Dynamics of plasma free amino acids in rainbow trout (Oncorhynchus mykiss under variety of dietary conditions

Plasma amino acid profiles in the systemic circulation of rainbow trout acclimated to diets containing different protein sources, with and without supplementation with free amino acids, were monitored for up to 120 hours after consumption of the diets. Plasma concentrations of lysine, methionine, and isoleucine increased more rapidly after feeding a diet supplemented with these amino acids in free form and, depending upon the increase in plasma concentration, remained at concentrations above those in fish fed the basal diet for at least 24h after feeding. Dietary supplementation with isoleucine increased plasma concentrations of leucine and valine as well as of isoleucine. Maximum plasma concentrations for most amino acids were attained between 12 and 24h postprandial. Dietary inclusion of gelatin caused more rapid elevations in plasma glycine and serine than did free glycine. Feeding at three hour intervals resulted in stable plasma concentrations of individual amino acids in contrast to the fluctuations occurring when fish were fed once daily. Frequent feeding favoured a higher proportion of protein to lipid in body composition.     

Effects of various dietary factors on astaxanthin absorption in Atlantic salmon (Salmo salar)

The experiment was designed to investigate the dietary factors that might enhance or interfere with astaxanthin (Ax) absorption in salmon including potentially interfering factors such as certain carotenoids (zeaxanthin and lutein), plant sterols, fibre and enhancing compounds such as cholesterol and vitamin E. Two hundred and eighty‐eight salmon (778 ± 78 g) were reared in sea water under controlled conditions and fed practical experimental diets. The experimental diets were supplemented with 40 mg Ax kg^?1, in addition to various dietary factors, including cholesterol (2%), vitamin E (450 IU kg^?1), wheat bran (5%), lutein (40 mg kg^?1), zeaxanthin (40 mg kg^?1) and phytosterol (2%). After 26 days of feeding, blood was collected and plasma was separated to determine the plasma Ax concentration. Ax was not detected in the plasma of fish fed the non‐pigmented diet. Fish fed diet containing 2% cholesterol significantly improved Ax absorption, which was reflected in the higher Ax concentration in plasma of Atlantic salmon. Other supplements including vitamin E, wheat bran, lutein, zeaxanthin and phytosterols in diet had no significant effect on plasma Ax concentration . Fish fed diet containing 2% cholesterol significantly increased cholesterol concentration in fish plasma. Phytosterol had no benefit to lower cholesterol plasma level in fish fed 2% phytosterol‐supplemented diet.     

A new host record of Sphaerospora epinepheli (Myxosporea: Bivalvulida) occurring on orange-spotted grouper Epinephelus coioides from Thailand: epidemiology, histopathology and phylogenetic position

In 1991, the first record of Sphaerospora epinepheli was described as a kidney parasite of wild and cultured malabar grouper, Epinephelus malabaricus, along coastlines of Thailand, the Gulf of Thailand and the Andaman Sea. However, the present study detected high infection of this parasite in kidney renal tubes of orange spotted grouper, Epinephelus coioides, collected from Andaman Sea. The highest infection rate of 36.82% was observed during the rainy season in 2009 in Phang-Nga Bay, in the north of Andaman Sea, which is an important grouper production site in Thailand. The biological and histopathological data of the parasite in this new host record are presented. Species classification is described based on morphological data of mature spore and molecular analysis of myxosporean 18S rDNA phylogeny including that of S. epinepheli which infected E. malabaricus. The genetic position of this parasite found in two host species was also studied. The phylogenetic tree analysis of small-subunit rDNA sequences of S. epinepheli from both infected hosts was constructed using two algorithms, maximum likelihood (ML) and Bayesian inference (BI). They were placed in the clustered basal sphaerosporid clade that contain four long SSU rDNA sphaerosporid species including Sphaerospora truttae, Sphaerospora elegans, Sphaerospora ranae, Sphaerospora fugu and Bipteria formosa with strong bootstrap supports. Histopathologically, renal intratubular myxosporean spores were associated with tubulonephosis, tubular necrosis, chronic interstitial nephritis and mimic membranoproliferative glomerulonephritis. This myxosporean parasite appears to be a significant pathogen on the basis of pathological changes in the renal tubules and is highly distributed in orange-spotted grouper.     

Fungicidal activity of Thai medicinal plant extracts against <Emphasis Type="Italic">Alternaria brassicicola</Emphasis> causing black spot of Chinese kale

Crude ethanol extracts and six organic solvent fractions of 10 Thai medicinal plants were evaluated for their antifungal activity against Alternaria brassicicola in laboratory and under greenhouse conditions. The results showed that the ethanol extracts of Coscinium fenestratum, Piper betle, Syzygium aromaticus and Zingiber cassumunar displayed complete mycelial growth inhibition of A. brassicicola at a concentration of 0.1%. Meanwhile, the crude ethanol extract and methanol fraction obtained from the stems of C. fenestratum revealed the greatest inhibition against A. brassicicola at 10%, forming inhibition zones 2.55–2.58 cm in diameter. In the greenhouse experiments, crude ethanol extracts of C. fenestratum and P. betle at 1% significantly (P?<?0.05) reduced the disease incidence at up to 67%, indicating promising preventive and curative activities against A. brassicicola. This activity is similar to that of iprodione, a widely used commercial fungicide. Interestingly, Illicium verum extract showed a greater curative effect (58% disease reduction) than protective effect (47% disease reduction). Because the C. fenestratum extract showed the highest activity against the black spot pathogen both in vitro and under greenhouse conditions, its methanol fraction was further analyzed by spectroscopic techniques. We found that berberine is a key active substance inhibiting mycelial growth of A. brassicicola. The results of this study showed the potential of Thai medicinal plants as alternatives to the use of synthetic fungicides for controlling black spot in Chinese kale caused by A. brassicicola.     

Production of protein hydrolysates from skipjack tuna (Katsuwonus pelamis) viscera as feeding attractants for Asian seabass (Lates calcarifer)

Skipjack tuna viscera hydrolysate (TVH) was produced by enzymatic hydrolysis using alcalase. A study of the effect of time and enzyme concentration was performed and formed the basis for preparing TVH with the desired degree of hydrolysis (DH). An enzyme to substrate ratio of 5 g kg⁻¹ (TVH A1) and 16.4 g kg⁻¹ (TVH A2) at pH 8.0 with a temperature of 50 °C, and hydrolysis time of 60 min were found to be optimal conditions to obtain hydrolysis of 42.9% and 62.9%, respectively. Both TVH A1 and TVH A2 were analysed for chemical and amino acid composition and peptide size. The effectiveness of TVH at different DH as feeding attractants was estimated in a feeding trial at different inclusion levels. Ten experimental diets , including a fish meal‐based reference diet, were fed to Asian seabass for 28 days. Fish fed the diet supplemented with 30 g kg⁻¹ of TVH A2, and the reference diet showed the highest feed intake (P < 0.05). The growth performance of fish fed diets supplemented with TVH was slightly higher than those of fish fed the control diet, but the reference group showed a significantly higher growth rate (P < 0.05). These findings suggest that the supplementation of feed with TVH that has been processed under suitable conditions can improve feed palatability and growth performance when utilizing alternative protein sources in Asian seabass diets.     

Molecular isolation and characterization of a haemocyanin of Macrobrachium rosenbergii reveal its antibacterial activities

Haemocyanin is a multi‐subunit protein complex found in the haemolymph and is involved in the immune system of crustaceans. In this study, a haemocyanin gene of Macrobrachium rosenbergii, designated MrHc, was successfully isolated. The MrHc gene contained an open reading frame (ORF) of 1,992 nucleotides, encoding a protein of 663 amino acid residues with a molecular mass of 76.5 kDa. The deduced amino acid sequence contained distinct structural motifs of the haemocyanin superfamily, including an all‐alpha domain, a copper‐containing domain and an immunoglobulin‐like domain. Based on the phylogenetic analysis, the MrHC protein demonstrated a close relationship with the haemocyanins of Palaemon carinicauda and Macrobrachium nipponense. The MrHc gene was expressed in various shrimp tissues, including the hepatopancreas, gill, haemocytes, stomach and muscle. After Macrobrachium rosenbergii nodavirus (MrNV) challenge tests, the MrHc gene was up‐regulated 237‐fold at day 2. A recombinant protein of the MrHc immunoglobulin‐like domain exhibited antibacterial activity against Vibrio vulnificus, V. parahaemolyticus, Aeromonas caviae, A. veronii, A. hydrophila and Bacillus cereus. This study suggested that MrHc may play important roles in the shrimp innate immune response to MrNV infection and bacterial infection.