Incorporation of composted and dried water hyacinth in pelleted feed for the tilapia Oreochromis niloticus (Peters)

Abstract. Eight diets were formulated using either composted or dried water hyacinth, Eichornia crassipes (Mart.) Solms., incorporated into a conventional pelleted tilapia feed in a simple displacement procedure: 100. 75, 50 and 25% composted water hyacinth: 100, 75 and 25% dried water hyacinth; and a control diet with 0% displacement of the conventional feed. The experimental diets were fed in duplicate treatments to Oreochromis niloticus in a series of 16 outdoor 4-m³ tanks stocked with eight fish/tank for 84 days. Good growth and feed utilization efficiencies were obtained with diets containing up to 75% composted water hyacinth with no significant reduction in fish performance compared to the control diet. Fish performed better with diets containing composted than with diets containing dried water hyacinth, except for the 100% composted water hyacinth diet in which the pellet was exceptionally hard. The better performance with diets containing composted compared to dried water hyacinth may have been due to the lower levels of crude fibre in the former diets, although significant fish growth was achieved even with the diet containing 100% dried water hyacinth. Some nutrition must have been obtained by the fish indirectly from the plankton in the static water experimental system but it was concluded that the fish also obtained a significant amount of their nutrition directly from the diets, including those with a high percentage of composted water hyacinth which in some treatments had relatively low mean phytoplankton biomass levels in the water. An experimental protocol is recommended for the evaluation of the nutritional value of non-conventional fish feeds in which determination of fish growth without concern for underlying mechanisms precedes studies to assess the relative contribution of the direct and indirect nutritional value of the feed.     

Passive immunisation of fish against vibriosis, comparison of intraperitoneal, oral and immersion routes

Passive immunisation of fish was conducted to determine whether anti-Vibrio anguillarum whole sera (AVA) and affinity-purified AVA raised in sheep, rabbits and rainbow trout (Oncorhynchus mykiss) were persistent when injected and orally administered into rainbow trout. These responses were compared with active immunisation by immersion in, and intraperitoneal (i.p.) injection with, formalin-killed V. anguillarum cells. Sheep and rabbit AVA were detected in rainbow trout sera for up to 70 days (half-life 21 days) after i.p. injection as determined by an enzyme-linked immunosorbent assay (ELISA). The relative percentage survival (RPS) of passively immunised rainbow trout challenged with virulent V. anguillarum after an injection was comparable to that of active immunisation by immersion after 1 month post-immunisation (p.i). Affinity-purified sheep and rabbit AVA exhibited the same protective potential as whole serum in rainbow trout. Rabbit and sheep immune sera diluted 1:8 and 1:50, respectively, provided equivalent protection as undiluted fish immune serum. An active immune response against passively acquired heterologous immunoglobulins was demonstrated by ELISA, with responses against sheep AVA being less than those against rabbit AVA. Rainbow trout given purified sheep AVA conjugated to LTB (the GM-1-binding subunit of Escherichia coli heat-labile toxin) and administered orally had an RPS of 37.5% at 15 days and 27% at 1 month p.i. In contrast, fish given sheep AVA conjugated to TraT (an internal membrane of E. coli) or in micellar form with Quil-A had RPSs of only 18.7 and 6.2%, respectively, after 15 days, and 13.3 and 0% after 1 month, respectively. The protection conferred by immune sera was shown to be due to the immunoglobulin component alone. Heat inactivation of the complement in sera had no effect on the potency of immune sera.     

Effect of dietary supplementation of inulin and W. cibaria on haemato‐immunological parameters of hybrid surubim (Pseudoplatystoma sp)

The dietary supplementation of prebiotics, probiotics and symbiotic in hybrid surubins (a Pseudoplatystoma corruscans and P. fasciatum cross) was evaluated for the effects on their autochthonous intestinal microbiota and on haematological and immunological parameters. A total of 160 fish were divided into four treatment groups with four replicates each. The treatment groups were fed with the following diets for 15 days: control diet without supplementation; 0.5% inulin (prebiotic) supplementation; Weissella cibaria (CPQBA 001‐10 DRM 02) (7.87 ± 0.2 log CFU g^?1) supplementation; or 0.5% inulin and W. cibaria supplementation (symbiotic group). The midgut intestines of the fish with the symbiotic diet supplementation had higher concentrations of lactic acid bacteria (7.07 ± 1.11 log CFU g^?1) and low levels of Vibrio spp (1.90 ± 0.60 log CFU g^?1) and Pseudomonas spp (2.23 ± 1.48 log CFU g^?1). In addition, increased erythrocytes and reduced circulating neutrophils were observed in this group. No differences in blood glucose, serum protein or lysozyme levels were detected between treatment groups. However, a higher concentration of total immunoglobulin was observed in fish fed with the probiotic and symbiotic diets. The addition of 0.5% inulin (prebiotic) thus W. cibaria (probiotic) to the diet of Pseudoplatystoma hybrid surubins reduce the number of pathogenic bacteria and stimulate the beneficial intestinal microbiota and may possibly alter their immune defence system.     

Age and growth of female eels, Anguilla angilla L., in a Polish lake, Jeziorak Lake, Mazurian Lake District, Poland

Abstract. Measurements taken from a series of photographs of otoliths of 37 eels caught in a medium-sized (3219 ha) eutrophic lake in northern Poland were used to prepare a growth curve based on back-calculated measurements. Values of L^∞= 1086 mm; K = 0.048 and mean annual increment = 40.7 mm were determined. A comparison was made of eel growth within its whole range of occurrence.     

Effects of docosahexaenoic, eicosapentaenoic, and arachidonic acids on the early growth, survival, lipid composition and pigmentation of yellowtail flounder (Limanda ferruginea): a live food enrichment experiment

The role of dietary ratios of docosahexaenoic acid (DHA, 22:6n−3), eicosapentaenoic acid (EPA, 20:5n−3) and arachidonic acid (AA, 20:4n−6) on early growth, survival, lipid composition, and pigmentation of yellowtail flounder was studied. Rotifers were enriched with lipid emulsions containing high DHA (43.3% of total fatty acids), DHA+EPA (37.4% and 14.2%, respectively), DHA+AA (36.0% and 8.9%), or a control emulsion containing only olive oil (no DHA, EPA, or AA). Larvae were fed differently enriched rotifers for 4 weeks post-hatch. At week 4, yellowtail larvae fed the high DHA diet were significantly larger (9.7±0.2 mm, P<0.05) and had higher survival (22.1±0.4%), while larvae fed the control diet were significantly smaller (7.3±0.2 mm, P<0.05) and showed lower survival (5.2±1.9%). Larval lipid class and fatty acid profiles differed significantly among treatments with larvae fed high polyunsaturated fatty acid (PUFA) diets having higher relative amounts of triacylglycerols (18–21% of total lipid) than larvae in the control diet (11%). Larval fatty acids reflected dietary levels of DHA, EPA and AA while larvae fed the control diet had reduced amounts of monounsaturated fatty acids (MUFA) and increased levels of PUFA relative to dietary levels. A strong relationship was observed between the DHA/EPA ratio in the diet and larval size (r²=0.75, P=0.005) and survival (r²=0.86, P=0.001). Following metamorphosis, the incidence of malpigmentation was higher in the DHA+AA diet (92%) than in all other treatments (50%). Results suggest that yellowtail larvae require a high level of dietary DHA for maximal growth and survival while diets containing elevated AA exert negative effects on larval pigmentation.     

Effect of ammonia on the growth rate and oxygen consumption of juvenile greenlip abalone, Haliotis laevigata Donovan

Juvenile greenlip abalone, Haliotis laevigata, (mean whole weight 4.48±1.9 g, mean±s.d., n=953) were highly sensitive to ammonia as indicated by depressed growth rate and food consumption measured over 2–3 months in bioassay tanks. For growth rate expressed on a whole weight basis, the EC₅ and EC₅₀ values (5 and 50% growth reductions) were 0.041 mg FAN l⁻¹ (Free Ammonia–Nitrogen) and 0.158 mg FAN l⁻¹, respectively. Shell growth rates declined over the entire experimental range (0.006–0.188 mg FAN l⁻¹). At the end of the bioassay, groups of abalone were transferred to respiratory chambers. Oxygen consumption rate increased to a maximum of 188% of control values at 0.235 mg FAN l⁻¹ and decreased slightly at the highest concentration of 0.418 mg FAN l⁻¹.     

Biochemical,Physical, Chemical,and Microbiological Assessment of Blue Shrimp (Litopenaeus stylirostris) Stored in Ice

Postmortem changes in blue shrimp (Litopenaeus stylirostris) muscle were studied on the basis of biochemical, chemical, physical, and microbiological changes during an 18 day storage period at 0°C. Adenosine 5′-triphosphate (ATP) content, breakdown products, K-value, pH, trimethylamine nitrogen (TMA-N), total volatile basic nitrogen (TVB-N), water holding capacity (WHC), color, and texture (shear force) changes were examined. Also, total mesophilic and psychrophilic bacterial counts were measured. K-value increased linearly (r² = 0.98) from an initial value of 1.37 ± 0.59 to 59.42 ± 6.05% at Day 18. Spoilage indicators TVB-N and TMA-N increased from 29.56 ± 1.33 and 0.69 ± 0.25 to 39.04 and 2.04 ± 0.59 mg of N/100 g at Day 18, respectively; meanwhile, the total viable counts of mesophilic and psychrophilic bacteria increased from 3.48 ± 0.44 and 2.61 ± 0.29 log CFU/g to 6.27 ± 0.21 and 7.14 ± 0.39 log CFU/g, respectively, which indicated spoilage at the end of the storage period. The pH, texture, WHC, and color were affected (p < 0.05) during the storage period. Overall, results indicate that blue shrimp muscle quality was maintained for 12 days of storage in ice.     

The influence of antibiotics on the immune system: immuno-pharmokinetic investigations on the primary anti-SRBC response in carp, Cyprinus carpio L., after oxytetracycline injection

Abstract. The present study was performed to obtain further details on the immuno-modulating effects of oxytetracycline (OTC) in carp, Cyprinus carpio L. The immuno-logical study was extended by investigating the pharmacokinetic behaviour of OTC. Oxytetracycline, at a dosage of 60 mg/kg, was administered five times intra-peritoneally at 3-day intervals; the first injection was given 1 day before immunization. The kinetics of the primary anti-sheep red blood cell (SRBC) response, during a short-term OTC treatment revealed that the kinetics of the plaque-forming cell (PFC) response was not significantly affected by OTC nor its solvent. In contrast, the number of plaque-forming cells was significantly decreased. The anti-SRBC antibody production was delayed by 2–4 days in both experimental groups (OTC and solvent). However, within 12–14 days post-immunization, the same antibody levels were detected as in the control group. High OTC plasma levels (>50 μg/ml) were detected about 10 h after a single i. p. injection. A mean plasma elimination half-life (T¹/₂) of 34·5 h was calculated.     

Abnormalities in the juvenile stage of sea bass (Dicentrarchus labrax L.) reared at different temperatures: types, prevalence and effect on growth

Osteological malformations are always considered an important problem in intensive aquaculture. This work studies the effect of rearing temperature on malformations in sea bass, Dicentrarchus labrax. To this end, two batches of the species were subjected to the following incubation/cultivation temperatures: 15 °C/natural and 19/19 °C, from fertilization until 190 days after hatching. The different malformations were studied in 1643 juveniles at 190 days and classified by categories. The Chi-square statistic was calculated to verify the relationship between the presence of anomalies and the application of different temperatures. The percentage of anomalies observed in individuals reared at a high temperature (19/19 °C) was 66.44%. In both temperature systems, opercular malformations were those which caused a greater delay in growth. The results found indicated that temperature played a very important role in the development of deformations, which may be of interest from the viewpoint of aquaculture.     

Nutrient digestibility studies in Heteropneustes fossilis (Bloch), Clarias batrachus (Linnaeus) and C. gariepinus (Burchell)

The apparent digestibility coefficient (ADC %) for protein in catfishes, Clarias batrachus (Linnaeus) (16–18 cm; 45–50 g), C. gariepinus (Burchell) (21–22 cm; 60–65 g) and Heteropneustes fossilis (Bloch) (10–12 cm; 10–15 g) was estimated for nine feedstuffs of plant and animal origin. Fat digestibility was tested for C. batrachus and C. gariepinus, wherein the influence of feeding frequency on protein digestibility was also examined. The digestibility trials were conducted with triplicate groups of 25 fish each in 70‐L polyvinyl indoor flow‐through (1–1.5 L min^?1) circular tanks (water volume=55 L). Fish were fed to satiation daily, at 08:00 and 18:00 hours, and faecal matter was collected through slow siphoning. For studying the effect of feeding frequency, fish were fed the experimental diets at 08:00, 11:00, 14:00 and 17:00 hours. The protein digestibility of the feedstuffs varied significantly within each test species. However, the protein digestibility values for most of the ingredients tested were comparable between the three catfish species. The most efficient utilization of protein in these fishes was noted for soybean meal followed by lab‐prepared fishmeal. The lowest protein digestibility was recorded for rice bran. Similarly, the utilization of fat from the feedstuffs was also significantly different within each of the two species, C. batrachus and C. gariepinus. Fat digestibility of feed ingredients was similar between the two species. With respect to the fat, soybean meal, lab‐prepared fishmeal, full‐fat soybean meal and dried fish were more efficiently utilized, while the lowest fat digestibility was obtained for rice bran. A marked decline in protein utilization was observed in the two species where the feeding frequency was increased from two to four times a day.