Effect of different dietary lipid levels on the reproduction of Rhamdia quelen (Quoy and Gaimard, 1824)

Lipids include some of the most important nutrients that affect the survival and growth of fishes in their early life stages. Lipid deficiency prior to spawning may significantly reduce egg production, hatchability and the number of surviving larvae. In this study, we investigated the effects of isocaloric diets containing 80, 140 and 200 g kg⁻¹ of lipids (lipid source, soy oil) for 90 days. The following data were collected at 0, 45 and 90 days: final weight; length; conditioning factor; hepatosomatic, gonadosomatic and visceral fat indices; total plasma protein; testosterone; 17ß‐estradiol; free amino acids; and ovary and muscle fatty acid profiles. Additionally, fecundity, oocyte production, egg morphometric parameters, and larval and postlarval growth were evaluated. Results were not statistically different for husbandry and biochemical parameters, but visceral fat content increased with increase in dietary lipid levels. The fatty acid profiles and composition differed among dietary treatments. The egg diameter and area were significantly low in fish fed the 200 g kg⁻¹ lipid diet, thereby hindering growth, survival and weight compared to those in postlarval fish (P < 0.05). The best reproductive rates were obtained when using diets containing 80–140 g kg⁻¹ total lipids.     

Growth,survival and fatty acid composition of Rhamdia quelen (Quoy and Gaimard, 1824) larvae fed on artificial diet alone or in combination with Artemia nauplii

Black catfish (Rhamdia quelen) is a species of interest for aquaculture in Brazil, Argentina and Uruguay. A feeding trial was conducted to evaluate the effect of feeding R. quelen larvae on either only an artificial diet or in combination with Artemia nauplii (AN) on larval performance and fatty acid composition. For 12 days, larvae were fed from first feeding (3 days after hatching, TL = 5.88 ± 0.23 mm) with artificial food only or a combination of artificial food and AN (co‐feeding). At the end of the trial, total length of co‐fed larvae was significantly higher than that of larvae fed solely artificial food (P < 0.001). No significant differences were found in survival rates. Co‐feeding microdiet with a small amount of AN significantly affected larval fatty acid composition. Lipid and fatty acid composition of food and larvae revealed the importance of n‐3 fatty acids for growth of black catfish larvae and that, as most freshwater fish, R. quelen larvae can elongate and desaturate linolenic acid to n‐3 highly unsaturated fatty acids. Results suggest that R. quelen larvae can be fed from first feeding on microdiets as unique food source, although better larval performances are obtained by co‐feeding with a small amount of AN.     

Survival, growth and biochemical parameters of silver catfish, Rhamdia quelen (Quoy & Gaimard, 1824), juveniles exposed to different dissolved oxygen levels

Silver catfish, Rhamdia quelen (Quoy & Gaimard, 1824), is an endemic species from Latin America that is raised in cultivation ponds, and consequently may be exposed to low oxygen levels. Therefore, the objective of this study was to verify the lethal concentration (CL_{50?96 h}) of dissolved oxygen levels for silver catfish juveniles. In addition, the effects of different dissolved oxygen levels (1.96±0.08, 3.10±0.10, 4.14±0.09, 5.20±0.07 and 6.16±0.03 mg L^?1) on growth and metabolic parameters (glycogen, glucose, protein, lactate levels and catalase activity) were also investigated. CL_{50?96 h} was 0.52 mg L^?1 (CI 0.42–0.61 mg L^?1) or 6.7% oxygen saturation. After exposure of silver catfish to hypoxia for 30 days, there were no changes in biochemical parameters indicating the use of an anaerobic pathway by the fish. However, the dissolved oxygen levels influenced silver catfish juvenile behaviour, survival and growth, and under the experimental conditions 5.2 mg L^?1 (or 65.6% oxygen saturation) is the minimum oxygen level recommended for the growth of this species.     

Replacement of fish oil with vegetable oils in diets for jundiá (Rhamdia quelen Quoy and Gaimard 1824): effects on performance and whole body fatty acid composition

The jundiá (Rhamdia quelen) is a siluriform with great potential for aquaculture in South America. Fish oil is a raw material in diets for fish. However, the fisheries that provide fish oil have reached their limit of sustainability. Thus, the use of alternative sources for this ingredient is primordial. The aim of this study was to evaluate the performance and body composition of the jundiá fed with different sources of the vegetable oils. Jundiá (1.0±0.2 g) were fed for 31 days with five isonitrogenous (37%) and isoenergetic (19 kJ g^?1) diets, in which the following oils were added: 50 g kg^?1 corn oil (CO), 50 g kg^?1 fish oil (FO), 50 g kg^?1 linseed oil (LO), 33.4 g kg^?1 fish oil and 16.7 g kg^?1 linseed oil (1/3LO), 16.7 g kg^?1 fish oil and 33.4 g kg^?1 linseed oil (2/3LO). The performance did not show differences between treatments. The final fatty acid profile and n‐3/n‐6 ratio of the fish were highly influenced by the diet. Fish‐fed diets with linseed and/or fish oil showed superior n‐3/n‐6 ratios to the minimal recommended by the World Health Organization; whereas fish fed diets with corn oil showed an inferior value. Albeit in the present study the commercial size of fish was not attained, these results show a clear tendency. The desaturation/elongation capacity was evidenced, in this species, for the first time. Linseed oil can be utilized as a substitute for fish oil in diets of jundiá without affecting their performance and for producing good‐quality fish. However, more studies are necessary to confirm these results for commercial size.     

Early development of the silver catfish Rhamdia quelen (Quoy & Gaimard, 1824) (Pisces:Heptapteridae) from the São Francisco River Basin, Brazil

The silver catfish, Rhamdia quelen , is endemic to North, Central and South America with high aquaculture potential and wide acceptance in the market. Breeder fish were subjected to induced reproduction through hypophysation using a crude common carp pituitary extract. Egg characteristics, oocyte surface ultrastructure and histology of larval ontogenesis until whole yolk resorption were described for the first time for this species. Oocytes and semen were obtained by manual extrusion, and fertilization was conducted using the dry method. After fertilization, eggs were kept in incubators at 24 °C. The embryonic development was monitored using a stereomicroscope every 10 min until hatching. To analyse the larval development, larvae samples were collected from incubators daily until the fifth day, fixed in Bouin's fluid and subjected to routine histological techniques. The oocyte extrusion occurred 8 h after the second hormone dose at 26 °C. The oocytes were spherical, non-adhesive and yellow, with a diameter of 1471.75±47.63 μm. Scanning electron microscopy revealed a thin jelly coat covering the zona radiata in the animal pole around the micropyle. The blastopore closure occurred within 8 h after fertilization, and the fertilization rate was 79.9±5.2% at 24 °C. Embryonic development was completed within 25 h 30 min after fertilization. The complete resorption of the yolk and the formation of the digestive system organs and the mouth opening occurred on the fifth day, indicating a need for exogenous feeding. The results of this study provide information important for improvement in R. quelen culture and management.     

Silver catfish Rhamdia quelen immersion anaesthesia with essential oil of Aloysia triphylla (L'Hérit) Britton or tricaine methanesulfonate: effect on stress response and antioxidant status

Responses to anaesthesia with essential oil (EO) of Aloysia triphylla (135 and 180 mg L^?1) and tricaine methanesulfonate (MS222) (150 and 300 mg L^?1) were assessed in silver catfish. Exposure to the anaesthetics elicited a stress response in the species. In the case of MS222, it was displayed as a release of cortisol into bloodstream, elevation in hematocrit and plasma ion loss. The EO presented cortisol‐blocking properties, but increased haematocrit and disturbances of hydromineral balance were observed. Liver antioxidant/oxidant status of EO and MS222‐anaesthetized silver catfish was also estimated. The synthetic anaesthetic induced lipoperoxidation, notwithstanding increased catalase contents, whereas the naturally occurring product was capable of preventing the formation of lipid peroxides, possibly due to combined actions of catalase and glutathione‐S‐transferase. Anaesthetic efficacy was also tested via induction and recovery times. Overall, the promising results obtained for the physiological parameters of the EO‐treated fish counterbalanced the slight prolonged induction time observed for 180 mg L^?1. As for 135 mg L^?1, both induction and recovery times were lengthy; despite that, the EO was able to promote oxidative protection and mitigate stress. None of the MS222 concentrations prompted such responses concomitantly.     

Introduction of jundia Rhamdia quelen (Quoy & Gaimard) and Nile tilapia Oreochromis niloticus (Linnaeus) increases the productivity of carp polyculture in southern Brazil

Fish polyculture is based on the assumption that each species has its own feeding niche and may increase the maximum standing crop of a pond by exploring a wider range of available food and ecological niches. In order to identify the better species ratio and to introduce jundia (JN) (Rhamdia quelen Quoy & Gaimard) and Nile tilapia (NT) (Oreochromis niloticus Linnaeus) in to the carp polyculture practiced in South Brazil, a 162‐day experiment was conducted, in 12 250‐m² earthen ponds (1.2 m deep). Treatment I (T‐I) contained 35% common carp, Cyprinus carpio (L.) (CC); 35% grass carp, Ctenopharyngodon idella Valenciennes (GC); 15% silver carp, Hypophthalmichthys molitrix Valenciennes (SC); and 15% bighead carp, Aristichthys nobilis Richardson (BC). Treatment II (T‐II) consisted of three ponds stocked at the following ratio: 17.5% CC, 35% GC, 15% SC, 15% BC and 17.5% JN. Treatment III (T‐III) consisted of three ponds with 35% CC, 35% GC, 7.5% SC, 7.5% BC and 15% NT. Treatment IV (T‐IV) consisted of three ponds with 17.5% CC, 35% GC, 7.5% SC, 7.5% BC%, 17.5% JN and 15% NT. No significant correlation was found between the treatments with different species ratio and water quality parameters. The final weight of different species, in different treatments, was statistically different. The major result was the clear positive effect on growth parameters observed by the introduction of JN and/or NT in to the carp polyculture. The yield per hectare was 2083.33±183 kg ha^?1 for polyculture with carp species; 2476.67±139.88 kg ha^?1 following the introduction of JN only; 2801.67±111.42 kg ha^?1 for isolated introduction of NT; and 2506.67±422.31 kg ha^?1 for simultaneous introduction of JN and NT. The introduction of JN and/or NT had a positive effect on growth parameters when compared with carp‐only polyculture. The reduction in CC ratio also had a positive effect on growth parameters.     

Effect of supplementation of dietary fibre concentrates on biochemical parameters,stress response,immune response and skin mucus of jundiá (Rhamdia quelen)

The aim of this study was to assess the effects of different dietary fibre concentrates (DFC: Mucilage = MG; pectin = PN or β‐glucan+mannan = βg+M), on biochemical parameters, stress and immune response and skin mucus of jundiá (Rhamdia quelen). The fish (7.16 ± 0.06 g) were fed with Control diet (0 g/kg of DFC); diet supplemented with 5 g/kg of commercial prebiotic (CP 5) or diets supplemented with 5 or 10 g/kg of MG; PN or βg+M. After 8 weeks of the feeding trials, biochemical parameters (cholesterol, glucose, albumin and total protein), cortisol, immunoglobulin IgM and mucoproteins of skin mucus were assessed. Results demonstrated that supplementation with PN increased cholesterol levels (p<.05). After application of the stressor, most fish, except those in the PN and 10 g/kg MG groups, showed significant increases (p<.05) in cholesterol, glucose and albumin levels. The jundiás showed no difference in cortisol levels after application of the stressor (p>.05). IgM levels were significantly high in fish supplemented with DFC (p<.05). However, the concentration of mucoproteins in skin mucus was not influenced in the different treatments (p>.05). The results showed that supplementation with DFC promoted beneficial effects on the metabolism of jundiá.     

Evaluation of immune response and performance of silver catfish fed functional linseed fibres in response to hypoxia stress

This study was conducted to evaluate the immunostimulating activity and growth promoting of diets supplemented with different rations of soluble and insoluble linseed fibre to Rhamdia quelen under hypoxia‐induced acute stress. For this reason, soluble and insoluble fractions of linseed fibre were concentrated separately and combined into four ratios (1:0.5; 1:1; 1:2 and 1:4), which were added to the diets of silver catfish (6.43 ± 0.12 g) and evaluated in a biological assay, along with a control diet (without addition of linseed fibre). After being fed the experimental diets for 45 days, specimens of silver catfish were submitted to hypoxia‐induced acute stress. They were kept out of water for 60 s. Immediately afterwards, blood and cutaneous mucus were collected for subsequent determination of immunological indicators and stress. After stress, the fish were weighed and measured for performance parameter calculation. The experimental design was completely randomized with five treatments and four replications. The data underwent analysis of variance and the means were compared by Tukey's test (p < .05). The fish fed diets containing the 1:2 and 1:4 soluble:insoluble fibre ratios, showed higher total protein content, globulin, plasma alkaline phosphatase activity, and performance in addition to higher mucoprotein content in the cutaneous mucus of the fish. Regardless of their ratio in the diet, linseed fibre provided higher plasma levels of total immunoglobulins and reduction in cortisol levels. The 1:1, 1:2 and 1:4 diets led to higher levels of total immunoglobulins and alkaline phosphatase activity in cutaneous mucus. The results indicate that linseed fibre has a stress‐ reduction, immunostimulant and a growth promoter effect on silver catfish. The 1:2 or 1:4 soluble: insoluble fibre ratios provided greater stimulation of the target immunological indicators and performance.     

Changes in skin colour and cortisol response of Australian snapper Pagrus auratus (Bloch & Schneider, 1801) to different background colours

A two-factor experiment was carried out to investigate the change in skin colour and plasma cortisol response of cultured Australian snapper Pagrus auratus to a change in background colour. Snapper (mean weight=437 g) were held in black or white tanks and fed diets containing 39 mg unesterified astaxanthin kg⁻¹ for 49 days before being transferred from white tanks to black cages (WB) or black tanks to white cages (BW). Skin colour values [ L ^* (lightness), a ^* (redness) and b ^* (yellowness)] of all snapper were measured at stocking ( t =0 days) and from cages of fish randomly assigned to each sampling time at 0.25, 0.5, 1, 2, 3, 5 and 7 days. Plasma cortisol was measured in anaesthetized snapper following colour measurements at 0, 1 and 7 days. Fish from additional black-to-black (BB) and white-to-white (WW) control treatments were also sampled for colour and cortisol at those times. Rapid changes occurred in skin lightness ( L ^* values) after altering background colour with maximum change in L ^* values for BW and WB treatments occurring within 1 day. Skin redness ( a ^*) of BW snapper continued to steadily decrease over the 7 days ( a ^*=7.93 × e^{−0.051 × time}). Plasma cortisol concentrations were highest at stocking when fish were held at greater densities and were not affected by cage colour. The results of this study suggest that transferring dark coloured snapper to white cages for 1 day is sufficient to affect the greatest benefit in terms of producing light coloured fish while minimizing the reduction in favourable red skin colouration.     

Modulation of the response of rainbow trout (Oncorhynchus mykiss Walbaum) to confinement, by an ectoparasitic (Argulus foliaceus L.) infestation and cortisol feeding

The effects of a 21 day infestation with the ectoparasite Argulus foliaceus on the response of rainbow trout Oncorhynchus mykiss to an acute stressor (confinement) were investigated. Fish were divided into a control and two parasitized groups, with one parasitized group having received cortisol feeding 72 and 24 h before infection. Prior to confinement only control fish showed a significant increase in body mass and condition factor. Following 4 h confinement, plasma glucose levels in the normal- fed/infested group were significantly higher than in the controls, while the cortisol-fed/infested group had significantly lower plasma levels of adrenocorticotropic hormone (ACTH) and glucose. Both infested groups, but not controls, had higher plasma ACTH and cortisol levels 48 h after confinement when compared with their pre-confinement levels. Stressor-induced immunomodulation was more evident in the parasitized fish after confinement, as was concluded from decreased lysozyme activity, alternative complement activity and oxygen radical production either immediately after, or 48 h post 4 h confinement. Circulating lymphocyte numbers were significantly reduced in the control and normal-fed/infested fish. Results indicate that low ectoparasitic infestations can, for a prolonged period, lead to a stress experience with effects that impair the response to subsequent stressors. Such effects may be further confounded by a previous elevation of plasma cortisol levels.     

Salt as a stress response mitigator of matrinxã, Brycon cephalus (Günther), during transport

The present study evaluated the physiological responses of matrinxã, Brycon cephalus (Günther) submitted to transport stress under the influence of sodium chloride. Different salt concentrations (0.0%, 0.1%, 0.3% and 0.6%) were added to four 200-L plastic tanks. Each tank was stocked with 30 fish (mean weight 1.0 ± 0.2 kg) and transported for 4 h. Blood was sampled prior to transport and immediately after and 24 and 96 h after transport. Plasma cortisol and glucose and serum sodium and potassium, plasma chloride and ammonia were analysed. Changes in plasma cortisol were observed immediately after transportation, except in fish transported in 0.3% and 0.6% salt. Twenty-four hours later, this hormone had returned to its initial level in all fish. Blood glucose was not changed in fish treated with 0.6% salt immediately after transport, and returned to the initial level within 96 h after the other treatments. All treatments resulted in lower levels of plasma chloride after transport, except for fish treated with 0.6% salt, with fish treated with 0.0% and 0.3% salt recovering 24 h later. Serum sodium decreased immediately after transport only in the control fish, returning to the initial level 24 h later. The results indicate that treatment with 0.6% NaCl reduces most of the physiological responses of matrinxã to the stress of transport.     

Stimulation of growth performance without causing stress response in young red sea bream, Pagrus major (Temminck & Schlegel), by photoperiod manipulation

Three photoperiods (12L:12D, 16L:8D and 24L:0D) were used to investigate the growth performance and stress response in red sea bream, Pagrus major (body weight 200–400 g). Fish were fed a commercial diet to apparent satiation, two times a day for 8 weeks. Fish exposed to a 24L:0D photoperiod showed a significantly higher weight gain (%) than those exposed to other photoperiods (P<0.05). The best specific growth rate and feed conversion efficiency were achieved at 24L:0D and 16L:8D, without significant differences among them. Although fish exposed to 16L:8D showed a significantly higher plasma level of cortisol than those exposed to other photoperiods in the third week, there was no major variation in the cortisol level among the treatments either at the sixth week or at the end of this study. There were no significant differences either in the haematocrit level or the plasma levels of glucose, total cholesterol and total protein among the treatments during this study. The results revealed that the growth performance of red sea bream reared from 200 to 400 g can be stimulated significantly using a continuous (24L:0D) photoperiod without any measurable significant stress response in fish.     

Growth,immune response and resistance to Aeromonas hydrophila of darkbarbel catfish,Pelteobagrus vachelli (Richardson), fed diets with different linolenic acid levels

Experimental diets were formulated containing six levels of linolenic acid (0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5%) and each diet was fed to darkbarbel catfish Pelteobagrus vachelli in triplicate for 84 days. Weight gain, specific growth rate and feed efficiency increased with the increasing levels of dietary linolenic acid, but were not significantly different among diets containing 1.0%, 1.5%, 2.0% and 2.5% linolenic acid. Red blood cell count and haemoglobin were significantly higher in fish fed the 1.0% linolenic acid than other diets. Lysozyme activity and immunoglobulin M content in fish fed 1.0% of linolenic acid were significantly higher compared with the other diets. Antibody titre in fish fed 1.0–2.5% linolenic acids was significantly higher than in fish fed 0 or 0.5% linolenic acid 14 days after Aeromonas hydrophila challenge. This study indicates that linolenic acid is essential to darkbarbel catfish. Two‐straight broken‐line analysis with SGR showed that a dietary level of 1.29% linolenic acid is the minimum required for adequate growth of darkbarbel catfish. Considering other measured indicators of fish performance, a level of 1.0–1.5% linolenic acid in the diet is recommended for the darkbarbel catfish.     

Stress response of Salmo salar (Linnaeus 1758) facing low abundance infestation of Caligus rogercresseyi (Boxshall & Bravo 2000), an object in the tank,and handling

This study looks at how low infestation loads of adult Caligus rogercresseyi and other stressors affect the physiology of Salmo salar. Experimental fish groups were with (infested) or without (control) exposure to the parasite. The parasite cohort was followed for 78 days post‐infestation (dpi), and only adult lice were observed. Additional stressors were applied at 60 and 75 dpi. The analysis included measurements of fish physiology and weight. Low‐level infestations by adult C. rogercresseyi for more than 50 dpi induced moderate stress in S. salar as well as a high energy demand and increased small skin mucous cells. Threshold lice loads were identified, and above those loads, a high stress response was observed. Additional stressors altered fish physiology, inducing downregulation of the cortisol response after the first stressor and upregulation after the second stressor, but infested fish responded more strongly. Parasitism by C. rogercresseyi is energetically demanding, affecting the primary and secondary responses (e.g. cortisol and glucose levels), as well as the tertiary response (fish weight).     

Hypoxia‐induced changes in survival,immune response and antioxidant status of the Pacific white shrimp (Litopenaeus vannamei) fed with graded levels of dietary myo‐inositol

A 3‐hr experiment was conducted to investigate the effects of dietary myo‐inositol (MI) supplementation on survival, immune response and antioxidant abilities in Litopenaeus vannamei under acute hypoxia stress. Six practical diets were formulated with supplementation of graded levels (control group 0, 0.1, 0.2, 0.4, 0.8 and 1.6 g/kg dry diet) of MI and were randomly assigned to triplicate groups of L. vannamei (mean weight 0.40 ± 0.00 g) for 8 weeks. Ten healthy shrimp (final mean weight approximately 11–14 g) randomly selected from each tank were exposed to hypoxia stress after feeding trial. After 3‐hr acute hypoxia stress, survival of shrimp fed MI‐supplemented diets (except 0.1 and 0.4 g/kg diets) was significantly increased compared with the control group. Shrimp fed control diet had lower activities of alkaline phosphatase (AKP), acid phosphatase (ACP), total antioxidant capacity (T‐AOC) and glutathione peroxidase (GPX), and higher malondialdehyde (MDA) and protein carbonyl (PC) contents in hepatopancreas than those fed the MI‐supplemented diets. In addition, mRNA expression levels of heat shock protein 70 (Hsp70), catalase (CAT) and penaeidin were significantly differentially regulated in hepatopancreas. In summary, dietary MI supplementation may have a positive effect on improving resistance to acute hypoxia stress of L. vannamei.     

Effects of l‐tryptophan on the performance,energy partitioning and endocrine response of Japanese sea cucumber (Apostichopus japonicus Selenka) exposed to crowding stress

The effects of dietary tryptophan on growth performance, energy budget and endocrine response of sea cucumber Apostichopus japonicus (Selenka) were studied, to test whether the tryptophan could mitigate the crowding stress response of the sea cucumber. Four density treatments of the sea cucumber (i.e. 4, 8, 16 and 32 individuals per 40 L water, represented as L, ML, MH and H) were fed with diets containing 0 (control), 1%, 3% and 5% l ‐tryptophan, respectively, for 75 days. The results showed that the specific growth rate (SGR) and feed conversion ratio (FCE) of A. japonicus decreased with increasing in the stocking densities but increased after supplementation of 1% and 3% tryptophan. The energy allocation of the A. japonicus was affected significantly by stocking density and dietary tryptophan treatments (p < .05). In general, the energy consumed (C) and energy used for growth (G) decreased with the increasing in the stocking densities. The highest proportion of energy deposited to growth occurred in each 3% treatment (L, 6.38%; ML, 6.12%; MH, 4.56% and H, 4.14%), which were significantly higher than the controls (p < .05) respectively. Higher cortisol, glucose and lactate levels of A. japonicus were recorded in the control treatments of MH and H, but l ‐tryptophan supplementation could reduce the levels of cortisol, glucose and lactate of the test animals. The present results proved that the growth performance of the sea cucumber was inhibited by high stocking densities, while dietary supplementation of tryptophan could significantly mitigate the crowding stress, and improve the growth of sea cucumber.