Effects of antimicrobial peptides on growth,morphology of foregut villi and related genes mRNA expression in the common carp (Cyprinus carpio)

A 60‐day feeding trial was conducted to examine the effects of different levels (0, 100, 200, 400 and 600 mg/kg) of antimicrobial peptides on growth, protease activity of foregut, the morphology of foregut villi and related genes mRNA expression level in the common carp (Cyprinus carpio). The results showed that the feed of antimicrobial peptides promote common carp growth, and the optimal dosage of antimicrobial peptides is 200–333 mg/kg in the common carp feed. The protease activity of 200 and 400 mg/kg groups were significantly higher than the control and other groups (p < 0.05). The foregut villus height with 100, 200 and 400 mg/kg antimicrobial peptide groups were significantly higher than control group (p < 0.05). The crypt depth of 200 and 400 mg/kg antimicrobial peptide groups were significantly lower than control group (p < 0.05). The ratio of villus height and crypt depth of 100, 200 and 400 mg/kg antimicrobial peptide groups were significantly higher than control group (p < 0.05). The ratio with 600 mg/kg group was significantly lower than the control group (p < 0.05). The IGF‐I gene expression level of 200 mg/kg and 400 mg/kg groups were significantly higher than the control group and 600 mg/kg group (p < 0.05). The IL‐1β gene expression level of 100 mg/kg and 200 mg/kg groups were significantly higher than the control group (p < 0.05). These results indicated up‐regulation of growth and immune related genes in antimicrobial peptides fed common carp. Correlation analysis showed that IGF‐I mRNA and IL‐1β mRNA were positively correlated with SGR. IL‐1β mRNA and FCR were significantly negative correlated. It indicated that growth and immune gene common regulated the growth of the carp under antimicrobial peptides intervention. In conclusion, antimicrobial peptides can improve growth and related genes mRNA expression in the common carp. Further studies using molecular biological technique or immunologic methods are required to conclude that antimicrobial peptides are beneficial in common carp.     

Early development and allometric growth in hatchery‐reared Eurasian perch,Perca fluviatilis L.

The morphological development and allometric growth patterns of Eurasian perch, Perca fluviatilis L., a highly valued commercial species, were studied under intensive rearing conditions from hatching up to 50 DPH (Days Post Hatch). Based on the external morphology, four different phases during early development of Eurasian perch were identified: pre‐flexion larva 0–20 DPH (5.70–10.16 mm TL); flexion larva 22–30 DPH (11.09–15.14 mm TL) and post‐flexion larva/juvenile 32–50 DPH (18.00–24.75 mm TL). The results indicate that growth period when final replacement of all temporary (larval) structures and most important changes in the shape of P. fluviatilis occurred (between 13.95 and 24.06 mm TL, during flexion and post‐flexion phase) can be considered as a transitional period between the larva and juvenile. All body segments, except trunk length and tail length showed fast growth (positive allometry) throughout the entire studied period or up to the respective inflexion point with a common tendency to isometry. In addition, the specific behaviours (e.g. pelagic way of life) of Eurasian perch larvae resulted in some characteristic allometric growth patterns in the posterior region, different from the majority of other teleosts. The results are discussed with respect to the ontogeny of the functional morphology under both ecological and aquaculture considerations.     

Fish photobacteriosis—The importance of rapid and accurate identification of Photobacterium damselae subsp. piscicida

MALDI‐TOF MS was tested for the identification of Photobacterium damselae subsp. piscicida on isolates grown on two media, cultured at three incubation times and applied on the target plate by the direct sample spotting (DS), by the on‐target extraction (OTE) and by the full extraction (FE) method, in triplicates. The identification of samples grown on blood agar (BA) outperformed identification on tryptic soya agar (TSA) by 0.64% for DS and OTE. The OTE gave the highest scores in both culture media, all incubation times and replicates. Reliable 24‐hr species identification was 61.54%, 84.61% and 53.85% for samples grown on TSA and identified by DS, OTE and FE, respectively. For isolates grown on BA, they were 76.92%, 96.15% and 30.77%, respectively. When identified by OTE, the 48‐hr identification was 93.58%, but for 72 hr declined to 71.79%. The reliable identification with the highest score from the first measurement was 100% only for OTE from BA (24 hr), whereas OTE from TSA gave 84.61% (24 hr), 76.92% (48 hr) and 84.61% (72 hr). The reliable MALDI‐TOF MS identification of Ph. damselae subsp. piscicida is incubation time, media, target plate preparation and replicate‐dependent.     

Evidence for the facultative intracellular behaviour of the fish pathogen Vibrio ordalii

Vibrio ordalii is an extracellular, Gram‐negative bacterium that produces vibriosis in salmonids. While pathogenesis is not fully understood, this bacterium has numerous likely genes for adhesion, colonization, invasion factors and, as recently suggested, intracellular behaviour. Therefore, this study aimed to clarify possible intracellular behaviour for V. ordalii Vo‐LM‐18 and ATCC 33509^T in the fish‐cell lines SHK‐1 and CHSE‐214. Confocal microscopy revealed Vo‐LM‐18 and ATCC 33509^T inside cytoplasm in both fish‐cell lines at 4 hr post‐inoculation (hpi). At 8 and 16 hpi, the proportion of fish cells invaded by both strains increased. Moreover, intracellular V. ordalii were observed after 8 hpi inside mouse embryonic fibroblasts (MEF), demonstrating that entry was not due to a cellular phagocytosis process. Flow cytometry confirmed immunocytochemistry results, with both V. ordalii evidencing statistically significant differences in the number of infected cells between 8 and 16 hpi. Interestingly, V. ordalii infection did not significantly damage fish cells, as determined by LDH liberation. Viable counts at 8 hpi detected, on average for both lines, 176 ± 47 CFU/ml of culturable intracellular Vo‐LM‐18 and ATCC 33509^T cells. These in vitro findings support the facultative intracellular behaviour of V. ordalii and may be of importance for understanding pathogenicity and survival in aquatic environments.     

Dietary protein requirement of juvenile marbled spinefoot rabbitfish Siganus rivulatus

Rabbitfish are an Indo‐Pacific herbivorous marine fish that have good market demand and are suitable for aquaculture. The present work was performed to determine dietary protein inclusion necessary for optimal growth of juvenile rabbitfish Siganus rivulatus. Six diets with increasing levels of protein (10, 20, 30, 40, 50 and 60 g crude protein 100 g^?1 feed) and similar levels of gross energy (20 MJ kg^?1) were prepared and offered to S. rivulatus juveniles maintained in triplicate cages placed in two large water tanks for 49 days. Growth progressively improved with dietary protein for fish offered diets from 10% to 40% protein inclusion. Diets with greater protein levels did not improve fish growth beyond that observed in the 40% group. Daily feed intake, apparent protein utilization and feed conversion ratio decreased as dietary protein increased. Protein efficiency (PE) was greatest (1.47) in fish offered the 10% protein diet and least in fish offered the 60% protein diet (0.80). No differences in PE were observed among all other treatments (20–50%). Results of the present work suggest that minimum dietary requirement for suitable growth of S. rivulatus juveniles is 40% protein when digestible energy of the diet is 16–18 MJ kg^?1.     

Effects of dietary carbohydrate/lipid ratios on growth performance,body composition and glucose metabolism of fingerling blunt snout bream Megalobrama amblycephala

This study aimed to investigate the optimum dietary carbohydrate/lipid (CHO/L) ratio for fingerling blunt snout bream Megalobrama amblycephala (average initial weight: 6.61 ± 0.03 g). Six isonitrogenous and isoenergetic diets were formulated to contain various CHO/L ratios ranging from 1.62 to 24.20. Each diet was tested in four replicates for 10 weeks. Specific growth rate (SGR), feed conversion ratio and nitrogen and energy retention all improved significantly (P < 0.05) as dietary CHO/L ratios decreased from 24.20 to 5.64 but showed little difference (P > 0.05) as dietary CHO/L ratios ranged from 2.45 to 5.64. Hepatosomatic index increased significantly (P < 0.05) as dietary CHO/L ratios increased, whereas intraperitoneal fat ratio showed an opposite trend (P < 0.05). Opposite to moisture content, lipid content of whole body and carcass all increased significantly (P < 0.05) as dietary CHO/L ratios decreased. Liver lipid content showed little difference (P > 0.05) among all the treatments, while liver glycogen content increased significantly (P < 0.05) with increasing CHO/L ratios. High dietary carbohydrate enhanced the activities of liver hexokinase, pyruvate kinase and glucose‐6‐phosphate dehydrogenase but did not induce hyperglycaemia. Based on the second‐order polynomial regression analysis of SGR, the optimal dietary carbohydrate and lipid contents for fingerling blunt snout bream were 291.7 and 81.4 g kg⁻¹, respectively, with a corresponding dietary CHO/L ratio of 3.58.     

Parentage assignment in Haliotis midae L.: a precursor to future genetic enhancement programmes for South African abalone

The establishment and evaluation of family lines using pedigree information provides an advanced understanding of the variability that exists for complex, economically valuable traits and is a necessary step in the execution of an effective breeding programme. The aim of this study was to assign parentage to mass‐spawned Haliotis midae juveniles using species‐specific microsatellite markers. Screening of wild abalone individuals revealed that the nine loci selected complied with the minimum requirements for parentage analyses: a null allele frequency <5% as well as a high number and frequency of alleles per locus. A total of 598 individuals were genotyped (198 breeding individuals and 400 F1 progeny) from two farms, with parentage results yielding 91% and 90% successful assignment for Farms A and B respectively. This study, therefore, provided the necessary pedigree information required for controlled breeding of individual adult abalone and indicated the usefulness of the panel of microsatellite markers selected for parentage assignment.