利用有限酶解技术提高鲶鱼食用肉粉溶解度的研究

[目的]筛选出有限酶解鲶鱼肉蛋白的最佳用酶种类和酶解工艺条件,为鲶鱼食用肉粉的加工提供理论依据。[方法]以鲶鱼为原料,经预处理、采肉、漂洗、斩拌、有限酶解、打浆和干燥等工序加工而成鲶鱼食用肉粉。其中选择4种酶（风味蛋白酶、枯草杆菌中性蛋白酶、碱性蛋白酶和木瓜蛋白酶）作为水解用酶,分别在各酶最佳酶解条件下对鲶鱼肉糜进行水解,以鲶鱼肉粉的溶解度为评价指标。[结果]用中性蛋白酶作为有限酶解的酶类加工出的鲶鱼食用肉粉溶解度可达90%以上,最佳酶解工艺条件为：酶用量0.55%,酶解时间60 min,料水比1∶3（g∶g）。[结论]用中性蛋白酶作为有限酶解的酶类,加工出的鲶鱼食用肉粉溶解度最高,风味最佳。     

杂交黄颡鱼新品种试养效果评估

为了改良天津地区养殖黄颡鱼种质,提高经济和生态效益,本研究于2019年引进杂交黄颡鱼新品种‘黄优1号’,采用性状比较的方法,系统研究了试验鱼的生长、抗病和产氮、磷情况。结果表明：杂交黄颡鱼幼鱼生长速度、增重率显著高于普通黄颡鱼(P<0.05),饵料系数低于普通黄颡鱼,但差异不明显(P>0.05);杂交黄颡鱼的主要死亡病因为体表溃烂和烂鳃,体表溃烂发病情况与普通黄颡鱼无明显差别(P>0.05),烂鳃发病情况明显重于普通黄颡鱼(P<0.05),而其他疾病发病情况明显小于普通黄颡鱼(P<0.05),试验总成活率显著高于普通黄颡鱼;实验鱼体重增加1 kg,杂交黄颡鱼实验组尾水中氨氮、亚硝酸盐、总磷的增量均显著低于普通黄颡鱼(P<0.05),总氮的增量虽然也小于普通黄颡鱼实验组,但比较结果差异不显著(P>0.05)。因此,本研究认为杂交黄颡鱼‘黄优1号’的生长、抗病和单位增重产氮、磷量等性能较普通黄颡鱼优良,适合在天津地区推广养殖。     

Evaluation of body weight and color of cultured European catfish (Silurus glanis) and African catfish (Clarias gariepinus) using image analysis

Two cultured catfish species (European catfish Silurus glanis, and African catfish Clarias gariepinus) were evaluated for their weight estimation and colors by image analysis. A total of 60 whole fish from each species were first weighed, and then their pictures taken by a digital camera in a light box. Length, weight and color of all fish were determined by image analysis and results were compared between the two fish. Fish weight ranged from 7.4 to 39.61 g and 25.71 to 93.91 g for European and African catfish, respectively. Weight (W) vs length (L) data were fitted linear (W = A + BL), power (W = A L^B) and second order polynomial equations (W = C₀ + C₁ L + C₂ L²). The R² values ranged from 0.835 to 0.974. For the W vs view area (V) relationship, the same equations were used. The R² values for these equations ranged from 0.927 to 0.972. No significant difference was found between the average color values according to the L*, a* and b* distributions for both fish species (P > .05). Image analysis can easily determine length, view area, and color of fish and help in developing W vs L, and W vs V relationships.     

Effects of fasting on IGF-I,IGF-II,and IGF-binding protein mRNA concentrations in channel catfish (Ictalurus punctatus)

The effects of fasting on insulin-like growth factor (IGF)-I, IGF-II, and IGF-binding protein (IGFBPs) mRNA in channel catfish were examined. Fed control fish (Fed) were compared to fish that had been fasted for 30 d followed by 15 d of additional feeding (Restricted). Sequence alignment and similarity to orthologous proteins in other vertebrates provided structural evidence that the 3 catfish sequences identified in the present research were IGFBP-1, -2, and -3. Prolonged fasting (30 d) reduced body weight approximately 60% (P < 0.001) and decreased IGF-I mRNA in the liver and muscle (P < 0.01). Fifteen days of re-feeding restored concentrations of hepatic and muscle IGF-I mRNA. Liver IGF-II mRNA was not affected by fasting but was increased 2.2-fold after 15 d of re-feeding (P < 0.05). Abundance of muscle IGF-II mRNA was similar between the fed control group and the restricted group throughout the experimental period. Fasting also increased liver IGFBP-1 mRNA (P < 0.05) and decreased IGFBP-3 mRNA (P < 0.01), whereas abundance of IGFBP-2 mRNA was not significantly affected. Interestingly, re-feeding for 15 d did not restore concentrations of IGFBP-1 and IGFBP-3 mRNA relative to fed control concentrations. The IGF results suggest that IGF-I and IGF-II are differently regulated by nutritional status and probably have a differential effect in promoting muscle growth during recovery from fasting. Similar to mammals, IGFBP-1 mRNA in catfish is increased during catabolism, whereas IGFBP-3 mRNA is decreased during inhibited somatic growth. The IGFBP results provide additional evidence of the conserved nature of the IGF-IGFBP-growth axis in catfish.     

Generation of reactive oxygen species by a novel anthraquinone derivative in the cyanobacterium Planktothrix perornata (Skuja)

A water-soluble anthraquinone derivative (2-[methylamino-N-(1′-methylethyl)]-9,10-anthraquinone monophosphate), previously found to be selectively toxic towards Planktothrix perornata at submicromolar concentrations, was studied to determine its toxic mode of action towards this cyanobacterium. Chlorophyll fluorescence was monitored as an indicator of photosynthetic efficiency, and measurement of reactive oxygen species (ROS) was performed using the ROS-sensitive probe 2′,7′-dichlorodihydrofluorescein diacetate. The effects of the herbicide paraquat (a ROS generator) as well as ascorbate and α-tocopherol (ROS scavengers) on ROS formation by P. perornata were studied. Also, the effects of different concentrations of ascorbate, α-tocopherol, and the herbicide diuron on reducing the toxicity of the water-soluble anthraquinone derivative towards P. perornata were determined. Our results indicate that the water-soluble anthraquinone derivative does not inhibit photosynthetic electron transport directly, but does generate ROS at levels that may cause toxicity towards P. perornata.     

The dynamics of an exploited population of a siluroid catfish (Schilbe intermidius Reupell 1832) in the Cross River, Nigeria

We studied the breeding biology, growth, mortality, recruitment pattern and yield per recruit of a freshwater siluroid catfish (Schilbe intermedius) in the Cross River, Nigeria. Monthly variation in mean gonadosomatic and mean condition indices shows that the species breeds twice in a year (March and September). We used 12 consecutive months length–frequency data together with FiSAT software to study the population dynamics of this catfish which is exploited by artisanal fishermen. Fitting the seasonalized von Bertalanffy growth function to our length–frequency data gives the following growth parameters: L_∞=27.5 cm total length, K=0.29 yr⁻¹, C=0.5, WP=0.46. Using the seasonalized length converted catch curve, we estimated the instantaneous total mortality coefficient Z as 1.85 yr⁻¹. The instantaneous natural mortality coefficient M was 0.81 yr⁻¹ while the instantaneous fishing mortality coefficient F was 1.04 yr⁻¹, giving the current exploitation rate E=0.56. From the analysis of probability of capture of each length class we estimated the length at first capture L_c to be 10.9 cm. The relative yield per recruit analysis predicted the maximum exploitation rate E_max=0.54. The current exploitation rate E is more than this predicted maximum E_max. Thus, the species is on the verge of being overexploited.     

Influence of Washing and Cold Storage on Lipid and Protein Oxidation in Catfish (Clarias lazera) Surimi

ABSTRACT

Lipid and protein oxidation in catfish (Clarias lazera) surimi during processing and storage were assessed. Catfish surimi were washed in deionized water: M0 (no washing step), M1 (one washing step), and M2 (two washing steps). Lipid, protein, water, and iron contents were determined. M0, M1, and M2 were stored for 0, 1, 4, 7, or 10 days at 4 ± 1°C; at each time point, samples were removed for analyses. Lipid oxidation was assessed by measuring malondialdehyde content. Protein oxidation was assessed by measuring protein solubility and protein sulfhydryl and carbonyl group contents. Based on the results, lipid content, L* and a* (color parameters), and fatty acid content in M1 and M2 were significantly reduced. Lipid oxidation development was faster in M1, and the ranking was as follows: M1 > M2 > M0, with M0 being significantly less oxidized than M1. Increasing the number of washes increased protein oxidation, and the ranking was follows: M2 > M1 > M0. Altogether, lipid and protein oxidation and physicochemical changes occurred simultaneously to different degrees in surimi during various processing and storage conditions.     

Farm-level costs of settling basins for treatment of effluents from levee-style catfish ponds

Compelled by pending regulatory rule changes, settling basins have been proposed as a treatment alternative for catfish pond effluents, but the associated costs to catfish farmers have not been estimated. Economic engineering techniques were used to design 160 scenarios as a basis for estimating total investment and total annual costs. For static-water, levee-style catfish pond facilities, sizing of settling basins is controlled by factors such as type of effluent to be treated, pond layout, size of the largest foodfish pond, number of drainage directions, scope of regulations governing effluents, and the availability of land. Regulations that require settling basins on catfish farms would increase total investment cost on catfish farms by $126–2990 ha⁻¹ and total annual per-ha costs by $19–367 ha⁻¹. More numerous drainage directions on farms resulted in the greatest increase in costs. While both investment and operating costs increased with larger sizes of foodfish ponds, costs per ha were relatively greater on smaller than on larger farms. For farms on which existing fish ponds would have to be converted to settling basins, over half of the cost was due to the production foregone and annual fixed costs of the pond. Requiring catfish farmers to construct settling basins would impose a disproportionately greater financial burden on smaller farms. The magnitude of the increased costs associated with settling basins was too high relative to market prices of catfish for this technology to be economically feasible.     

Evaluation of Diquat as a Potential Algicide for Controlling the Musty-Odor-Producing Cyanobacterium,Oscillatoria perornata,in Catfish Aquaculture Ponds

ABSTRACT

The synthetic herbicide diquat was applied to a catfish aquaculture pond containing a heavy bloom of the cyanobacterium Oscillatoria perornata(a major contributor to musty off-flavor in farm-raised catfish) in order to determine the effectiveness of diquat as a selective algicide to prevent musty off-flavor in cultured catfish. Levels of the musty-odor compound 2-methylisoborneol (MIB) and numbers of O. perornata were monitored. Results indicate that diquat is not useful as an algicide for controlling O. perornata in catfish aquaculture ponds, despite its usefulness in controlling other aquatic weeds.