Non-commercial invertebrate discards in an experimental trammel net fishery

Abstract  Non-commercial invertebrate discards in an experimental trammel net fishery were studied in relation to selectivity of the gear, depth, soak time and season. Forty experimental fishing trials were carried out over a 1-year period with six combinations of small mesh (100, 120 and 140 mm) inner and large mesh (600 and 800 mm) outer panels. On average, 43.8 ± 12.2 (SD) (individuals 1000 m⁻¹ of net) of non-commercial invertebrates were discarded, accounting for 48% and 65% of the total catch and total discards by numbers, respectively. Within non-commercial invertebrates discards, the six most abundant species by number were Phallusia mammillata (Cuvier) (27.5%), Cymbium olla (L.) (13.0%), Sphaerechinus granularis (Lamarck) (11.3%), Paracentrotus lividus (Lamarck) (10.9%), Astropartus mediterraneus (Risso) (8.2%) and Astropecten aranciacus (L.) (8.1%); Echinoderms (43.1%) particularly important. The highest and lowest discard ratios were found in autumn and winter, respectively. Discards generally decreased with depth, varied considerably in relation to soak time and were not related to mesh size combinations. Trammel nets seem to be the most important gear in terms of ecological impacts on benthic invertebrates compared with other coastal fishing gears and at the depths studied (15–60 m).     

Non-specific immunity parameters and the formation of advanced glycosylation end-products (AGE) in rainbow trout, Oncorhynchus mykiss (Walbaum), fed high levels of dietary carbohydrates

The effects of long-term hyperglycaemia (5 months), through feeding high levels of dietary carbohydrates, on the non-specific immunity parameters of rainbow trout, Oncorhynchus mykiss (Walbaum), was assessed. Fish were fed one of three diets composed of a basal diet containing ≈ 14% digestible carbohydrate which was progressively diluted with gelatinized potato starch in the following ratios of basal diet to supplemental carbohydrate (gelatinized potato starch): 65:00, 65:20, 65:35. The three diets were pair-fed based on the feed intake of the fish fed the diet containing the highest level of starch (65:35) and representing 100% intake. The other diets were then fed at different levels in a manner that allowed all the groups of fish in the same block to receive the same amount of the basal diet [e.g. the basal diet (undiluted, 65:00) was fed at 65% of the dietary intake of the 65:35 diet]. Blood glucose concentrations and relative liver-to-body size increased with increased dietary carbohydrate intake. Feeding supplemental carbohydrates resulted in a small increase in weight gain of the fish at both supplemental levels. Pronephros tissue lysozyme activity and pronephros macrophage superoxide production were not affected by the dietary treatments. The results suggest the presence of advanced glycosylation end-products in muscle tissue collagen, but were not significantly different between treatments. No substantial effect of long-term feeding of a high carbohydrate diet on the non-specific immunity of rainbow trout was observed. However, the results suggest that dietary carbohydrates may have a slight stimulatory effect on phagocytosis at low–moderate levels.     

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.     

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.     

Trophic relationships and ecosystem characteristics in a newly-impounded man-made lake in Thailand

Abstract  The trophic dynamics of a newly-impounded south east Asian reservoir, Pasak Jolasid, Thailand, monitored from its creation, were constructed using ecopath , a mass-balanced model. The trophic levels (TLs) of 36 ecological groups varied between 1.0 and 3.2. The majority of fish biomass was at the second TL, where the fishery is concentrated. Some food resources (benthic organisms and zooplankton) were not fully used, whereas phytoplankton and benthic algae were important components of the food web, which is based on phytoplankton and detritus. The implications of these findings are discussed in terms of ecological maturity of the ecosystem and possible fishery management of this multi-purpose reservoir.     

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.     

The effects of using crab zoeae (Maja brachydactyla) on growth and biochemical composition of Octopus vulgaris (Cuvier 1797) paralarvae

Octopus vulgaris farming at large scale can only be attained using live prey during the paralarvae stage. Presently, only Artemia complies with this requirement. Nevertheless, its sole use delivers poor paralarvae growth and survival. Some species of marine zooplankton are better prey for marine fish larvae compared to Artemia, since its composition is richer in several important nutritional components. Among these are phospholipids and specific fatty acids, namely docosahexaenoic acid, eicosapentaenoic acid and arachidonic acid. During the present experiment, octopus paralarvae were fed a co-feeding scheme of spider crab (Maja brachydactyla) zoeae and Artemia (1:2, Artemia/Crab zoeae). The use of spider crab zoeae was justified by their availability in commercial facilities, where adult spider crabs are maintained to be sold to the public. There, fecund and spawning females are present in large numbers, and zoeae availability is often high and implies no production or zoeae collection costs. O. vulgaris paralarvae fed on Artemia and crab zoeae grew larger (3.00 ± 0.56 mg dw^?1) after 30 days, compared to previous published papers. Also, the paralarvae lipid content was substantially enhanced in highly unsaturated fatty acids and phospholipids. However, survival after 30 days was still very low (1.75 % after 30 days) and needs to be greatly improved.     

Modelling changes in the length–frequency distributions of fish larvae using field estimates of predator abundance and size distributions

The goal of this study is to determine if an individual-based size-dependent model can realistically simulate changes in the length–frequency distributions of several species of fish larvae collected in Conception Bay in 1993 and 1994, using field estimations of growth and predator abundance. We first model the length–frequency distribution of field samples with the best possible estimates of mean growth rate. Then, we add predation mortality given the characteristics of the predator community observed during our surveys, which was composed of macrozooplankton and adult capelin. The larval fish community is generally not affected by predation by macrozooplankton, as the average instantaneous mortality rate predicted by the model was 0.004 day^–1. Fish larvae appear to be more vulnerable to predation by the population of adult capelin. We estimate that an abundance of adult capelin ranging between 0.2 and 1.0 individuals per 1000 m^–3 may have a substantial impact on the larval fish community. The predictions of an individual-based model are directly related to the accuracy of estimates of the mean growth rates of the larval fish cohorts. We find that it is difficult to differentiate size-selective removal of individuals from random selection by analysing changes of the length–frequency distributions of the larval fish community.     

The purification and partial characterization of carp,Cyprinus carpio,vitellogenin

A procedure is described for the isolation of intact vitellogenin (c-VTG) from the carp, Cyprinus carpio. VTG was induced in juvenile females using oestradiol-17β and purified from the plasma using a combination of gel-filtration chromatography on Sepharose 6B and ion exchange chromatography on DEAE-cellulose. Purification procedures were conducted at low temperatures (below 9°C) in the presence of the proteolytic enzyme inhibitor aprotinin to prevent degradation. Intact c-VTG had an apparent molecular mass of 390,000 Daltons, but when extracted from plasma in the absence of aprotinin it underwent proteolysis into at least 2 protein fragments (apparent molecular masses of 230,000 and 96,000 Daltons), showing an instability of the native dimer. An amino acid analysis of c-VTG showed that its composition was almost identical to goldfish VTG, a species closely allied to the true carps and also similar to other oviparous vertebrate VTGs. Collectively, these data indicate that using these purification procedures VTG from carp, and probably other teleost species, can be isolated in an intact, highly purified form.     

Combining endophytic fungi and bacteria for the biocontrol of Radopholus similis (Cobb) Thorne and for effects on plant growth

Eight endophytic fungal and bacterial isolates with antagonistic activity against Radopholus similis were evaluated in vivo for their individual and combined effects on biocontrol of R. similis and on the growth of “Grand Naine” cultivar banana plantlets in the greenhouse. Penetration efficiency (PE) of R. similis was between 3 and 21% in 29 biological agents (BAs) treatments, less than the 29% of the nematode-alone control (p ≤ 0.0001); 24 of the BAs treatments did not differ from the PE of 5% for a nematicide control. Twenty nine BAs treatments exhibited antagonistic activity against nematodes which reduced final population levels between 18 and 93%, relative to those on nematode-alone control plants (p ≤ 0.0001), and 14 BAs treatments were statistically similar to the nematicide treatment (88% reduction). Twenty four BAs treatments had increments of plant root biomass ranging from 20 to 58%, greater than the control plants; 37% of the treatments with single and combined BAs inoculations had root length increments ranging from 29 to 54% compared with control and chemical treatment. The nematicide, Terbufos 10GR, did not affect plant growth.