months. The CoP treated with NaOH alone or with the combination HCl–NaOH showed higher contents of ash, fat and cellulose but lower contents of antinutritional factors (ANFs) (polyphenols, tannins and caffeine) than oven-dried-CoP (OD-CoP) (P < 0.05). The true protein content in the CoP was not affected by the alkali treatment but was reduced in the acid–alkali treated CoP compared to OD-CoP. A combined treatment with alkali-ensilage resulted in higher true protein, fat and ash contents (P < 0.05) and in similar contents of cellulose than in OD-CoP. Polyphenols, tannins and caffeine contents were lower in treated CoP than in OD-CoP, but there was no difference in the size of the effect for caffeine between one treatment to the other. The higher ash content found in alkali-ensiled CoP could result from the addition of the alkali. The reduction of ANFs was much higher in the chemical treated CoP than in the alkali-ensiled CoP. The alkali treatment yielded the best overall results in upgrading the nutritive value of CoP. © 2002 Elsevier Science B.V. All rights reserved. Se probaron diferentes tratamientos químicos para mejorar el valor nutricional de la pulpa de café (CoP): (1) soluciones alcalinas, NaOH al 5 y 10% por 24 y 48 h; (2) una combinación de ácido y álcali, con primero un tratamiento con HCl (1.5 y 3 M por 24 y 48 h), seguido de una solución de NaOH al 5% por 48 h; (3) Una combinación de álcali y ensilaje, con un tratamiento primero con una solución de NaOH al 5% durante 48 h, seguido de ensilaje con melaza (50 y 100 g melaza/kg de CoP) durante 2 y 3 meses. Los CoP tratados con NaOH solo o con la combinación HCl-NaOH mostraron mayores contenidos de cenizas, grasa y celulosa pero menores contenidos de factores antinutricionales (FNA) (polifenoles, taninos y cafeína) que los CoP secados al horno (OD-CoP) ( p < 0,05). El verdadero contenido de proteína en el CoP no se vio afectado por el tratamiento con álcali, pero se redujo en el CoP tratado con ácido-álcali en comparación con OD-CoP. Un tratamiento combinado con ensilado alcalino dio como resultado un mayor contenido verdadero de proteína, grasa y cenizas (P < 0,05) y un contenido similar de celulosa que en OD-CoP. Los contenidos de polifenoles, taninos y cafeína fueron menores en los CoP tratados que en los OD-CoP, pero no hubo diferencia en el tamaño del efecto de la cafeína entre un tratamiento y el otro. El mayor contenido de cenizas encontrado en CoP ensilado con álcali podría deberse a la adición del álcali. La reducción de ANF fue mucho mayor en el CoP tratado con productos químicos que en el CoP ensilado con álcali. El tratamiento con álcali arrojó los mejores resultados generales en la mejora del valor nutritivo de CoP. © 2002 Elsevier Science B.V. Todos los derechos reservados. Universidad Nacional, Costa Rica Escuela de Ciencias Biológicas

The postprandial excretion pattern of ammonia in dependence of feeding regime (fasting, 1 ×/day, 2 ×/day, 4 ×/day and continuous feeding), was determined in rainbow trout (Oncorhynchus mykiss), using continuous flow analysis. In fed fish ammonia peaked c. 7 h after the first meal with no differences in pattern between treatments. Fasting fish did not show a pattern. Overall production rates (NH4 and NO2+ NO3) ranged from 0.29–0.31 g kg−1 BW/d in fed fish and were around 0.07 g kg−1 BW/d in fasting fish. Additionally determined total N (Kjeldahl) showed much higher values in fed fish (0.78–1.05 g kg−1 BW/d) but only slightly higher values in fasting fish (0.11 g kg−1 BW/d). Budgets of nitrogen (N) and energy (E) showed low recoveries (c. 50% and between 50% and 70%, respectively). When correcting ammonia excretion (NH4 and NO2+ NO3) using literature data on urea excretion of O. mykiss and assuming that total N partly stemmed from uneaten but undetected feed, both N and E budgets reached a recovery of around 100% in all four fed groups. Implications of this approach are discussed in the light of incomplete budgets as determined in earlier studies.

1. 1. In teleost fish, sex pheromones are involved in advanced phases of reproduction, priming actions influencing oocyte maturation and ovulation in females, and spermiation in males; releasing actions involving attraction of prospective mates and triggering spawning behavior and release of gametes. 2. 2. In the African catfish Clarias gariepinus, sex pheromones were recently demonstrated to also influence earlier phases of the gonadal cycle, i.e. ovarian development in females. 3. 3. Aspects of interaction between sexes in emission of the pheromones, their source and identity are reviewed. 4. 4. The possible function of pheromonal stimulation in the natural environment and implications for fundamental and applied research methodologies are discussed.

Vitellogenesis was monitored in Clarias gariepinus females during puberty and after artificially induced ovarian recrudescence. In two experiments (with pubertal and adult females, respectively), the effect of male stimulation of vitellogenesis was assessed by weekly sampling of females kept with males of exposed to male+female holding water. The parameters examined were the gonadosomatic index (GSI), the proportion and diameter of exogenous vitellogenic oocytes, and plasma levels of estradiol (E2) and vitellogenin (VTG). In pubertal females the pattern and sequence of appearance of these parameters are in general agreement with data from other teleosts: a peak in E2 values precedes a peak in VTG, resulting in an increase of GSI and in a concomitant change in yolk deposition in the oocytes. Stimulation causes both a shift in timing and an increase in levels of plasma E2 and VTG, resulting in faster ovarian growth. In adult females, stimulation of vitellogenesis, although resulting in distinct differences in GSI and ovarian development, is not accompanied by a shift in timing of plasma E2 and VTG. E2 values tend to be higher in stimulated adult females. These differences between first and subsequent cycles are thought to be due to the extremely short recrudescence period of C. gariepinus in captivity.

Adult female African catfish, Clarias gariepinus , were manipulated to enter the phase of ovarian recrudescence by induced ovulation and stripping. These females were exposed to various conspecific stimuli for 33 days. At the end of the experimental period, gonadosomatic indexes (GSIs) were higher in females which had received holding water from a mixed-sex population than in comparable controls. The effect was abolished when recipient females had been rendered anosmic, indicating the presence of chemical substances perceptible through olfaction. Fecundity estimates and histological analysis suggest that the increase in GSI due to pheromonal stimulation is caused by both an increased recruitment of oocytes into the stage of exogenous vitellogenesis and by an enhanced deposition of yolk material in the oocytes. It is concluded that male C. gariepinus release pheromones with a stimulatory effect on vitellogenesis. Neither anosmia itself nor metabolites in holding water affected ovarian recrudescence or body weight increase. The biological significance of such pheromones is discussed in the context of observations on reproduction of C. gariepinus made in the natural environment.

Ovarian growth in pubertal African catfish was followed during a 100-day period. Different combinations of male sensory stimuli resulted in three distinct levels of ovarian development. A basic level (ovarian weight 5.3–7.5 g; GSI 1.9–2.7%) was reached in controls (no contact with males) and in females having visual and auditory contact with males. An intermediate level (ovarian weight 11 g; GSI 4%) was reached if olfactory contact with males was possible. A maximum level (ovarian weight nearly 20 g; GSI 7.3%) resulted from unlimited contact between the two sexes. The question is discussed whether the difference between maximum and intermediate levels of ovarian growth should be ascribed to a better water quality due to experimental conditions rather than to the presence of male tactile stimuli. The possible existence of male primer pheromones responsible for the observed stimulation of ovarian growth in pubertal African catfish by enhancing vitellogenesis is also discussed.