36 SEPTEMBER 2016 • WORLD AQUACULTURE • WWW.WAS.ORG Lactobacillus can contribute to a well-balanced bacterial flora in the digestive tract of culture animals, minimizing disease occurences. Although not dominant in the normal intestinal microbiota of crustaceans, some strains can colonize the gut. Artificial Lactobacillus populations can be maintained in the digestive tract of cultured animals through consistent supplementation. Feed polyunsaturated fatty acid levels, competition for nutrients, salinity and stress are factors that influence colonization of the gut by Lactobacillus. Feed is the main nutrient supply source for proliferation of certain Lactobacillus in the gut. Lactobacillus is not isolated commonly from aquaculture larvae because water temperature, incubation period and environmental glucose levels can affect their density and share of the overall bacterial level. Detection of Lactobacillus colonies in culture water and larvae following probiotic supplementations illustrates the ability to retain these bacteria in aquaculture conditions. Use of Probiotics in Crab Culture The use of probiotics to control pathogenic bacteria in crab culture has been gaining attention and various species have been tested with promising results. Lactobacillus was isolated from the digestive tract of blue swimmer crab Portunus pelagicus and used in the larval culture water (Talpur et al. 2012). A combination of Lactobacillus species (L. plantarum, L. salivarius, and L. rhamnosus) was inoculated into the culture water once daily at 1 × 102 cfu/mL, 5 × 102 cfu/mL, and 1 × 103 cfu/mL of culture water. Lactobacillus caused significantly greater survival of larvae compared to the control. The probiotics reduced the pH levels and caused a higher digestive enzyme activity compared to the control. Enzyme (protease and amylase) activities in the treated groups were greater than in the controls, indicating the effectiveness of L. plantarum in improving digestive enzyme activity. Probiotics can provide supplemental digestive enzymes, improve larval development, and FCR, and reduce gut diseases. Throughout larval developmental, probiotic bacteria can grow in the digestive tract of larvae, while utilizing carbohydrates and synthesizing amylase, protease, and lipase. A mixture of Lactobacillus species gives additional protection during unfavorable conditions and invasion by pathogenic bacteria in P. pelagicus larvae (Talpur et al. 2012). Improved defenses of larvae when several species of probiotics were used together may be the result of each species providing a specific advantage, resulting in a wider range of beneficial effects. The greatest enzyme activity in P. pelagicus occurred with mixtures of three Lactobacillus species at 1 × 103 cfu/ ml followed by 5 × 102 cfu/ml (Talpur et al. 2012). Portunus pelagicus larvae were offered live feed, suggesting the zooplankton prey had ingested probiotics from the treated culture water, improving immunity and digestion in crab larvae. Digestion in larval marine crabs was activated during the early growth phase, during which Lactobacillus secreted a wide variety of enzymes. Activities of protease and amylase were significantly greater in crab larvae in tanks receiving the mixture of Lactobacillus compared to the control (Talpur et al. 2012). It was likely that probiotics influenced digestion by enhancing beneficial bacterial populations, enzyme activity, intestinal bacterial balance, digestibility, and nutrient absorption, resulting in improved survival rates from the enhanced capability of larvae to cope with pathogens. Pathogenic Effects of Vibrios Early Scylla larvae are feeble, have an under-developed immune system and are vulnerable to pathogenic bacteria. Vibrio is one of the most important pathogens of cultured aquatic crustaceans and have been implicated as the principal disease in crustacean larviculture facilities. Vibrio parahaemolyticus affects juvenile and adult crabs. Vibrio harveyi and V. parahaemolyticus are highly pathogenic to FIGURE 5. Scylla paramamosain zoea larval stages: (A) Z1, (B) Z2, (C) Z3, (D) Z4, and (E) Z5. (A) (B) (D) (C) (E)
RkJQdWJsaXNoZXIy MjExNDY=