Effects of dietary peppermint (Mentha piperita) essential oil on survival, growth, cannibalism and hepatopancreatic histopathology of Portunus pelagicus juveniles

A two-part experiment was performed to determine whether dietary peppermint oil could improve the growth and/or decrease aggression among blue swimmer crab, Portunus pelagicus early juveniles. A total of five isonitrogenous diets were made that contained increasing peppermint oil levels of 0.00, 0.05, 0.10, 0.50 or 1.00%. These diets were fed to 45 replicate crabs in each treatment (total of 225 crabs) for 12 days, the final sizes and weights were measured, and then placed in 3 replicate containers (30 in total/treatment) to allow the opportunity for cannibalism over 10 days. After 10 days, the remaining crabs were examined for any histopathological changes in gills or hepatopancreas. Results showed dietary peppermint oil, at the tested levels, had no effect on the growth or cannibalism, in either experiments (p > 0.05). However, there were substantial changes in the hepatopancreatic histopathology that included thinner tubules and significantly less B- and R-cells from 0.10% dietary peppermint oil and above. The unaffected growth or cannibalism indicate that the levels of dietary peppermint oil used were insufficient and further investigations are required, particularly on the implications to the hepatopancreatic changes

Effects of different dietary organic acids on the survival, growth, and hepatopancreatic histopathology of the blue swimmer crab Portunus pelagicus

Organic acids are receiving increasing attention as a potential means to improve the growth as well as nutrient utilization of aquatic animals. A 20-day experiment was conducted to compare the effects of different dietary organic acid salts that included sodium acetate, sodium citrate, sodium butyrate, or sodium propionate at 2%, on the survival, growth, and hepatopancreatic histopathology of blue swimmer crab Portunus pelagicus early juveniles. All diets were isonitrogenous and were provided to apparent satiation twice daily. Crabs were kept individually within plastic containers, and there were 45 replicate crabs for each treatment. Results showed that, by the third molt, all the tested dietary organic acids significantly (P < 0.05) accelerated the molting (7.16–8.65 days) of the crabs compared with those in the control treatment (10.03 days). The specific growth rate (SGR) for width and length as well as the final dry weights were significantly higher (P < 0.05) in all the organic acid treatments, while SGR for weight was significantly higher (P < 0.05) in the sodium acetate and sodium propionate treatments, compared with the control. Hepatopancreatic histopathology revealed no structural differences in all treatments or staining intensity for glycogen. To our knowledge, this is the first reported study showing improvements to the survival and growth of crabs fed with inclusions of dietary organic acids

Population parameters of two common mantis shrimps species of Pantai Remis coastal waters

The study is an effort to estimate the length-weight relationship, sex ratio and population parameters of two common mantis shrimps collected from the coastal waters of Pantai Remis, Perak between February 2012 and October 2012 using trawl nets. The two common mantis shrimps collected are Harpiosquilla harpax and Miyakea nepa. A total length and weight of 804 specimens of H. harpax and 695 specimens of M. nepa were measured and the sex ratio for H. harpax is 1:0.83 (males: females) while for M. nepa, the sex ratio is 1:1.46 (males: females). Males of H. harpax were predominant than the females and females were predominant for M. nepa throughout the study period. For the length-weight relationship, both species exhibit negative allometric for males, females and combined sexes as their value is below 3. The value of b for H. harpax were 2.698 for males and 2.884 for females while for M. nepa the value of b were 2.480 for males and 2.481 for females. For combined sexes of both species, value of b was 2.852 for H. harpax and 2.412 for M. nepa. FiSAT II software package was used to estimate the growth and mortality parameters such as asymptotic length (L∞), growth coefficient (K), total mortality (Z) and natural mortality (M), exploitation rate (E) and recruitment pattern. The L∞ and K for H. harpax were 18.38 cm and 1.10 yˉˡ for males and 21.53 cm and 0.75 yˉˡ for females while for M. nepa, the L∞ and K were found to be 16.28 cm and 1.10 yˉˡ for males and 17.73 cm and 0.75 yˉˡ for females. The growth performance index (φ') for H. harpax was 2.57 for males and 2.541 for females while for M. nepa, the growth performance index (φ') was 2.465 for males and 2.372 for females. Total mortality (Z), natural mortality and fishing mortality for H. harpax was 4.084 yˉˡ for males and 3.259yˉˡ for females, 2.247 yˉˡ for males and 1.674 yˉˡ for females, 1.837 yˉˡ for males and 1.585 yˉˡ for females respectively. Total mortality (Z), natural mortality and fishing mortality for M. nepa was 3.648 yˉˡ for males and 3.248 yˉˡ for females, 2.325 yˉˡ for males and 1.767 yˉˡ for females, 1.323 yˉˡ for males and 1.481 yˉˡ for females respectively. The recruitment patterns of both species were continuous throughout the year. The exploitation rate (E) for H. harpax were 0.499 for males and 0.486 for females while for M. nepa, the rate of exploitation (E) were 0.363 for males and 0.456 for females

Assessing the feasibility of dietary soybean meal replacement for fishmeal to the swimming crab, Portunus pelagicus, juveniles

The feasibility of dietary soybean meal (SBM) replacement for fishmeal was evaluated to the swimming crab Portunus pelagicus juveniles over six consecutive molts by measuring their growth, development, hemolymph cholesterol, triglycerides, phosphate, whole-body crude protein and cholesterol as well as hepatopancreatic trypsin activity, histopathology and glycogen reserves. A total of six isonitrogenous, isolipidic and isoenergetic diets were formulated with SBM replacing fishmeal at 0 (control), 20, 40, 60, 80 or 100% of total dietary protein. Each treatment consisted of 30 replicate crabs starting from the first juvenile stage and after the crabs molted to the seventh stage, three-day post molt crabs were sampled. Results showed that crabs fed the 20% SBM diet had the best growth, which was significantly higher than the control diet (0% SBM). Growth became significantly lower in the 60% dietary SBM treatment and above, while hemolymph cholesterol, triglycerides and phosphate significantly decreased with increasing dietary SBM. The whole-body moisture, crude protein and cholesterol were unaffected by dietary SBM. Meanwhile, hepatopancreatic trypsin activity significantly decreased in the 20 to 60% SBM treatments, with a further significant decrease in the 80 and 100% SBM treatments. Hepatopancreatic damage, significantly fewer epithelial cells and glycogen reserves occurred at 60% SBM and above. Results indicate that dietary SBM can replace up to 40% of fishmeal in the diets of P. pelagicus juveniles without reducing their growth or hepatopancreatic condition