Physiological Response of Grower African Catfish to Dietary Black Soldier Fly and Mealworm Meal.

A six-week experiment was carried out to test the effects of total (100%) and partial (50%) replacement of fish meal in the diet of African catfish growers with black soldier fly (B) meal, yellow mealworm (M) meal, and a 1:1 combination of both (BM) on the production and health of fish. A total of 420 fish with an average initial body weight of 200 ± 0.5 g were randomly distributed in triplicate to seven diet groups (C, B50, B100, M50, M100, BM50, and BM100, respectively). The growth performance and feed utilization of fish fed with partial or total replacement levels of FM with B were not significantly affected (p > 0.05) during the 6 weeks of feeding. In contrast, significant differences were observed between the groups fed with a diet where FM was totally replaced with M meal and the control in terms of final body weight, specific growth rate, feed conversion ratio, protein efficiency ratio, and protein productive value. Among the blood plasma biochemistry parameters, total cholesterol exhibited a significant difference (p = 0.007) between the M treatments and the control diet. The fatty acid profile of the liver was changed with respect to the long-chain polyunsaturated fatty acid content in all experimental groups. Parallel with this, the upregulation of elovl5 and fas genes in liver was found in all experimental groups compared to the control. Overall, this study shows that fish meal cannot be substituted with yellow mealworm meal in the practical diet of African catfish without compromising the growth, health and feed utilization parameters.

Production and efficacy of an Aeromonas hydrophila recombinant S-layer protein vaccine for fish.

A recombinant protein for the S-layer protein of Aeromonas hydrophila was produced and its ability to protect common carp Cyprinus carpio L. against six virulent isolates of A. hydrophila was assessed. A group of 120 carp (30-40 g) were vaccinated intra-peritoneally with 0.1 ml of adjuvanted vaccine (30 microg protein per fish). Another group of 120 carp were injected with 0.1 ml of PBS-adjuvant mixture to serve as controls. Twenty fish from each group were challenged with each one of six virulent isolates of A. hydrophila 35 days post-vaccination. The fish were maintained in 12 separate tanks before terminating the experiment at 16 days post-challenge. The relative percentage survival (RPS) for the six isolates of A. hydrophila ranged from 56 to 87%. The difference in survival rate of fish challenged with four of the isolates was statistically significant in vaccinated fish compared to control fish, when analysed using a Chi-square test. The results of the study suggest that the recombinant S-layer protein of A. hydrophila could be useful as a vaccine antigen to protect fish against different isolates of this pathogenic bacterium.

Immune responses of resistant and sensitive common carp families following experimental challenge with Aeromonas hydrophila.

Parameters of non-specific immune response and level of specific and natural antibodies were investigated after an experimental challenge with Aeromonas hydrophila in genetically different common carp (Cyprinus carpio) families. Ten resistant and ten sensitive families were used for the experiment, which had been selected out of 96 families, based on the results of a preliminary challenge test. Blood samples were collected 12 h, one week and 21 days following the challenge. Phagocytic and respiratory burst activities of phagocytic cells, lysozyme activity of the blood plasma were determined. Level of specific antibodies against A. hydrophila and level of natural antibodies were measured in the samples taken on the 28th day. Non-infected fish from resistant and sensitive families were used as controls. Significant differences of phagocytic and lysozyme activities were measured between the challenged resistant and sensitive families. The level of specific antibodies between the same families was also found to be significantly different. There were no significant differences of the studied parameters between the control groups. Based on our results, phagocytic activity of leukocytes, plasma lysozyme activity and specific antibody titre were found to be higher in the resistant families than in the sensitive ones following infection with A. hydrophila.

Differences in the antibody response and survival of genetically different varieties of common carp (Cyprinus carpio L.) vaccinated with a commercial Aeromonas salmonicida/A. hydrophila vaccine and challenged with A. hydrophila.

Males of two strains of carp, wild Duna (D), and inbred Szarvas 22 (22), were selected for high and low stress response. Two purebreds of D and 22, from randomly chosen parents and four crosses, 22 x 22-L (low stress response), 22 x 22-H (high stress response), 22 x D-L (low stress response) and 22 x D-H (high stress response) from selected stress response parents were produced and vaccinated with a commercial Aeromonas salmonicida/Aeromonas hydrophila vaccine and their circulating antibody response evaluated 1, 3, 5, and 7 weeks post-vaccination by ELISA. Significantly higher titres of circulatory antibodies against A. hydrophila were found in the families 22 and cross 22 x 22-L compared to other groups. The development of circulatory antibodies against A. hydrophila in all crosses having at least one D parent was low and remained low throughout the experiment. The level of circulatory antibodies against atypical A. salmonicida in the inbred strain increased following a booster vaccination with the highest values measured in inbred strain 22 and cross 22 x 22 L. The different varieties of carp had different levels of survival against experimental challenge with A. hydrophila. The greatest survival was obtained in strain 22 and cross 22 x 22-L, while ~90% of D wild carp and cross 22 x D (independent of their stress response) died. Survival results correlated well with the antibody response of the different groups: 22 and 22 x 22-L had the highest antibody titres against A. hydrophila and the greatest level of survival.

Protein expression by Aeromonas hydrophila during growth in vitro and in vivo.

Expression of Aeromonas hydrophila cellular and extracellular products (ECPs) was examined following culture of the bacterium in vitro, in Tryptic Soy Broth (TSB), and in vivo, in dialysis tubing placed within the peritoneal cavity of common carp (Cyprinus carpio L.). Whole cell (WC), outer membrane proteins (OMPs) and ECP components of the bacteria were analysed by 1 dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (1D SDS-PAGE). Additionally, 2D SDS-PAGE was used to analyse WC preparations. The aim of the study was to identify unique and common proteins up-regulated in vivo. Unique bands were seen in the 1D gels at 58 and 55 kDa for WC and OMP preparations, respectively, for all the four virulent and two avirulent isolates cultured in vivo. Bands of increased intensity were also observed at 70, 55, 50 and 25 kDa with WC preparations for all virulent isolates cultured in vivo. Analysis of WC by 2D SDS-PAGE revealed that bacteria cultured in vivo expressed a number of unique spots, mostly between 30 and 80 kDa with pI values ranging from 5.0 to 6.0. The unique proteins identified in vivo may be involved in the virulence of the bacterium and their potential as vaccine candidates is currently being investigated.