Elevated temperature affects growth and hemato‐biochemical parameters,inducing morphological abnormalities of erythrocytes in Nile tilapia Oreochromis niloticus

Temperature is considered as an important environmental factor, and the increasing water temperature resulting from global warming is a great concern. The present study was conducted to examine the effects of elevated water temperature on growth, hemato‐biochemical parameters in Nile tilapia, Oreochromis niloticus acclimatized to three temperatures (31°C, 34°C and 37°C) for 60 days. Additionally, erythrocytic cellular abnormalities (ECA) and erythrocytic nuclear abnormalities (ENA) tests were assayed using peripheral erythrocytes after exposure to the three temperatures. Fish were sacrificed on days 7, 15, 30 and 60 of exposure. Growth performances viz., weight gain, % weight gain and specific growth rate (SGR) showed decreasing tendency at 34°C but significantly declined at 37°C compared to 31°C. The abundance of haemoglobin (Hb) and red blood cells (RBCs) significantly decreased in response to temperature increases, while white blood cells (WBCs) displayed the opposite response. At days 7 and 15, blood glucose levels significantly increased in response to the temperature increase, while at days 30 and 60 glucose declined. Frequencies of ECA and ENA were significantly enhanced at the highest temperature throughout the experimental period. Dissolved oxygen decreased and free CO₂ increased significantly with increasing temperature throughout the study period. The present study revealed that temperatures higher than 34°C may be hazardous to O. niloticus.     

pH水平和昼夜变化对池塘养殖凡纳滨对虾成活率的影响

为评价不同pH水平和昼夜变化幅度对凡纳滨对虾成活率的影响,采用单因素实验设计,实验Ⅰ设4个pH水平:6.6(P1)、7.6(P2)、8.6(P3)和9.6(P4),以温室养殖池塘内的平均pH水平(8.2)为对照(P0);实验Ⅱ设3个pH昼夜变化幅度:7.5～8.2(PV1)、7.5～9.5(PV2)和7.5～10.0(PV3),以养殖池塘的平均pH昼夜变化幅度(7.5～8.7)为对照(PV0)。结果显示,环境pH水平可显著影响对虾成活率、血淋巴颗粒细胞数以及血淋巴中超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)、谷胱甘肽还原酶(GR)、过氧化氢酶(CAT)、酚氧化酶(PO)和诱导型一氧化氮合酶(iNOS)的活性。P4水槽内对虾成活率显著低于P0、P1、P2和P3水槽,同时其血淋巴SOD、GSH-Px、GR、CAT、PO和iNOS的活性较后者不同程度地下降。pH昼夜变化幅度可显著影响对虾成活率、血淋巴SOD、GSH-Px、GR和CAT活性,但对血淋巴谷胱甘肽含量无显著影响。PV2和PV3水槽内对虾成活率显著低于PV0和PV1水槽,同时其血淋巴SOD、GSH-Px、GR和CAT活性较后者不同程度地降低。研究表明,环境pH水平及昼夜变化幅度可显著影响凡纳滨对虾的成活率。鉴于对虾死亡率变化伴随血淋巴SOD、GSH-Px、CAT和PO活性的变化,初步认为对虾死亡与pH胁迫产生的应激有关。因此,调控pH应是对虾池塘养殖水质管理中的一项重要措施。     

Molecular characterization and interactome analysis of aerolysin (aer) gene from fish pathogen Aeromonas veronii: The pathogenicity inferred from sequence divergence and linked to histidine kinase (cheA)

Aerolysin (aer) is one of the most important and abundant virulence factors in the infection of fish by Aeromonas veronii. A comprehensive study on the molecular characterization and pathogenicity of the aer gene from 34 A. veronii isolates from diseased carp and catfish was carried out and its interactome was analysed to observe the functional correlations between aer and other proteins within the A. veronii network. The PCR‐based amplification of aer from the 34 isolates of A. veronii showed more aer‐positive isolates from catfish with a high pathogenic potential in the in vivo challenge test than the carp fish. The analysis of aer gene sequence from challenged fish revealed significant sequence divergence according to the types and geographical distribution of the fish. The networking analysis of aer from the model A. veronii B565 revealed histidine kinase (cheA) as the most functional interacting partner. The study of the interaction between aer from the experimental A. veronii and cheA demonstrated that the A chain of cheA plays a more important role than the corresponding B chain during contact, and a linker sequence of 15 residues controlled the entire interaction process. Therefore, cheA could be an excellent drug target for controlling A. veronii infection of fish.     

The use of fermented soybean meal and squid by-product blend as a substitute for fish meal in practical diets for climbing perch,Anabas testudienus (Bloch, 1792), pond culture: Growth performance and economics analysis

A feeding trial was conducted to evaluate the effects of different ratios of fish meal (FM) to a fermented blend (FB: fermented soybean meal and squid by-product blend) on growth and economic performance of climbing perch, Anabas testudineus (Bloch, 1792), in earthen ponds. Five diets were prepared where FB was substituted for 0 (D1), 25 (D2), 50 (D3), 75 (D4), or 100% FM protein (D5), while a commercial diet (D6) was used for comparison. Triplicate groups of fish (1.03 ± 0.07 g) were fed twice daily up to satiation for 70 days in earthen ponds. No significant (P > 0.05) differences were found in growth performance of fish fed D1, D2, D3, and D6 diets, while fish growth decreased significantly (P < 0.05) in D4 and D5 groups. Feed intake decreased (P < 0.05) with the increasing levels of FB with no significant difference in the feed conversion ratio, which ranged from 1.98 to 2.08. The fish survival decreased significantly in D5 alone. While considering the overall production, the total yield and economic return were found to be highest in D2 (64176.7 TK ha^?1) and lowest in D5 (14418.3 Tk. ha^?1). Based on the present experimental condition, it is concluded that FB can economically be included in aquafeed as a substitute for up to 50% of FM protein from the diets of climbing perch.     

Interactive effects of dietary astaxanthin and cholesterol on the growth,pigmentation, fatty acid analysis,immune response and stress resistance of kuruma shrimp (Marsupenaeus japonicus)

A 56‐day feeding trial was carried out to evaluate the interactive effects of chemically synthesized astaxanthin (Ax) and cholesterol (CHO) on the performances of kuruma shrimp juveniles. Six experimental diets containing 2 levels of Ax (0 and 0.6 g/kg diet) and 3 levels of CHO (0, 6 and 20 g/kg diet) were formulated in 2 × 3 factorial design. The results indicated that the interactions between dietary CHO and Ax were not significant on survival, growth performances, body proximate analysis, immune response and freshwater stress test. Significantly, better pigmentation performances and Ax contents of different parts of juveniles (whole body, muscle, carapace and head) were observed in higher Ax (Ax_0.6)‐supplemented groups. Meanwhile, interactions of dietary Ax and CHO were also found on colour reading parameters and whole‐body Ax contents. In addition, juveniles fed with the diet containing Ax at 0.6 g/kg diet in addition to CHO at 0, 6 and 20 g/kg diet showed better performances on digestive enzyme activities (protease, lipase and amylase) of hepatopancreas than 0 g Ax/kg diet supplemented with CHO at 0, 6 and 20 g/kg diet. It was concluded that dietary Ax and CHO functioned interactively.     

Dietary supplementation of garlic (Allium sativum) modulates gut microbiota and health status of tilapia (Oreochromis niloticus) against Streptococcus iniae infection

This study was conducted to characterize the causative agent of streptococcosis in tilapia (Oreochromis niloticus) and control of Streptococcus infection by means of garlic (Allium sativum) supplementation. The morphological, biochemical and polymerase chain reaction amplification confirmed 11 isolates belong to Streptococcus iniae from the infected fish eyes and tissue samples. Random screening of 12 well‐known medicinal plant parts against S. iniae revealed the garlic extract as the most effective herbal recovery against Streptococcus infection. In vivo challenge test with dietary supplementation of garlic powder significantly improved survival rates of fish against S. iniae infections, and modulate the microbial community and cytokine gene expression profiling in the intestine of the experimental tilapia. Among the two garlic supplemented treatments, 1.0 g garlic supplemented diet significantly increased (p < 0.05) the survival rates of tilapia and the gut bacterial operational transitional units abundance for Proteobacteria and Tenericutes, the phyla associated with healthy intestinal flora. The bacterial diversity index also found high with garlic supplemented diets. Significant upregulations of IL‐10 and IL‐17F gene expression in the intestinal tissue were observed with 1.0 g garlic supplemented diet where IL‐8 and IL‐1β expression levels were relatively static. The dietary supplementation of garlic, therefore, could be effective in the prevention of S. iniae infection in fish.     

Thyroid hormone‐induced swim bladder and eye maturation are transduced by IGF‐1 in zebrafish embryos

Maternally derived thyroid hormones (THs) deposited in yolk promote fish embryogenesis and survival, and understanding early regulatory mechanisms could lead to improved seedstock production. We have tested the hypothesis that some thyroid actions may be mediated by insulin‐like growth factor I (IGF‐1), another promoter of embryo development. Differentiation and performance were assessed in embryos treated with THs in the presence or absence of an IGF‐1 receptor blocking peptide. Treatment with the TH triiodothyronine (T₃) promoted IGF‐1 gene expression at days 1 and 5, and advanced swim bladder and eye development, but blocking the IGF‐1 receptor eliminated the swim bladder and eye effects. Growth and survival at 1 week of age were impaired by the IGF‐1 receptor blocking peptide alone, but concurrent treatment with T₃ partially restored these indices. Our results confirm interaction of T₃ and IGF‐1 regulatory signalling in zebrafish embryogenesis and transduction by IGF‐1 of thyroid‐driven swim bladder and eye maturation.