Effects of dietary black soldier fly (Hermetia illucens Linnaeus) on the disease resistance of juvenile grouper (Epinephelus coioides)

Defatted black soldier fly (Hermetia illucens) diets improved hemato-immunological responses, biochemical parameters, and antioxidant activities in Streptococcus iniae-infected Nile tilapia (Oreochromis niloticus)

BACKGROUND

Challenges of limited supply and increasing prices of fishmeal have driven the aquaculture nutritionists to seek alternative sustainable protein rich ingredients to keep manufacturing aquafeeds in a maintainable and cost-effective way. Black soldier fly, Hermetia illucenslarvae meal represent great potential as a sustainable alternative to fishmeal in aquafeeds.

METHODS

Three replacement diets for fishmeal were prepared at different levels of defatted black soldier fly (Hermetia illucens) meal (DBSFM): Diet 1 (0 g DBSFM /kg diet, control), 33% (DBSFM-33%, 66 g DBSFM /kg diet), and 100% (DBSFM-100%, 200 g DBSFM /kg diet) to investigate their effects on biochemical parameters, immuno-hematological responses, antioxidant activities, and inflammatory gene expression in Nile tilapia, Oreochromis niloticus, a total of 270 (40.0 ± 0.50 g) before and after challenge with Streptococcus iniae (S. iniae). The feeding trial lasted six weeks (pre-challenge) and two weeks (post-challenge).

RESULTS

The results showed a significant improvement in white blood cell count (P < 0.01), lymphocyte count (P < 0.01), serum lysozyme activity (P < 0.001), and phagocytic activity (P < 0.001), mostly in the DBSFM-100% group following the pre-challenge phase compared to the control group. Post-challenge phase exhibited significant increases in blood indices in the DBSFM-treated groups compared to the control group. Following pre- and post-challenge periods, both DBSFM-supplemented groups experienced significant increases (P < 0.01, P < 0.001), in serum total protein levels. Albumin and globulin levels also experienced similar increases (P < 0.05, P < 0.01), but only post-challenge. Total antioxidant capacity exhibited a significant increase in both DBSFM-supplemented groups following the post-challenge, as did superoxide dismutase, catalase, and glutathione peroxidase in the liver and spleen. Conversely, levels of glucose, cortisol, and malondialdehyde followed the opposite trend. DBSFM-100% inclusion revealed significant (P < 0.05) up-regulation of interleukin 1β (IL-1β) in the pre-challenge phase compared to control, but no significance (P > 0.05) was seen for other genes. Anti-inflammatory-related genes transforming growth factor-β and interleukin-10 mRNA expression levels were up-regulated in DBSFM-supplemented groups compared to the control post-challenge, but the opposite was seen for IL-1β and tumor necrosis factor- α.

CONCLUSION

These findings suggest that Nile tilapia challenged with S. iniae may experience significant enhancements in hemato-immunological parameters, antioxidant capability, and anti-inflammatory gene expression when fish meal is replaced with DBSFM up to 100%.

Effect of Fish Meal Substitution with Black Soldier Fly (Hermetia illucens) on Growth Performance, Feed Stability, Blood Biochemistry, and Liver and Gut Morphology of Siamese Fighting Fish (Betta splendens)

Insects such as black soldier fly larvae (BSFL) are gaining interest among researchers and the aquafeed industry due to the fluctuating price and supply of fish meal (FM). This study evaluated the growth performance, feed stability, blood biochemistry, and liver and gut morphology of Betta splendens using BSFL as an alternative to FM. Five formulated diets were prepared: 0% BSFL, 6.5% BSFL, 13% BSFL, 19.5% BSFL, and 24.5% BSFL. The expansion rate, pellet durability index, floatability, bulk density, and water stability of the prepared feed have been assessed. Except for the diameter of the feed, all the parameters studied differed significantly (p < 0.05) across the experimental diets. After 60 days, the fish fed with 13% BSFL had the highest final length, final weight, net weight gain, specific growth rate, weight gain, and gastrointestinal weight, with mean and standard deviation values of 3.97 ± 0.43 cm, 3.95 ± 0.1 g, 2.78 ± 0.1 g, 4.63 ± 0.17, 4.65 ± 0.13, 237.26 ± 7.9%, and 0.04 ± 0.01 mg, respectively. Similar blood haematology and biochemical properties, including corpuscular volume, lymphocytes, white blood cells, red blood cells, haematocrit, albumin, and alkaline phosphatase, were the highest (p < 0.05) in the 13% BSFL diet group compared to the other treatment groups. In addition, BSFL had a significant impact (p < 0.05) on villus length, width, and crypt depth for the anterior and posterior guts of B. splendens. The 13% BSFL diet group had an intact epithelial barrier in the goblet cell arrangement and a well-organized villus structure and tunica muscularis, compared to the other treatment groups. Furthermore, the liver cell was altered with different BSFL inclusions; the 13% FM group demonstrated better nuclei and cytoplasm structure than the other treatment groups. In conclusion, replacing 13% FM with BSFL could improve the growth performance, blood parameters, and liver and intestine morphology of B. splendens, thus providing a promising alternative diet for ornamental freshwater fish.

Immune response of large yellow croaker Larimichthys crocea towards a recombinant vaccine candidate targeting the parasitic ciliate Cryptocaryon irritans

Cryptocaryon irritans, a parasitic ciliate, pose a major threat to marine teleost fish aquaculture. So far, no effective and safe control method is available. In this study, the protective efficacy of a recombinant truncated surface antigen of C. irritans (rCiSA32.6t) for large yellow croaker (Larimichthys crocea) against the parasite challenge with a sub-lethal dose of the infective theronts was evaluated by comparing the relative percent survivals (RPS), the specific antibody titers in sera, and the expression levels of the immune-related genes among the negative or adjuvant control fish, fish intraperitoneally immunized with rCiSA32.6t. The results showed that a RPS of 50.1% in rCiSA32.6t-immunized fish was achieved in comparison to negative control fish against C. irritans. A significant increase was noted in the antigen-specific immunoglobulin M (IgM) and immunoglobulin T (IgT) antibody levels in the sera of the rCiSA32.6t-vaccinated fish. Compared to the negative control fish, quantitative real-time PCR analysis indicated that the interleukin-1beta, IgT, and IgM heavy chain mRNA level in the fish head kidney, spleen, gill, and skin tissue were upregulated post-rCiSA32.6t immunization. This study indicates that the rCiSA32.6t can provide a high level of immune protection against C. irritans infection in grouper and is therefore pursued as a candidate C. irritans vaccine.

Host responses against the fish parasitizing ciliate Cryptocaryon irritans

The parasitic ciliate Cryptocaryon irritans, which infects almost all marine fish species occurring in both tropical and subtropical regions throughout the world. The disease, cryptocaryonosis, accounts for significant economic losses to the aquaculture industry. This review attempts to provide a comprehensive overview of the biology of the parasite, host-parasite interactions and both specific and non-specific host defense mechanisms are responsible for the protection of fish against challenge infections with this ciliate. Also, this article reflects the current interest in this subject area and the quest to develop an available vaccine against the disease. Due to the high frequency of clinical fish cryptocaryonosis, the study of fish immune responses to C. irritans provides an optimal experimental model for understanding immunity against extracellular protozoa.