Bioavailability of selenium from different dietary sources in yellowtail kingfish (Seriola lalandi)

Different forms of selenium (Se) were supplemented to a fishmeal-based diet to investigate the digestibility and bioavailability of Se in yellowtail kingfish (Seriola lalandi). Five groups of fish in triplicate were fed a basal diet (containing 3.31 mg/kg Se) either unsupplemented or supplemented with 2 mg/kg Se from selenite, selenocystine (SeCys), selenomethionine (SeMet) or Se-yeast for 6 weeks. The basal unsupplemented diet resulted in significantly lower weight gain, red blood cell glutathione peroxidase (GPx) and bactericidal activities than the supplemented diets. Muscle Se concentration was increased by Se supplementation from SeCys, SeMet or Se-yeast, but not selenite. There was no difference in GPx activity of fish fed with any supplemented diets. The bioavailability of Se from SeMet and Se-yeast was similar for all measurements. The most digestible sources of Se were from SeMet and Se-yeast, whereas the least was from fishmeal. Se from SeMet or Se-yeast produced more weight gain, higher Se accumulation in muscle tissues and bactericidal activity in yellowtail kingfish than Se from SeCys or selenite. This study shows that SeMet and Se-yeast are the most bioavailable sources of Se to yellowtail kingfish and are recommended to be supplemented to fishmeal-based formulated diets for yellowtail kingfish

Toxic effects of excessive levels of dietary selenium in juvenile yellowtail kingfish (Seriola lalandi)

Selenomethionine (SeMet) was supplemented to a fishmeal-based diet to investigate the toxic effects of excessive levels of dietary selenium (Se) in juvenile yellowtail kingfish (Seriola lalandi). For 10 weeks, the fish were fed one of five experimental diets; a basal diet containing 2.31 mg/kg of inherent Se or diets supplemented with SeMet to provide 4.91, 9.58, 15.43 or 20.87 mg/kg of Se. The results showed that the fish muscle proximate composition, feed conversion ratio and survival were not sensitive to dietary Se treatments; and no histopathological lesions were observed in heart and intestine tissues of the fish. The Se concentrations in liver and muscle tissues showed a strong linear positive relationship with the levels of Se in diets. Fish when fed the basal diet exhibited Se deficiency symptoms including myopathy, reduced feed intake, glutathione peroxidase activity and growth; whereas those fed the diets containing ≥ 4.91 mg Se/kg did not. While fish fed the 15.43 mg Se/kg diet did not show any toxic effects, the 20.87 mg Se/kg diet caused histopathological changes in liver and spleen as well as reduced feed intake, growth, haematocrit and hepatosomatic index, indicating Se toxicity. In conclusion, Se levels in liver and muscle tissues can be used as effective indicators of dietary Se exposure and dietary Se level between 15.43 and 20.87 mg/kg may be a threshold level in juvenile yellowtail kingfish

REPRODUCTIVE PERFORMANCE OF DOMESTICATED BROODSTOCK OF SILVER PERCH, Bidyanus bidyanus (MITCHELL 1838) AND THE RELATIONSHIP BETWEEN OIL GLOBULE FRAGMENTATION AND EGG QUALITY

The experiments investigated the reproductive performance of the domesticated broodstock of the silver perch and the relationship between various degrees of oil globule fragmentation and egg quality. Six years old of second generation broodstock (n=3) were evaluated based on the fecundity, fertilisation rate, hatching rate, the degree of oil fragmentation of egg, and the quality of embryos and larvae produced. The fragmentation were grouped into three categories: un-fragmented (cat-1), moderately fragmented (cat-2), and highly fragmented (cat-3). The results showed that the broodstock had a relatively high fecundity (132,400 ± 7,22), fertilization rate (94.27 ± 1.28%), and hatching rates (87.94 ± 1.23%). The survival rate of larvae at 12 days post hatching (dph) in cat-1 (71.3 ± 0.9%) was higher than cat-2 (66.7 ± 0.9%) whereas cat-2 was higher than cat-3 (61.3 ± 0.3%). The eggs was dominated by cat-1 (78.11 ± 2.44%) which was significantly higher than cat-2 (21.26 ± 2.45%) and cat-3 ones (0.40 ± 0.21%). The survival rate of embryo at 20 hours post spawning (hps) and hatching rate of cat-1 (95.33 ± 0.00% and 93.33 ± 0.00%) and cat-2 (90.00 ± 0.00% and 85.00 ± 0.00%) were significantly higher than cat-3 (72.33 ± 1.76% and 60.33 ± 0.00%). The total length (TL) of the larvae of cat-1 and cat-2 (8.44 ± 0.21 mm and 8.35 ± 0.23 mm respectively) were significantly higher than larvae of cat-3 (7.09 ± 0.14 mm). No significant difference was found in the larval deformities among any categories. In conclusion, the reproductive performance of six year-old broodstock silver perch showing acceptable performance and egg categorisation based on oil globule fragmentation can be used as a useful tool to indicate eggs quality of silver perch

Early development of the blue mussel Mytilus edulis (Linnaeus, 1758) cultured in potassium-fortified inland saline water

The low potassium concentration in inland saline water (ISW) restrains the normal development of cultured marine organisms, and thus, possesses challenges for the development of ISW aquaculture. Therefore, assessing the effects of potassium fortification in ISW on the performance of cultured marine species is an important step to determine the feasibility of their culture in ISW. The aim of this research was to investigate the effects of potassium fortification in ISW on the performance of early life stages of the blue mussel Mytilus edulis including fertilised eggs, trochophore, veliger and pediveliger larvae. These stages were reared in five different levels of potassium-fortified ISW, namely 20, 40, 60, 80 and 100% of potassium levels equivalent to the potassium level in ocean water (OW) and two controls namely, ISW at 27 ppt (ISW27) and OW at 25 ppt (OW25). The results showed that the higher levels of potassium in ISW, particularly with 100% K+ fortification (ISW100K+), invariably improved the survival and size, and reduced the developmental stage interval and deformities of blue mussel larvae. Deformities, such as faulty cell cleavage, abnormal formation of trochophore larvae, protruding mantle in veliger larvae, and indented shell margin in veliger and in pediveliger, were observed when reared in any ISW. However, rearing in ISW did not result in any deformities in settlement larvae. The number of deformities was reduced at higher K+ fortification levels, and there were no deformities in pediveliger larvae reared in ISW100K+ and in OW. These results showed that K+ fortification in ISW improves the performance of the rearing of the larval stages of the blue mussel. Statement of relevance: This study is the first attempt to culture larval stages of blue mussel Mytilus edulis in potassium-fortified inland saline water. The results have shown that that the larval development is feasible only if ISW is fortified with K+. By initiating larval culture in inland saline water, we expect better results will be reflected by adult stages

Growth, survival and physiological condition of cultured marron, Cherax tenuimanus (Smith, 1912) fed different levels of organic selenium

A 90-day feeding experiment was conducted to evaluate the effects of three levels of dietary supplementation of organic selenium (OS) on physiological and immunological responses of marron (Cherax tenuimanus). Three levels viz. 0.1, 0.2 and 0.3 g kg-1 of basal diet of Sel-Plex® as a source of OS. were prepared and tested against the basal diet, which was used as a control. Each diet was fed to four replicated groups of marron, (initial mean weight of 39.43 ± 0.55 g), at a rate of 3% body weight every second day. At the end of the feeding experiment, dietary inclusion of all Sel-Plex® levels significantly improved specific growth rate (SGR) and survival of marron. Inclusion of Sel-Plex® above 0.1 g kg-1 resulted in significantly higher hepatopancreatic moisture level (HM) and wet hepatosomatic index (Hiw), of marron than marron fed without Sel-Plex. Total Se level in the hepatopancreas was thehighest (5.41 ± 0.28 ?g g-1) in the marron fed 0.2 g kg-1 of Sel-Plex, whereas muscle accumulated significantly higher level of Se when marron were fed 0.3 g kg-1 of dietary Sel-Plex. It is therefore suggested that the beneficial dietary supplementation levels of Sel-Plex in marron should range from 0.2 to 0.3 g kg-1

Dietary organic selenium improves growth, survival and resistance to vibrio mimicus in cultured marron, cherax cainii (Austin, 2002)

To determine the effects of dietary organic selenium (OS) supplementation on the growth performance and immune competence of marron, Cherax cainii (Austin, 2002), a group of marron were fed 0.2 g kg−1 of Sel-Plex® supplemented basal diet and then compared with another group (control) of marron fed basal diet without any supplementation. After 90 days of feeding, final weight, average weekly gains (AWG), relative gain rate (RGR), specific growth rate (SGR), survival, total and differential haemocyte counts (THC and DHC), were compared between the two groups. Surviving marron from each group were then divided into three sub-groups (three tanks per sub-group with seven marron per tank); (1) first sub-group was injected with 20 μL of 3.24 × 106 cfu Vibrio mimicus; (2) the second sub-group was injected with 20 μL normal saline and (3) the third sub-group was not subjected to injection and became the control group. THC, DHC, neutral red retention time (NRRT) and Vibrio ranks of post-injected marron were evaluated for 96 h, at every 24-h interval.The results showed that after 90 days of feeding, final weight, AWG, RGR, SGR, survival, THC, proportion of hyaline cells of OS-fed marron were significantly higher (P<0.05) than the control group, whereas proportion of granular and semigranular cells were not affected by dietary OS. After challenging with V. mimicus, survival rate of marron without dietary OS significantly decreased (P<0.05) as compared to the control group of marron. THC of marron in all sub-groups were significantly reduced (P<0.05) after the challenge. However, THC and granular cells of sub-groups fed OS were higher than other sub-groups. Vibrio ranks and NRRT of marron fed OS were significantly lower and slower, respectively, than marron fed without OS. These findings demonstrated the benefits of OS inclusion in the marron diet in terms of growth, health and disease resistance

Dietary selenium requirement of yellowtail kingfish (Seriola lalandi)

The dietary selenium (Se) requirement of yellowtail kingfish (Seriola lalandi) in normal and infected conditions was investigated. The fish were fed one of five experimental diets; a control un-supplemented diet (3.35 mg/kg Se) or diets supplemented with Se to provide 4.86, 5.38, 5.85 or 6.38 mg/kg Se. After feeding for 6 weeks, the fish were challenged by Vibrio anguillarum immersion and then observed for 4 weeks. Supplementation of Se had no effect on feed intake, feed conversion ratio and survival over 6 weeks of feeding; however, it significantly increased growth and Se content in muscle tissues. The optimal Se level for maximal growth of yellowtail kingfish estimated by second order regression was 5.56 mg/kg. Following the bacterial challenge, the immune-stimulating effects of Se were demonstrated in lysozyme and bactericidal activities, and there was a corresponding increase in survival and antibody response by supplementation of Se at ≥2 mg/kg (measured Se of ≥5.38 mg/kg). Under normal and infectious conditions, antioxidant capacity of fish measured as glutathione peroxidase activity increased by supplementation of Se. During post-challenge period, haematocrits were higher in the fish fed Se supplemented diets than the fish fed the control diet, while more macrophage aggregates were seen in the control group than in the others. Furthermore, there was evidence of myopathy in fish fed the diet without Se supplementation. Therefore, the results indicated that the optimal dietary Se requirement of yellowtail kingfish is 5.56 mg/kg

Evaluation of Sargassum sp. as a nutrient-sink in an integrated seaweed-prawn (ISP) culture system

Effluent water from intensive prawn aquaculture systems typically has a high concentration of dissolved nutrients such as nitrogen and phosphorus. A study was conducted for 42 days to investigate the nutrient flow in a system where brown seaweed (Sargassum sp.) was integrated into western king prawn (Penaeus latisulcatus) culture. Three treatments namely, western king prawn monoculture (5.48 ± 0.29 g), Sargassum sp. monoculture and seaweed/prawn integrated culture were tested for nutrient flow among feed, water and species cultured. The results showed that by integrating seaweed into prawn culture, the concentrations of total ammonium nitrogen (TAN), nitrite–nitrogen (NO2−) and nitrate–nitrogen (NO3−), dissolved inorganic nitrogen (DIN), total nitrogen (TN), phosphate (PO43−) and total phosphorus (TP) were significantly lower (p 0.05) from the prawn monoculture. The mean biomass of Sargassum sp. in integrated culture increased at the rate of 3.16 ± 0.74% g day−1 after 7 days of the study, which was significantly higher than in the monoculture system (5.70 ± 0.82% g day−1). The results suggest that integrating Sargassum sp. into western king prawn culture can benefit prawn farming by assisting in the maintenance of optimum water quality and thereby, reducing environmental impacts on surrounding areas

Removal of Inorganic Nitrogen by Integrating Seaweed (Sargassum sp.) into Western King Prawn (Penaeus latisulcatus, Kishinouye 1896) Culture

Effluent water from intensive prawn culture ponds typically has high concentrations of dissolved nutrients such as nitrogen. An experiment was conducted for 28 days to investigate the nitrogen flow where seaweed (Sargassum sp.) was integrated into western king prawn (Penaeus latisulcatus) culture. Three treatments were used, each consisting of four, 0.1m3 plastic tanks. Treatment 1 and 2 were the monocultures of western king prawns (5.48 ± 0.29 g) and seaweed (young seaweed). Treatment 3 was an integrated culture of prawns and seaweed. Five prawns were stocked in each tank of treatment 1 and 3. About 137 ± 0.36 g of biomass seaweed was stocked in the treatment 2 and 3. Prawns in prawn monoculture and integrated culture were fed twice a day at a rate of 2.5% of total body weight. The concentration of dissolved inorganic nitrogen (DIN) discharged from the prawn monoculture increased from 0.126 to 10.98 mg/L during the experiment. The concentration of total ammonium nitrogen (TAN), nitrite-nitrogen (NO2-) and nitrate-nitrogen (NO3-) in the integrated culture was significantly lower at the termination of the experiment than the prawn monoculture (p≤0.05). The concentration of TAN, NO2-, NO3- and DIN in the integrated culture remained within non-toxic limits for the duration of the experiment. Integrating Sargassum sp. with prawns did not alter the specific growth rate (SGR) and survival rate of the prawns (p>0.05). The mean biomass of seaweed in the integrated culture increased at the rate of 3.16 ± 0.74% g per day after 7 days of the experiment, which was significantly lower (p≤0.05) than the growth rate of the seaweed in the monoculture (5.70 ± 0.82 % g per day). The results suggest that integrating seaweed into prawn culture can benefit prawn farming by assisting in the maintenance of optimum water quality and thereby, reduce environmental impacts on surrounding areas

Effect of Customized Probiotics on the Physiological and Immunological Responses of Juvenile Western King Prawns (Penaeus latisulcatus Kishinouye, 1896) Challenged with Vibrio harveyi

Juvenile western king prawn P. latisulcatus were fed 105 colony-forming units (CFU)/mL of two probiotics Pseudomonas synxantha and P. aeruginosa for 28 days. P. latisulcatus were then challenged with V. harveyi at 0 (control), 103, 105, and 107 CFU/mL. During the seven days of challenge, disease resistance of the probiotic-fed prawns was compared with that of prawns not fed probiotics. The immunological responses of the prawns did not improve during the challenge period in terms of total haemocyte count, hyalinocyte, semi-ganulocyte, granulocyte, clotting time, bacteraemia, and intestinal bacterial load. Overall, when prawns were challenged with V. harveyi, the LT50 values got shorter as V. harveyi concentration increased. LT50 values of prawns fed probiotics were significantly longer (P < 0.05) than those not fed probiotics. At a V. harveyi concentration of 103 CFU/mL, the 100% survival of the prawns fed probiotics was three times more likely than those of the prawns not fed probiotics