Hydrodynamic performance of a semi-submersible offshore fish farm with a single point mooring system in pure waves and current

A physical model of a semi-submersible offshore fish farm with a scale of 1:30 has been tested in a wave-current tank. The mooring force of the fish farm in waves was measured and compared for different single-point mooring arrangements, and henceforth, a safe and reliable mooring form is chosen as the mooring system for the fish farm. On this basis, the tested results for the mooring force, heave, pitch and roll of the fish farm in waves and current are presented, in which the effect of drought was discussed. The performance of blocking water flow for the fish farm in pure current was also evaluated. It has been found that increasing the anchor chain length and adding a sinker suspending from the chain could reduce the mooring force significantly despite the fluctuations in the mooring force. During the experiments, the tested value for the heave and pitch as well as the roll has been small, which indicates that the fish farm has a good stability. The mooring force has become larger, while the heave became smaller as the drought increased. Furthermore, the current velocity inside the fish farm is significantly lower than that of its outside. According to the field test results obtained in the fish farm, the farm exhibited good adaptability and it formed a suitable environment for growing cultured fish.     

Design evaluation of a fish cage mooring system with different bridle line connections using model experiments and simulations

Because fish cage systems are strongly influenced by various marine environmental conditions such as currents and waves, structural safety design is of crucial importance during their installation. It is particularly important to design a technical solution for a mooring system. In this study, we designed four types of fish cage systems with different bridle connection arrangements (two single-rope and two multiple-rope connection methods) to evaluate the structural safety of fish cage systems based on the bridle connection arrangement and to propose an efficient design direction. The level of the structural safety of the fish cage system in terms of the resistance force, shape, and inside volume reduction ratio was found to vary according to the position of the frame lines connected to the bridle lines, the number of bridle lines, and the angle between the frame line and the direction of currents and waves. Improved structural safety was observed when the bridle lines were connected to the midpoints of the frame lines compared to those connected to the vertices, and the multiple-rope connection method was found to provide higher structural safety than the single-rope connection method. Increased fish cage system structural safety was also confirmed when the frame line orientation was 90° to the direction of currents and waves compared to that at 45°. From these findings, it can be concluded that the structural safety of a fish cage system can be improved by using multiple bridle lines to disperse the tension of the mooring lines connected to the frame lines and by installing the fish cage with the frame lines aligned at an angle that minimizes the projected area exposed to currents and waves. Moreover, the simulation technique presented in this study is expected to contribute to the efficient evaluation of the structural safety of various fish cage mooring systems designed using multiple-rope connection methods, accounting for the number and position of bridle lines connected on a frame line.     

Loading of nutrient from a land-based fish farm(Orbetello, Italy) at different times

. A marine fish farm (production ~ 100 tonnes per year) located in the Orbetello lagoon area (Tuscany, Italy) was selected to study the waste water quality discharged. The aims of study were: a) quantify the nitrogen and phosphorus discharged from the fish farm at the beginning and the end of feeding time; b) verify nutrient trend during a daily cycle, and difference of release between nitrogen and phosphorus by reared biomass. From June 1999 to May 2000, water temperature, pH, salinity, dissolved oxygen and redox were hourly recorded in output wastewater station (E). Two water sampling strategies were adopted: monthly and daily. Monthly, in E, two field water samples at 8:00 a.m. (E8), at the beginning of feeding, and at 4:00 p.m. (E16), at the end of feeding, were collected. The dissolved and particulate nitrogen and phosphorus were analysed. With respect to total dissolved nitrogen (TDN), the total ammonia (NH₃ + NH₄⁺) concentration constituted more than 64%. With respect to total nitrogen and phosphorus, the particulated component represented, respectively, the 16% and 29–36%. A 24 h water sampling, at 4:00, 10:00, 12:00 a.m and at 4:00, 8:00, 12:00 p.m., was carried out. The results showed that TDN was excreted shortly after feeding, with a peak 4 h after the end of feeding. Most of the total dissolved phosphorus (TDP) was excreted after many hours, with a peak 8 h after the end of feeding.     

Optimal stocking in intensive aquaculture under sinusoidal temperature, price and marketing conditions

When the environmental and/or market conditions of an intensive aquacultural operation vary with time, maximization of profit may require a time dependent fish stocking rate. A simplified stocking problem is formulated where temperature, market price and/or market demand change sinusoidally over the annual cycle. The fish biomass sustaining-capacity is limited by the water treatment equipment, and is expressed in terms of maximum feeding rate per unit volume of culture tanks.It is demonstrated that under such conditions, sinusoidal stocking rates produce good sub-optimal solutions. A critical element of the solution is the time delay (phase-shift) between the constraining (restricting) conditions (temperature and market), and the stocking cycle. Furthermore, if the solutions for two individual conditions have very different time delays, a combination of the two conflicting restrictions is likely to produce poor returns.     

Evaluation of the structural strength and failure for floating collar of a single-point mooring fish cage based on finite element method

Deep-water fish cage floating collar also referred to as float, bears a load in the form of waves, fishing nets, and moorings, in which the longitudinal wave force is the main type of loading. The long-term continuous effects caused by wave force could cause reduction in strength, or vibration failure in the floating collar. In this study, the peak responses of a single-point mooring (SPM) cage floating collar, due to either static or vibration loadings, were calculated by the finite element method (FEM) based on an elastic model. In this model, the float exhibited macro-plastic deformation when the stress of 26.1 MPa, generated under 100 kN load, was greater than the yield limit (25 MPa). With the increase in order modes from 1 to 18 (1.2–7.9 Hz), the stress increased. Moreover, the harmonic stress corresponding to 8 and 0.1 Hz was clearly higher than that for 0 Hz under 100 kN loads, due to structural resonance. The range of stress values due to the random vibration was 16.0–63.7 MPa, when the angular velocities (k) were in the range of 0.01–16 rad s^―1. Moreover, the transient response (34.4 MPa) was maximum when the angular velocity was 10 rad s^―1 (range 1–100 rad s^―1). The reliability rate of the entire body was 53.1% and 97.0% after 10⁸ loading cycles for 100 kN and 10 kN loads, respectively. Furthermore, the fatigue modes of the key components were determined from the outer triangular tops and inner hexagonal intersections. In short, static analysis, vibration analysis, and fatigue analysis of FEM could be used as reliable ways to evaluate structural strength and failure for floating system. Finally, the floating parts could be strengthened with partially double pipes or optimized by increasing the stiffness, and appropriate damping could be widely used.     

Changes in some components of the muscle lipids of three freshwater fish species under natural extreme cold and temperate conditions

Fatty acid composition, conjugated linoleic acid and cholesterol contents in the muscles of three freshwater fish species (Barbus plebejus escherichi, Capoeta capoeta capoeta and Rutilus rutilus) were determined under natural extreme temperate (July) and cold (January) conditions. The aim of the study was to determine whether there were differences in these components of the muscle lipids among these three fish species under extreme natural conditions. Samples were analyzed using gas chromatography. Palmitic, oleic, docosahexaenoic and eicosapentaenoic acids were the predominant fatty acids in all fish in both months. The percentages of polyunsaturated fatty acids, n − 3 polyunsaturated fatty acids, n − 6 polyunsaturated fatty acids and eicosapentaenoic + docosahexaenoic acids in the muscle of B. plebejus escherichi and C. capoeta capoeta were significantly higher in January (P < 0.05) than in July. The ratio of n − 6 to n − 3 polyunsaturated fatty acids was lower than 0.60 in all fish species, with C. capoeta capoeta showing the lowest ratio in January (0.36). The levels of cholesterol and conjugated linoleic acid ranged from 103.46 to 150.10 mg/100 g oil and from 16.27 to 35.45 mg/100 g oil, respectively, for all samples in both months. There were no statistical differences in cholesterol levels among the three fish species in July and January. Conjugated linoleic acid contents were significantly higher in January in B. plebejus escherichi and C. capoeta capoeta. Of the three species tested, the extreme temperate and cold conditions affected B. plebejus escherichi the most.     

不同储存条件的鱼油对斜带石斑鱼幼鱼生长性能和抗氧化指标的影响

为研究不同储存时间、温度、抗氧化剂添加量处理的鱼油对斜带石斑鱼生长性能和抗氧化指标的影响,实验鱼油采用如下条件进行氧化处理:储存温度:4℃、环境温度(ambienttemperature,AT):(31.5±3.5)℃;抗氧化剂添加量:30 mg/kg(EQ)、300 mg/kg(HEQ);储存时间:45、90和135 d。根据鱼油储存方式的不同共分为14个处理组,分别为T_(F+EQ)(正对照组,新鲜鱼油+EQ)、T_F(负对照组,新鲜鱼油未加EQ)、T_(4℃+45d+EQ)、T_(4℃+45d+HEQ)、T_(4℃+90d+EQ)、T_(4℃+90d+HEQ)、T_(4℃+135d+EQ)、T_(4℃+135d+HEQ)、T_(AT+45d+EQ)、T_(AT+45d+HEQ)、T_(AT+90d+EQ)、T_(AT+90d+HEQ)、T_(AT+135d+EQ)、T_(AT+135d+HEQ),配制等氮等脂饲料。选择健康幼鱼[初重(18±0.02)g]进行实验,养殖8周。结果显示,T_(4℃+45d+EQ)组增重率与T_(F+EQ)组相比无显著差异,但是显著高于T_(AT+135d+EQ)组。T_(4℃+45d+EQ)、T_(4℃+45d+HEQ)、T_(AT+45d+EQ)和T_(AT+45d+HEQ)组饲料系数较低,与T_(F+EQ)、T_F组比差异不显著,但显著低于T_(AT+135d+EQ)、T_(AT+135d+HEQ)组。T_(F+EQ)、T_(4℃+45d+HEQ)组细胞结构明显,细胞内脂肪粒大小正常,T_(AT+135d+EQ)和T_(AT+135d+HEQ)组鱼油氧化程度较高,肝细胞中脂肪淤积现象明显。T_(4℃+135d+EQ)、T_(AT+135d+EQ)和T_(AT+135d+HEQ)组的CAT活力显著高于T_(F+EQ)、T_F组,SOD和GSHPx均在T_(AT+135d+EQ)组达到最高且显著高于T_(F+EQ)、T_F组。T_(4℃+45d+EQ)、T_(4℃+45d+HEQ)、T_(AT+45d+EQ)和T_(AT+45d+HEQ)组肝脏中MDA含量与T_(F+EQ)、T_F组对比无明显差异,但是显著低于其余各组。研究表明,T_(4℃+45d+EQ)、T_(4℃+45d+HEQ)、T_(AT+45d+EQ)和T_(AT+45d+HEQ)组斜带石斑鱼鱼油生长性能和抗氧化指标相对良好,T_(4℃+45d+EQ)和T_(4℃+45d+HEQ)组更优于T_(AT+45d+EQ)和T_(AT+45d+HEQ)组,说明短期、添加抗氧化剂有利于鱼油的保存,4℃比环境温度保存效果更好。     

Comparative efficacy of MS-222 and benzocaine as anaesthetics under simulated transport conditions of a tropical ornamental fish Puntius filamentosus (Valenciennes)

There is a growing commercial interest in the fish, Puntius filamentosus , in the ornamental fish trade in India and elsewhere. The trade is, however, hampered by severe mortalities during transport of the fish owing to insufficient data available on the use of anaesthetics. To resolve this problem, we evaluated the efficacy of two anaesthetics, MS-222 and benzocaine, in sedating P. filamentosus in simulated transportation experiments and used stress response parameters such as cortisol and blood glucose levels to perform assessments. We observed that MS-222 at 40 mg L⁻¹ and benzocaine at 20 mg L⁻¹ were sufficient to induce sedation for 48 h. Above these concentrations, both the anaesthetics adversely affected the fish and resulted in mortalities. Both anaesthetics significantly lowered the blood cortisol and glucose levels compared with the unsedated controls. Importantly, the anaesthetics treatment significantly lowered the post-transport mortality in the fish. The results of the study show that MS-222 and benzocaine could be used as sedatives to alleviate transport-related stress in P. filamentosus to improve their post-transport survival and hence reduce economic loss.     

The effect of fresh seaweed and a formulated diet supplemented with seaweed on the growth and gonad quality of the collector sea urchin,Tripneustes gratilla,under farm conditions

This gonad enhancement study investigates the effect of different fresh and formulated feeds and feeding regimes on the growth and gonad quality of wild‐collected adult sea urchin, Tripneustes gratilla, under farm conditions for over 18 weeks. In the first 12 weeks (phase 1), urchins were fed fresh Ulva rigida (U); a 50:50 mixture of fresh U. rigida and Gracilaria gracilis (UG); fresh G. gracilis (G) and a formulated diet 20U (containing 20% U. rigida), and in the final 6 weeks (phase 2) of the study, diet was changed to a formulated feed (20U diet). By the end of phase 1, urchins fed the 20U diet produced gonads (50.72 ± 5.4 g) that were significantly heavier (p < .001) than the gonads of urchins fed the fresh seaweed diets (U, UG & G). By the end of phase 2, gonad weight of urchins in treatment groups UG‐20U and G‐20U were similar to those fed the 20U‐20U diet. Gonad colour of urchins in the G‐20U treatment became significantly lighter (ANOVA, p = .029) and poorer quality, compared with urchins in the U‐20U group. This gonad enhancement study, conducted on wild‐collected adult T. gratilla, has shown that a formulated feed (20U diet) can enhance gonad growth and produce commercially acceptable gonads. This farm‐based study supports previous findings from aquarium‐based studies by our group and indicates that short‐term sea urchin gonad enhancement can be carried out under farm conditions in South Africa.     

Predicting non‐native fish dispersal under conditions of climate change: case study in England of dispersal and establishment of pumpkinseed Lepomis gibbosus in a floodplain pond

Predictions of future climate change include shifts in patterns of precipitation, evapotranspiration and water run‐off, resulting in increased periods of drought as well as variability and intensity of rainfall events. In the United Kingdom, the non‐native North American sunfish, pumpkinseed Lepomis gibbosus (L.), is expected to benefit from these changes. We examine how hydrological variability induced by predicted changes in climate will affect the dispersal and spread of pumpkinseed in England by: (i) determining the relationship between discharge regime and pumpkinseed propagule pressure; (ii) examining a newly‐established pumpkinseed population following a flood event in 2007; and (iii) comparing the growth and life‐history traits of this new population with fish collected from the source population to demonstrate how the pumpkinseed's life‐history plasticity contributes to its success as a coloniser. Using Bayesian modelling, we determined that the number of pumpkinseed escapees is likely to increase with increasing discharge. The newly‐established pumpkinseed population showed fast juvenile growth, early age at maturity and small size at maturity. These traits differed significantly from the source population, specifically total length (TL) means at ages 1 and 2 were significantly greater in the new population, whereas TL at age 4 was significantly greater in the source population, and a significantly higher proportion of mature females were found at smaller size classes in the newly established pumpkinseed population. This study demonstrates the potential link between hydrological variability (current and future) and the dispersal of non‐native pumpkinseed, leading to the establishment of new populations.