The phenomenon of mass mortality of larval mud crab Scylla serrata is described during the metamorphosis to megalops due to abnormal molting by morphologically advanced last stage zoeas (fifth stage) in the seed production. Seven seed production trials were carried out using 100 kL concrete tanks. The larvae were reared on rotifers and after the third or fourth zoeal stage with Artemia nauplii. Minced mysid was also given from the megalopal stage. The seven trials were based on the addition of different concentrations of the marine phytoplankton Nannochloropsis or of the freshwater Chlorella to the larval rearing water. The survival rate, morphological features of the fifth stage zoeas, and frequency of abnormal molting during the metamorphosis to megalops were examined. The mass mortality occurred during the metamorphosis to megalops in tanks containing high concentrations of Nannochloropsis. The fifth stage zoeas in these tanks were equipped with some advanced morphological features similar to those of megalops, such as, long endopods of the second antennae, large chelipeds and pleopods with plumose setae. The frequency of abnormal molting tended to increase depending on the degree of megalopal features in the fifth zoeal stage. We propose that zoeal morphogenesis is accelerated by the nutritional conditions of zoeas due to the supplementary effect of Nannochloropsis, which contains eicosapentaenoic acid; an essential fatty acid for larval mud crab.
Two experiments were conducted to determine a suitable feeding schedule and the optimal density of Artemia nauplii on the survival and development of mud crab Scylla serrata larvae. The first experiment consisted of 10 treatments, where rotifers were shifted to Artemia nauplii at the zoea (Z) 1, 2, 3, 4 and 5 stages. Five other treatments were similar to these first five; however, rotifers were continuously added together with Artemia nauplii. The second experiment consisted of five treatments that were carried out to determine the optimal Artemia nauplii density. Four treatments fed different Artemia densities (0.5, 1, 1.5, 4 individuals (ind.)/mL) and in the fifth treatment the density of Artemia nauplii was increased with the developing zoeal stage. The survival rate until the Z5 stage was higher when Artemia were supplied from the Z3 stage (P < 0.05). Mortality caused by cannibalism was observed either when Artemia feeding was delayed or when fed at a low density (0.5 ind./mL). In contrast, feeding Artemia from the early zoeal stage or at a high prey density (4 ind./mL) accelerated metamorphosis and caused the acceleration of morphological characteristics, such as a greater chela length, carapace length and setae bearing pleopods at the Z5 stage. The chela length at the Z5 stage decreased proportionally with the delay of Artemia feeding or a decreasing prey density. The chela to carapace length ratio (ChL/CL ratio,%) could be used as an indicator to predict the success of survival to megalops. A ChL/CL ratio over 45% produced a high percentage of megalopal molting failure. Therefore, to avoid cannibalism or excessive feeding in the larval mud crab, Artemia should be given from the Z3 stage at an optimal level of 1.5 ind./mL or increasing density according to the zoeal stage.
The present study was conducted to investigate the effect of eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA) on the survival and the occurrence of molting failure to megalops of mud crab Scylla serrata larvae fed enriched Artemia. Survival rate, intermolt period, carapace width at the first crab stage, ratio of chela to carapace length at the fifth zoeal stage and the occurrence of molting failure to megalops were observed. Mud crab larvae were reared in 1-L plastic beakers and fed with Artemia enriched at five different levels of EPA (0.31% to 1.36% EPA; referred to as E25, E50, E75 and E100) or four different levels of DHA (0.75-0.95% EPA and 0.49-1.38% DHA; referred to as D25, D50, D75 and D100). As a negative control, larvae were fed Artemia enriched with oleic acid (OA). Mud crab larvae fed Artemia containing low (0.41-0.45% EPA and trace DHA) or high (1.36% and 0.95% EPA and 0.16% and 1.38% DHA) amounts of EPA and DHA showed a significantly lower survival rate and prolonged intermolt period (P < 0.05). Moreover, a high frequency of molting failure to the megalops stage (34 and 33%) occurs coincident with a high chela to carapace length ratio (43 and 44%) in mud crab larvae fed high amounts of EPA and DHA (E100 and D100), suggesting that both of these treatments contain EPA and DHA in excess. These results indicate that during Artemia feeding, EPA and DHA content should be adjusted to 0.71-0.87% and 0.49-0.72% for maintaining a high survival, accelerating the intermolt period, and producing larger carapace width in the first crab stage.
The present study evaluates the use of rubber seed meal (RSM) and its defatted product on the growth and feeding performance of common carp Cyprinus carpio L. Digestibility test using chromium oxide as a tracer showed that defatted RSM (DRSM) resulted in significantly higher total feed, protein, Ca and P digestibility than those of unprocessed RSM (URSM). Growth test was performed with a control and three experimental diets which were 50% DRSM (50% of protein originated from DRSM), 75% DRSM (75% of protein originated from DRSM) and 50% URSM (50% protein originated from URSM). The use of diet containing URSM to replace 50% protein source resulted in the lowest growth and feeding performance which might correlate to the high cyanide content (1.16%) in the diet. Furthermore, providing the fish with this particular experimental diet also caused decline in fish haematological parameters and increased abnormalities in the fish intestine and kidney. Overall results suggested that the use of defatted RSM to replace 50% of other protein sources resulted in a comparable growth and feeding performance of common carp juvenile without any adverse effect.
The experimental diets containing five levels of creatine supplementation, namely control (N = 0 g/kg creatine), B1 (1.00 g/kg glycine), B2 (0.40 g/kg creatine), B3 (0.80 g/kg creatine) and B4 (1.20 g/kg creatine) were tested to red tilapia up to apparent satiation 3 times a day for 56 days. After the feeding trial, fish were stressed by air exposure for challenge test against stress. The results described that creatine supplementation improved final body weight, feed conversion ratio (FCR) and protein retention. Creatine supplementation decreased blood glucose, cholesterol and triglyceride levels (p < .05), indicating more effective usage of non‐protein energy. Furthermore, creatine supplementation also increased plasma insulin levels and upregulated IGF‐1 and GLUT4 gene expressions in the liver significantly; it also improved robustness against stress, which was shown by higher superoxide dismutase, higher postchallenge survival and plasma cortisol, malondialdehyde and lower glucose levels. In conclusion, creatine supplementation at a dose of 0.289–0.389 g/kg diet escalated fish growth and improved robustness against stress via improving the SOD activity in red tilapia.
New cultured ornamental fish namely Lake Kurumoi rainbowfish Melanotaenia parva (Allen) run into reduced of colour performances when reared in the aquaria, consequently, fish feed must be added with carotenoids as a pigment source. The aim of this study was to evaluate the digestibility, growth and pigmentation of astaxanthin, canthaxanthin and lutein in diet. Apparent digestibility coefficients (ADC) of dry matter, lipid, protein, carotenoids, growth and pigmentation were studied in twenty fish after 14 and 56 days of observation. The single‐dose supplementation of 100 mg/kg of astaxanthin, canthaxanthin, or lutein diets on fish was fed by apparent satiation. The basal diet without carotenoids was used as control. The result showed that the ADC of carotenoids of test diets was higher compared to control. Fish fed astaxanthin diet had higher survival rate (96.67 ± 2.89%), colour measurements of lightness (57.60 ± 7.46%), a*‐values (4.66 ± 1.20), total carotenoids content in skin (33.75 ± 5.02 mg/kg) and muscle (2.16 ± 0.74 mg/kg). Astaxanthin also increased the growth after 14 days (2.00% ± 0.19%/days) but there was no significantly different at the end of experiment. The yellowish‐orange colour performance was more rapidly achieved by fish fed astaxanthin diet after 28 days experimentation. These values suggested that dietary carotenoids were required and astaxanthin diet was superior to other diets for skin pigmentation of Lake Kurumoi rainbowfish.
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