Feeding interval and photoperiod influence the growth performance of striped knifejaw,Oplegnathus fasciatus

A two‐factor experiment incorporating two photoperiods (16 L:8 D and 24 L:0 D) and four feeding intervals (6, 9, 12 and 24 h) was carried out to determine the most efficient feeding interval and photoperiod for striped knifejaw, Oplegnathus fasciatus. Fish were fed a commercial diet to apparent satiation for 10 weeks. Blood was collected to measure the stress indicators. Both the photoperiod and the feeding intervals had a significant effect on the growth performance of striped knifejaw; however, their interaction did not produce any significant effect. The final body weight, weight gain (%) and feed intake at 6‐, 9‐ and 12‐h feeding intervals under 16 L:8 D were significantly higher than those at the 24‐h interval irrespective of the photoperiod (P<0.05). The specific growth rate at 6, 9 and 12 h intervals of the 16 L:8 D photoperiod was significantly higher than that of the other feeding intervals, except at 12 h of the 24 L:0 D photoperiod (P<0.05). At the end of the experiment, there were no significant differences in the plasma levels of cortisol, glucose and total protein observed in fish exposed to different photoperiods compared with the initial levels. The results suggested that a combination of a 16 L:8 D photoperiod and either of 6‐, 9‐ or 12‐h intervals can be used to stimulate the growth performance in striped knifejaw.     

Partial substitution of dietary fish meal with soybean meal for speckled shrimp,Metapenaeus monoceros (Fabricius, 1798) (Decapoda: Penaeidae) juvenile

A 63‐day feeding study was conducted to evaluate the effect of partial substitution (0%, 20%, 40% and 60%) of dietary fish meal (FM) with soybean meal (SBM) on the growth performance and feed utilization of speckled shrimp, Metapenaeus monoceros juveniles. A total of 180 M. monoceros juveniles with an average weight of 0.67 ± 0.18 g were equally distributed over 12 glass aquaria (30 L each, triplicate per treatment). All aquaria were filled with filtered sea water (30–35 ‰, salinity). Four isonitrogenous (400 g kg^?1 crude protein) and isocaloric (20.5 MJ GE kg^?1) test diets were formulated. The control diet contained FM (D₁) as the main protein source. In the other diets, FM was partially replaced with 20 (D₂), 40% (D₃) or 60% (D₄) SBM. The results indicate that the diet in which 40% of the FM is replaced by SBM yields similar growth and production, and is as cost effective, as the control diet.     

Growth performance and physiological responses in striped knifejaw, Oplegnathus fasciatus, held under different photoperiods

The growth performance and stress response in striped knifejaw, Oplegnathus fasciatus (body weight 100–300 g) reared under four photoperiods (6L:6D, 12L:12D, 16L:8D and 24L:0D) were investigated. Fish were fed a commercial diet to apparent satiation, two times a day for 8 weeks. A trial of acute handling and confinement stress was also carried out to investigate the stress-induced levels of different stress indicators in O. fasciatus. Blood was also collected from undisturbed fish which was considered as control. Although there were no significant differences in weight gain, specific growth rate (SGR) and feed conversion efficiency (FCE) in fish exposed to 6L:6D, 16L:8D and 24L:0D photoperiods, all parameters in these photoperiods were significantly higher than those of 12L:12D photoperiod (P < 0.05). There was no significant difference in protein retention efficiency (PRE) between fish exposed to 16L:8D and 24L:0D photoperiods, but PRE in both photoperiods was significantly higher than that of 12L:12D photoperiod.Acute stress significantly increased the plasma levels of cortisol (110.3 ng ml^− 1) and glucose (195.4 mg dl^− 1), and decreased plasma levels of total protein (0.8 g dl^− 1); however, all parameters were returned back to the levels indistinguishable from those of control, undisturbed fish within 24 h. The levels of cortisol, glucose and total protein in fish exposed to different photoperiods during the study were far from the stress-induced levels (P < 0.05). The results demonstrated that the growth performance of O. fasciatus reared from 100 to 300 g can be stimulated significantly by using the manipulated photoperiods where feeding time may be playing an important role to increase food intake and feed conversion efficiency. It also revealed that the artificial photoperiods did not cause significant stress response in fish.     

Dietary utility of enzyme-treated fish meal for juvenile Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis>

ABSTRACT:   In order to develop an artificial diet, the dietary utility of enzyme-treated fish meal was investigated for juvenile Pacific bluefin tuna Thunnus orientalis (PBT). Diets containing each 63% of Chilean fish meal (FM), enzyme-treated Chilean fish meal (EC) and enzyme-treated Peruvian fish meal (EP), with 10% bonito oil and raw sand lance Ammodytes personatus (SL) were fed to juvenile tuna six times per day for one week. In a different trial, diets EC and SL were fed to tuna six times per day for 2 weeks. Only diet EC sustained similar growth or caused lower survival and higher feed efficiency, hepato- and enterosomatic indices and final carcass lipid content as compared to those of SL. Diets FM and EP led to lower specific growth rate (SGR) but similar feed efficiency, survival and hepatosomatic index, yet higher enterosomatic index. Moreover, PBT fed diet EC for 2 weeks led to similar growth performance but higher final carcass and hepatic lipid contents, and plasma cholesterol and phospholipid levels than those fed SL. Carcass fatty acid composition of diet EC group had lower 20:5  n -3 and 22:6  n -3 levels than the SL group. These results revealed that EC, as a suitable dietary protein source, could sustain growth of PBT, while dietary bonito oil led to higher carcass lipid but lower accumulation of n -3 highly unsaturated fatty acids.     

Response of plant yield and leaf pigments to saline conditions: Effectiveness of different rootstocks in melon plants (Cucumis melo L.)

Two varieties of Cucumis melo (Resisto and Arava) were grafted onto three hybrids of Cucurbita maxima and Cucurbita moschata cultivars (Shintoza, RS-841 and Kamel). Ungrafted Cucumis melo var. Resisto and var. Arava plants were used as controls. Plants were grown under controlled greenhouse conditions and were constantly fertilized with macro- and micronutrients, supplied with irrigation water rich in Na⁺ and Cl^- Contents of chlorophylls a and b, carotene pigments, Cl^- and total and soluble Na⁺ and K⁺ ions were measured in all the scion parts of the plants. The results showed that grafted plants exhibited differences in the leaf content of Na+ and especially Cl^- in comparison with ungrafted plants. In addition, yield as well as leaf pigments appeared to be good indicators of Cl^- levels in scion parts. It is assumed that grafted plants developed various mechanisms to avoid physiological damage caused by the excessive accumulation of these ions in leaf, including the exclusion of Cl^- ion and/or decrease in Cl^- absorption by the roots and the replacement or substitution of total K⁺ by total Na⁺ in the foliar parts.     

Effects of Light Intensity on the Growth Performance and Stress Response in Striped Knifejaw, (Oplegnathus fasciatus)

Six light intensities (50, 100, 200, 400, 800, and 1500 lx) were used under a photoperiod of 16 h light : 8 h dark (16L : 8D) to investigate the growth performance and stress response of striped knifejaw, Oplegnathus fasciatus. Forty juveniles of mean weight approximately 27 g were randomly distributed into each of eighteen 300 L tanks, fed to apparent satiation two times a day for 8 wk. At the end of the rearing trial, there were no significant differences in final mean weight, weight gain, specific growth rate, condition factor, and survival among the treatments (P > 0.05). Although there was no significant difference in feed intake, fish exposed to 50–200 lx showed significantly higher feed efficiency (FE) compared to that of other treatments (P < 0.05). There was a decreasing trend in retention efficiency of protein and lipid with increasing light intensities (400–1500 lx), but there were no significant differences among the treatments. There were no significant differences in plasma levels of cortisol, glucose, and total protein among the treatments (P > 0.05). To consider the FE and given the fact that an intensity of 50 lx is insufficient to monitor fish activity during feeding, light intensity of 100–200 lx would be better for rearing of striped knifejaw.     

Effect of Artemia enrichment on the growth and survival of Pacific bluefin tuna Thunnus orientalis (Temminck & Schlegel) larvae

This study was carried out to investigate the suitability of Artemia enriched with docosahexaenoic acid (DHA) and choline as live food on the growth and survival rate of the Pacific bluefin tuna (PBT; Thunnus orientalis) larvae. The PBT larvae were fed either Artemia enriched with oleic acid (Diet 1), DHA (Diet 2), DHA+choline 1.0 mg L^?1 (Diet 3) and DHA+choline 2.0 mg L^?1 (Diet 4) or striped knifejaw larvae (Diet 5, reference diet), in duplicate for 12 days. Enrichment of Artemia with DHA significantly increased the DHA levels to 13.9, 13.8 and 12.5 mg g^?1 on a dry matter basis in Diets 2, 3 and 4 respectively; however, the levels were significantly lower than the reference diet (26.9 mg g^?1 dry matter basis; Diet 5). Although growth and survival rate were significantly improved by the enrichment of Artemia with DHA and choline, the improvement was negligible compared with the enhanced growth and survival rate of the fish larvae‐fed group (P<0.05). The results demonstrated that enriched Artemia does not seem to be the right choice to feed the PBT larvae perhaps because of the difficulties in achieving the correct balance of fatty acid with higher DHA/EPA from Artemia nauplii.