Design and development of a portable and streamlined nutrient film technique (NFT) aquaponic system

One pilot-scale portable Nutrient Film Technique (NFT) aquaponic system has been designed, developed, and tested at ICAR-CIFA, Bhubaneswar for a period of 90 days (October to December 2018) to study the efficiency of the new design. The experimental setup has three separate units, each consisting of four major components, such as Fibreglass Reinforced Plastic (FRP) round fish culture tank (ø2.15 × 0.9 m) with operational capacity 2800 L, biofilter unit made up of Polypropylene (PP) of 100 L capacity, FRP rectangular hydroponics tank (4 × 0.9 × 0.35 m) having 2.64 m² plantation area and High-density Polyethylene (HDPE) sump (ø0.6 × 0.7 m) of 200 L capacity. Implementation of custom designed and calibrated automatic water recirculation system gives an average flow rate of 94.7 L/h for continuous flow of nutrients from fish culture tank to hydroponics tank. The designed system harnesses gravity flow in 75 % of the cycle. For performance assessment, the system was initially stocked with 54 numbers of fish fry/m³ (153.7 g/m³) of pangas (Pangasius hypophthalmus) in culture tank and 27 marigold (Tagetes erecta) plants/m² in hydroponics tank. Length and weight gain of fish were by 77.04 % and 397.2 % from initial, respectively, and marigold plant harvested 107 number of flowers/m². The Total Ammoniacal Nitrogen (TAN) reduction in biofilter was found to be 61.97 %.     

Individual variations in behavior and free cortisol responses to acute stress in tiger pufferfish Takifugu rubripes

Abstract:   The aim of the present study was for individual variation in behavior to be characterized and related to differences in physiological stress responses in juvenile tiger pufferfish (fugu) Takifugu rubripes . A set of siblings ( n  = 330) from wild parents was subjected to behavior tests, and some were classified into active and inactive groups ( n  = 42 each group). The active animals consisted of those individuals that kept active swimming during 6 min after transfer from one tank to another, and the inactive animals were those that stopped swimming within 6 min. Time-course acute stress responses, which were elicited by anesthesia and subsequent removal of a pectoral fin, were compared between the active and inactive fish. The stress indicators used were free and total plasma cortisol, and plasma glucose. Although no significant difference was observed at each sampling point between groups, the inactive fish required shorter recovery time from acute stress in all three indicators than the active fish. The percentage of free to total plasma cortisol in the pre-stress condition was significantly lower in the inactive group than in the active group. Our findings indicate that fugu has behavioral variation that is associated with stress responsiveness. The inactive fish are expected to be more tolerant of stress and suitable for aquaculture.     

Effects of tank color on the growth,stress responses,and skin color of snakeskin gourami (<Emphasis Type="Italic">Trichogaster pectoralis</Emphasis>)

The effects of tank color on the growth, stress responses, and skin color of snakeskin gourami (Trichogaster pectoralis) were investigated in this study. Fish with initial body weights of 5.03±0.00 g were reared in five experimental tank colors (white, red, green, blue, and black) for 8 weeks. Each tank color was tested in triplicate with an initial stocking density of 15 fish per tank. Fish were fed with commercial sinking pellets at 4% of the average body weight per day. Growth performance, feed utilization efficiency, stress indicators (hematocrit, blood glucose, plasma cortisol levels), and skin color parameters were investigated. The fish reared in blue tanks had a significantly higher average final body weight (9.73?±?0.14 g) and significantly lower average feed conversion ratio (3.42?±?0.12) than the fish reared in black tanks (P?<?0.05). The fish reared in black tanks exhibited higher average hematocrit (36.63?±?1.11%), blood glucose (48.33?±?1.45 mg dL^?1), and plasma cortisol (9.00?±?0.56 μg dL^?1) levels than those reared in the other tank colors. However, the blood glucose levels in only the fish reared in black tanks were significantly higher than those in the fish reared in the other tank colors. The fish skin color ranged from very pale (high skin lightness) in the white tanks to very dark (low skin lightness) in the black tanks, and 80% of the variation in skin lightness were explained by the tank lightness. The use of a blue tank resulted in normal skin color; hence, blue tanks will not affect the customer acceptance of the fish. Our study revealed that blue is the most appropriate tank color for culturing snakeskin gourami.     

Escape‐related behaviour of Atlantic cod,Gadus morhua L., in a simulated farm situation

Cultured fish escaping from farms represent an economic loss as well as a potential problem for wild fish populations. This study investigated the escape‐related behaviour of farmed Norwegian coastal and northeast Arctic cod (NEAC), Gadus morhua L. Six groups of fish were observed during three replicate trials in a large tank that was split into two equal parts by a net wall. The fish could move freely through an opening in the net during the trials. Three groups were not fed during the trials. The first escape occurred shortly after producing the net opening (11±10.5 min; mean±standard deviation). Norwegian coastal cod were more prone to escape than the NEAC. A starvation period of 9 days increased the number of fish on the escape side of the tank. Net biting and net inspection by the fish were frequently observed, irrespective of whether the fish were fed or not. The same fish were repeatedly found on the escape side of the tank, but the propensity for recurrent escape behaviour was not related to genotype, feeding status or size. The results suggest that other factors, such as individual variation in boldness or exploration behaviour, could affect the willingness to escape.     

Behavioral Interactions in Juvenile Channel Catfish,Ictalurus punctatus

Behavioral interactions among juvenile channel catfish, "Ictalurus punctatus," were observed, and fixed action patterns were described and anlyzed. Dominant fish engaged regularly in aggressive activities and never in submissive activities, whereas subordinate fish were observed in submissive activities on a regular basis and rarely in those that were aggressive. Activity levels were significantly higher in dominant fish; however, there was no difference in activity levels between pairs of equal and unequal size fish. A factor analysis indicated that there were three general categoris of behavior in juvenile channel catfish. In addition, two behaviors (which appeared to be displacement activities) were functioning in agnostic encounters. Plasma cortisol concentrations measured in sigle fish and pairs of fish in aquaria and individuals from a holding tank indicated that the least amount of stress occurred in fish that were not interacting with any other individuals. Cortisol levels, however, were lower that those associated with stress levels in fish from other studies.     

Advances in fish harvest technologies for circular tanks

Improved equipment and husbandry practices are required to effectively grade and harvest fish in large land-based culture tanks. The objective of our work was to develop and evaluate several types of relatively inexpensive, portable, and efficient fish handling equipment to reduce the labor requirement for grading and harvesting fish from large circular culture tanks. This equipment and husbandry practices also had to provide for worker safety and minimize the stress or damage to the fish. Two techniques were developed and evaluated to remove the entire population from a large and deep circular tank, i.e. (a) purse seine and (b) carbon dioxide avoidance response. Two other techniques were developed and evaluated to remove the fish from a large (150 m³) and deep (2.44 m) circular culture tank after they had been top-graded in situ using a 3-panel clam-shell grader: (c) an airlift fish pump and hand sorting/dewatering box and (d) a sidewall drain box for hand sorting/dewatering. Some of these technologies are new, while others (such as the purse seine) have been used in other applications. Our commercial-scale evaluation of these technologies provided insight into the advantages and disadvantages of each option. With use of the clam-shell grader, the majority of the fish in the culture tank were never lifted from the water during the self-sorting process, which minimized stress, perhaps enhancing final product quality. In contrast, harvesting the tank using the purse seine and hand brailing was much more labor intensive and increased the stress on the fish, as indicated by a nearly 10-fold increase in fish mortality compared to the mortality observed when the clam-shell type crowder/grader system and an airlift fish pump or sidewall drain box were used during fish harvest. The combination of the clam-shell crowder/grader with the sidewall drain harvest box was our preferred harvest method, because of its low labor requirement, relatively low fish mortality, and rapid harvest rate. We also think that the carbon dioxide avoidance harvest technique can be used effectively, with little labor input and practically zero mortality when the entire fish population must be removed from a fish culture tank, but not during a selective harvest using in situ grading. Ultimately, the more effective technologies and practices should help fish farmers overcome scale-up issues and improve land-based fish farm profitability.     

光照条件下南极磷虾的行为观察

2010—2011年随中国大型拖网加工船“安兴海”轮在南极南奥克尼群岛附近进行南极磷虾拖网作业,将作业过程中采集到的鲜活南极磷虾立刻转移至实验水箱,进行暂养并观察其行为。实验样本为45尾,体长为37~50 mm,整个实验持续时间为13 d,水面光照为220 lx,水温恒定在0 ℃。通过观察发现:(1) 南极磷虾进入实验水箱后体色迅速变为透明;(2) 在静水环境中,南极磷虾多数时间位置相对固定,集中于角落,沿箱壁进行角落间游动,较少穿过水箱中央,穿过水箱中央时有加速游动的现象;动水环境中能够顶流游动并形成集群,0.5 m/s时顶流游动,流速超过1 m/s时,集群消失;水流对南极磷虾的集群有极显著影响;(3) 南极磷虾进入水箱后第6天开始蜕壳,第6~9天均发现虾壳,实验对象平均体长增长5~8 mm。     

Prediction of water velocities in circular aquaculture tanks using an axisymmetric CFD model

Computational fluid dynamics (CFD) software was used to construct two-dimensional axisymmetric simulations of the turbulent flow inside 1.5, 5, 9.15 and 10 m tanks containing rotating water. The water rotation was induced mathematically by either placing a rotating cover on the surface of the water or locating a tangential water inlet near the top of the side wall. Central and side drains evacuated the water from the tank when using an inlet. The rotating cover produced a forced vortex in the tanks similar to the one observed in actual rearing tanks when the majority of the flow is leaving via the side drain. The predicted flow structure in tanks with an inlet can be divided into three regions: a narrow region along the side wall where the rotating water is moving down toward the floor, a thin boundary layer along the floor where the rotating water is moving radially inward, and a large region in the bulk of the tank where radial and axial velocities are small and the tangential velocity is independent of elevation but varies with radial position. Calculations were performed with the k-ε (RNG) and Reynolds stress turbulence models. Converged solutions were easier to obtain with the k-ε (RNG) model but only the Reynolds stress model could predict the strong vortex which is experimentally observed to form in the central portion of the tank as the flow leaving via the center drains is increased. The simulations predict that the thickness of the floor boundary layer is proportional to the tank diameter and that the radial velocity within the floor boundary layer is maximum at an elevation equal to about 10% of the boundary layer thickness. At any given radial position, the maximum value of the radial velocity next to the floor is between 15 and 45% of the tangential velocity in the bulk of the tank. Predicted shear stresses along bounding surfaces were used to obtain correlations for the side-wall and floor friction coefficients in terms of the Reynolds number. These correlations were in turn substituted in an overall moment balance to obtain an analytical model for predicting the maximum tangential velocity V_θw near the side wall of multi-drain rearing tanks. The predictions of the analytical model are in excellent agreement with V_θw values reported in the literature for tanks with diameters ranging from 1.5–15 m and indicate that the drag from inlet structures is non-negligible. The results demonstrate that the axisymmetric CFD model can simulate the main features of the rotating flow inside circular tanks and provide valuable boundary-layer information that is difficult to obtain experimentally.     

Effects of Lighting Spectrum and Disturbance Level on the Growth and Stress Responses of Yellow Perch Perca flavescens

Abstract.— We evaluated the effects of different lighting spectra and routine disturbances on the growth and stress responses of yellow perch Perca, flavescens. Fish were reared in tanks under one of three different lighting spectra: blue (405–530 nm), red (600–750 nm). or full spectrum (380–750 nm). For each lighting spectrum, fish were reared under one of two disturbance levels: one in which the fish were exposed to 2–4 daily routine disturbances which typify intensive tank culture conditions (e.g., casting shadows over the tank, sham tank siphoning, and dissolved oxygen measurement: ‘disturbed’). or a second treatment in which such disturbances were minimized (‘undisturbed’). The fish were reared for 87 d under temperature, photoperiod. and feeding conditions near optimal for the growth of yellow perch. The cortisol stress response of the different fish groups was evaluated by measuring baseline serum cortisol levels on days 0, 1,3, and 21, and by measuring cortisol levels 30 min after the application of an acute handling stressor on days 0, 1, and 3. Treatment effects on growth were measured from days 21–86 of the study. On day 87, various organs and parameters were evaluated to compare the health and condition of fish reared under the different treatments. Disturbed fish gained less weight and length, and had a significantly lower condition factor than undisturbed fish. Additionally, the disturbed fish showed no signs of acclimation to the frequent disturbances. The fish under red and full spectrum light gained more length than those under blue light. Frequent disturbance had a greater negative effect on length gain in fish reared under red light than in those reared under the other light treatments. On day 21, but not on other days, baseline cortisol levels were higher in disturbed than in undisturbed fish. Undisturbed fish had higher levels of mesentery fat than disturbed fish. Our results demonstrate that yellow perch growth can be significantly affected by disturbance level and lighting conditions. These factors should be taken into consideration when developing culture strategies to maximize the growth of yellow perch reared under intensive culture conditions.     

Protection of crucian carp (Carassius auratus Gibelio) against septicaemia caused by Aeromonas hydrophila using specific egg yolk immunoglobulins

Egg yolk immunoglobulins (IgY) were obtained from laying hens immunized with inactivated Aeromonas hydrophila. The purified IgY was shown to inhibit the growth of A. hydrophila in vitro and the optimum concentration for inhibition of A. hydrophila‐specific IgY was 75 mg mL^?1. In a subsequent challenge trial, 100 carp (200~250 g) were assigned to one of ten tanks with ten carp per tank. The fish in one tank were unchallenged whereas the remaining 90 fish were injected intraperitoneally with 100 μL of A. hydrophila at a concentration of 10⁸ cfu mL^?1. For the next 21 days, all fish were moved in their respective groups to a clean tank for 20 min day^?1. The fish in four tanks (one unchallenged tank and three challenged tanks) received no treatment whereas the fish in the remaining six tanks were immersed in either 0.5 g L^?1 aqueous nonspecific IgY (N = 3) or 0.5 g L^?1 aqueous specific IgY (N = 3). Haemoglobin concentrations, white and red blood cell numbers as well as the mortality of specific IgY‐treated fish were significantly different from those of the control. These results suggest that passive immunization by immersion with pathogen‐specific IgY may provide a valuable treatment for A. hydrophila infection in carp.     

中西太平洋金枪鱼围网自由鱼群渔场重心变动及其与南方涛动指数的关系

文章根据2013—2017年中国中西太平洋金枪鱼围网船队捕捞日志,利用捕捞自由鱼群作业位置、作业时间和渔获量等数据信息,分析了自由鱼群渔场重心月间变化、年际变化与南方涛动指数(South Oscillation Index,SOI)的关系。结果显示,渔获量较高的海域海表温度(Sea surface temperature,SST)高于29℃;自由鱼群的渔场重心主要分布介于160°E—175°W;2013—2015年渔场重心有逐年向东偏移的趋势,但无明显的月间变化规律;SOI为正值时,中西太平洋“暖池”较正常年份向西偏移,自由鱼群渔场重心亦明显向西偏移;反之,自由鱼群渔场重心较正常年份向东偏移。相关性分析显示SOI和月间渔场重心的经度之间呈负相关(相关系数为?0.27,P<0.05),表明金枪鱼围网渔场变动和异常气候的发生存在密切联系。研究结果对于掌握中西太平洋金枪鱼围网渔场变动规律具有一定参考价值。     

Estimation of flow in a rearing tank of marine fish larvae by simplified numerical computation—a case of two-dimensional flow

Marine fish larvae are fragile against physical stress. However, few studies have been conducted to evaluate the flow field in a rearing tank, which is assumed to provide a high degree of physical stress to marine fish larvae. The flow field in a rearing tank (volume of 1 m³) is generated by aerators, which are commonly used to provide oxygen.

This paper is a report on the estimation of stationary flow in the rearing tank of marine fish larvae. The larvae are seven band grouper larvae of Epinephelus septemfasciatus, which have a very low survival rate immediately after the hatching of eggs. The experiments of rearing of seven band grouper larvae were carried out using rearing tanks with four aeration rates (1000, 200, 50 ml/min, and no aeration). The effects of aeration on the survival and floating death of seven band grouper larvae were examined. The experiments confirmed that the mass mortality of seven band grouper larvae depends on the flow rate in the rearing tank. Aeration at 200 ml/min resulted in the highest survival and growth rates of grouper larvae.

Larvae-rearing experiments provided evidence that the flow rates of the rearing tanks are very important design aspects of rearing tanks. The estimation of flow in a rearing tank for an aerating rate of 200 ml/min was carried out by numerical calculation. The computation was simplified by a two-dimensional flow based on experimental results. The calculated flow in the rearing tank was compared with the experimental one. The calculation of the stationary flow in the rearing tank showed good qualitative and quantitative agreement with the experimental results. The numerical estimation of the flow in a rearing tank of marine fish larvae was confirmed to be effective and satisfactory for the design of a tank that would provide optimum performance.     

拥挤胁迫后鲫鱼血液皮质醇和溶菌酶水平的变化及对病原的敏感性

分别在拥挤胁迫后第3、10、20、30天对鲫鱼(Carassiusauratus)血液皮质醇水平和血液溶菌酶水平进行了检测,并在每次采集血样后用嗜水气单胞菌(Aeromonashydrophila)进行人工感染以评估鱼体抵抗力。结果显示,血液皮质醇水平在胁迫后几天内显著升高(P<0.005),随后虽有所下降,但至第30天高密度组仍保持较高水平(216.32±11.91)ng/mL。实验初期,血液溶菌酶水平小幅升高,但经过长时间的拥挤后,高密度组血液溶菌酶活性受到极大抑制,显著低于同期对照组(P<0.01)。攻毒后的死亡率与胁迫时间成正相关,在最后一次采样期,高密度组死亡率高达58.3%,而同期对照组仅为16.7%,两者具统计学差异(P<0.01)。实验表明,经过拥挤胁迫后,鲫鱼血液皮质醇水平和溶菌酶水平均发生了变化,短期内,两者成正相关,而长期胁迫则表现为负相关。另外,拥挤胁迫也引起了鱼体抵抗力的下降。     

Progression of staining-type hypermelanosis on the blind side in normally metamorphosed juveniles and pigmentation progression in pseudoalbino juveniles of the Japanese flounder Paralichthys olivaceus using individual identification

Abnormal flounder coloration frequently occurs in flounder hatcheries and diminishes the commercial value of the fish. To understand hypermelanosis, the progression of staining-type hypermelanosis in normally metamorphosed juveniles and ocular-side pigmentation in pseudoalbino juveniles were examined in the Japanese flounder Paralichthys olivaceus. Sixty-five days post hatching, juveniles (total length, 6 cm) were individually identified by color-marker implantation, and the darkened area of the body surface was examined for 10 weeks by image analysis of digital photographs of the fish taken from above or below the transparent tank. Staining was observed to mainly begin at the upper and lower bases of the tail fin, expanded anteriorly along the peripheral part of the trunk, and ceased after 2 months. The individuals in which staining occurred earlier expressed severe staining and small body size by the end of the experiment. Further, pigmentation of the ocular side in pseudoalbino juveniles ceased after 2 months, but the order of pigmentation was different from that on the blind side. In this case, darkening began from the posterior, but expanded from the center to the periphery of the trunk. Even at the end of the experiment, ctenoid scales were exclusively found within the darkened area, together with cycloid scales.     

Measuring cultured fish swimming behaviour: first results on rainbow trout using acoustic telemetry in tanks

An experiment was conducted to measure swimming activity of rainbow trout (254.0±33.7 g) held in outdoor tanks under three culture conditions with stocking density used to generate differences: 27 (Culture Density 1, CD1), 80 (CD2) and 136 kg m⁻³ (CD3). Fish were fed dry pellets at 1% of tank biomass from 9h00 to 13h00 with automatic feeders. Using acoustic telemetry, fish positions were monitored every 5 s during 48 h for nine fish (three in each treatment). Swimming behaviour was analysed in terms of trajectories: they varied between (i) holding position (high turning angles), (ii) chaotic trajectories (equal use of all turning angles) and (iii) circular swimming (average turning angle of 60°). Space utilisation differed for each culture condition: CD3 conditions induced a prolonged residence time in the central zone of the tank. Rainbow trout swimming activity patterns and levels differed depending on both day–night alternation and culture conditions. All fish reared at CD1 and one reared at CD2 were day-active. All the other fish showed high activity pattern variability and a higher swimming level was observed under CD3. These results illustrate that monitoring fish swimming activity is feasible even under high densities and provide relevant insights on fish activity which can lead to behavioural welfare indices in relation to constraints imposed by culture conditions.     

Effect of tank proportions on survival of seven-band grouper Epinephelus septemfasciatus (Thunberg) and devil stinger Inimicus japonicus (Cuvier) larvae

We examined the effects of rearing‐tank proportions on early survival, surface death and growth of the seven‐band grouper Epinephelus septemfasciatus (Thunberg) and the devil stinger Inimicus japonicus (Cuvier). Fertilized eggs were introduced into three differently shaped 100 L rearing tanks. The three tanks had different water surface areas, and included a shallow tank (S; 71 × 26 cm in diameter and depth, respectively), an intermediate tank (I; 57 × 39 cm) and a deep tank (D; 44 × 70 cm). Both species showed their highest survival rate and the lowest numbers of surface death in the D tank (P<0.05). There were no significant differences between fish reared in the three tank shapes in notochord length, total length, growth rate and dry weight. Rearing‐tank shape affected larval movement in the water column, with the duration of larval movement under the water surface being the shortest in the D tank. These results suggest that using a rearing tank of a suitable shape could significantly reduce the surface death of marine fish larvae.     

光照颜色对虹鳟行为反应、血浆皮质醇和生化指标的影响

光照是影响鱼类行为、生理以及生长的主要环境因子之一.为研究光照颜色对虹鳟行为反应、血浆皮质醇、生化指标的影响,实验根据鱼类行为学研究方法,分别将白、红、黄、蓝和绿5种光照颜色灯带铺设在室内试验水槽中央底部,将虹鳟放置在水槽同一侧,观察虹鳟在水槽中穿越灯带尾次数及行为反应;根据行为生理学研究方法,分析比较在不同光照颜色下...     

Patchiness Formation and Development of Schooling Behavior in Pacific Threadfin Polydactylus sexfilis Reared with Different Dietary Highly Unsaturated Fatty Acid Contents

Abstract.— Nutritional condition in larval fish culture has generally been evaluated based on growth and survival, and stress tolerance by air exposure. Here we made direct observations of fish in rearing tanks to estimate the quality of the fish. Pacific threadfin Polydactylu.s sexfilis larvae were reared with rotifers and Artemia nauplii enriched with three levels of highly unsaturated fatty acids (HUFA). The three levels were defined as no-, medium-, or high-HUFA groups, in which the fatty acids emulsions contained 0, 30, or 50%. respectively. of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). The formation of patchiness (dense aggregations of fish on the surface) and development of schooling behavior were observed in four replicate rearing tanks for each feed treatment. Patchiness was formed in every tank with the highest densities of 60–250 fish/L on day 7–8 posthatch. Both medium-HUFA and high-HUFA groups showed schooling behavior at 19 d after hatching, whereas fish in the no-HUFA group did not form schools even at day 25. The body lengths of fish from each group were not significantly different, although the no-HUFA group suffered high mortality after day 20. Our results suggest that HUFA deficiency has a serious negative impact on P. sexfilis during metamorphosis rather than during the early larval stage. We also consider that direct observation rather than stress tests by air exposure may be an effective tool to measure the quality of juvenile fish.     

Comparison on growth performance,body coloration changes and stress response of juvenile river catfish,Pangasius hypophthalmus reared in different tank background colour

The effects of different tank background colours (green, black and white) on the growth performance and body coloration of juvenile river cafish, Pangasius hypophthalmus, were examined in this study. The experimental fish with an initial body weight (BW) 0.13 ± 0.05 g and total length (TL) 2.54 ± 0.37 cm were used, and groups of 15 fish per tank were randomly distributed. The experiment was conducted for 20 days as a triplicate for each treatment. Survival, growth in BW, body weight gain (BWG), total length (TL), total length gain (TLG), specific growth rate (SGR), condition factor, feed conversion ratio (FCR), swimming speed, body coloration and stress response were evaluated. River catfish reared in white and green tanks attained significantly higher BW, BWG, TL, TLG and SGR compared to the black tank. The white tank attained significantly better FCR compared to the black tank. River catfish showed the most active swimming behaviour in the green tank (5.49 ± 1.32 cm/s) while the least in the white tank (3.37 ± 0.93 cm/s). Body coloration of river catfish in the black tank showed almost pure black body coloration (75.59 ± 9.08), followed by the green tank (126.23 ± 17.46) and the white tank (148.19 ± 10.51). However, there was no significant difference in the stress level of river catfish reared in white and black tanks and insignificant to those reared in the green tank. The findings in this study showed that the white and green background colour tanks can be used for promoting growth of river catfish culture while the black background colour tank can enhance body coloration that is suitable as ornamental fish.     

Selection experiments with salmon. II. Proportion of Atlantic salmon smoltifying at 1 year of age

Salmon (Salmo salar) brood stock were taken from 37 localities in Norway for 4 consecutive years. Each year, after fertilization, the offspring in each family from each strain were reared in separate egg trays and fingerling tanks. The percentage of fish in each tank which smoltified at 1 year old was recorded, and environmental and genetic factors influencing the percentage smoltification were studied. Percentage smoltification was significantly affected by the number of fish held in a tank, or fish density (correlation coefficient 0.03–0.27). Variation between locality of origin of brood stock and per cent smoltification was highly significant for each year class, and there was a high correlation (0.89–0.95) between smolt percentage and average weight of fish in a family. Heritabilities in per cent smoltification estimated by sire component from total data had a weighted average of 0.06 (range 0.16 to ?0.01). From the dam component heritabilities ranged from 0.20 to 0.40 when tank effect was ignored, and 0.08–0.25 with tank effect taken into account. Variance components for locality were two to three times as high as those for sires within localities, indicating that genetic variation is greater between than within localities. Highly significant interaction sire × dam was found, suggesting a considerable nonadditive genetic variance influencing the percentage of fish smoltifying at 1 year of age.