Distribution patterns of saprolegniosis cutaneous lesions in wild and farmed brown trout (Salmo trutta L.) obtained using a geographic information system (GIS)

A retrospective study was conducted using 250 clinical records of brown trout (Salmo trutta L.) with saprolegniosis by Saprolegnia parasitica, which had been collected from 8 rivers and 1 fish farm in the province of León (Spain). A geographic information system (GIS) was used to obtain skin lesion distribution patterns in males and females. Lesions in wild brown trout affected 15.31 ± 13.33% of the body surface, with a mean of 12.76 ± 6.56 lesions per fish. In addition, 51.23% of wild trout presented lesions with necrosis of the skin or fins. The pattern obtained when not distinguishing between sexes indicated that saprolegniosis lesions are mainly located above the lateral line and most frequently affect the dorsal cephalic region, the adipose fin, the peduncle and the caudal fin. However, differences were observed between males and females. Farmed trout presented a lower percentage of affected body surface (2.06 ± 4.36) and a lower number of lesions with and without necrosis because they received preventive treatment for saprolegniosis.     

A Survey of Trout Fin Erosion, Water Quality, and Rearing Conditions at State Fish Hatcheries in Utah

A total of 600 hatchery trout were examined for signs of fin erosion including rainbow trout Oncorhynchus mykiss , cutthroat trout O. clarki , brook trout Salvelinus fontinalis and brown trout Salmo trutta . A scoring system was used to evaluate erosion on all fins from 20 fish samples. Water quality and hatchery rearing variables were also determined for corresponding raceways or ponds. For rainbow trout groups ( N = 24), stepwise multiple linear regression was used to interpret the relationship between fin erosion and the other variables. These fish groups averaged between 92 and 243 mm in total length and no significant correlation was observed between length and a fin erosion index ( r = 0.045). The best-fit regression model (adjusted R² = 0.689) suggested that fin erosion was correlated with lower alkalinities, unnatural bottom substrates (concrete or steel), higher unionized ammonia levels, and higher fish densities. Despite significant variation between hatcheries, fin condition was significantly better in rainbow trout than in cutthroat trout in three of four hatcheries containing both species and the same substrate. Fin erosion in rainbow trout occurred primarily on dorsal fins, followed in order of decreasing severity, by pectoral, caudal, anal, and ventral fins.     

Effects of baffles and isolation on dorsal fin erosion in steelhead trout, Oncorhynchus mykiss (Walbaum)

Abstract. Dorsal fin condition was evaluated in two groups of hatchery-reared steelhead trout, Oncorhynchus mykiss (Walbaum), and compared to wild fish. Hatchery fish were reared either in nursery tanks with baffles or in isolation (1 fish/rearing space). Evaluations were conducted to determine differences in dorsal fin condition between these groups and to monitor the progression and severity of fin damage. Isolated hatchery and wild steelhead trout maintained perfect dorsal fins with characteristic white margins. Hatchery fish reared in nursery tanks with baffles experienced dorsal fin erosion that started when the fish were about 40mm total length (30 days after being on feed). This erosion continued until dorsal fin length averaged only 2·3 mm in fish 161–200 mm total length in contrast to an average dorsal fin length of 20·9mm in wild fish of the same size.     

Fin development in stream- and hatchery-reared Atlantic salmon

To determine the effect of development and environment on fin growth, we measured fin lengths of juvenile Atlantic salmon (Salmo salar) from two hatcheries (August, October and April–May), stream-reared fish (July and October) stocked as fry into two tributaries, and smolts from the main stem of the Connecticut River (May). For stream-reared parr, there was a linear relationship between the dorsal, caudal and anal fins with fork length, while the pectoral, pelvic and adipose fins exhibited a curvilinear relationship with fork length. Parr from a high gradient stream had larger caudal fins than fish from a low gradient stream, but other fins did not differ. Regression lines for the fins of stream-reared smolts were all linear when fin length was regressed against fork length. Stream-reared parr had larger pectoral, pelvic and anal fins than smolts of similar size while dorsal and caudal fin lengths did not differ. Regression equations formulated using the fins of stream-reared parr were used to calculate the percent difference (100×observed fin length/expected) in fin lengths between stream- and hatchery-reared parr. The pelvic, adipose, caudal and anal fins of hatchery-reared parr showed no signs of degeneration by the first sampling period 7 months after hatching, whereas degeneration in the pectoral (13–20%) and dorsal (15–18%) fins was evident at this time. By the end of the study, degeneration was present in every fin except the adipose, with the pectoral (35–65%) and dorsal (32–58%) fins exhibiting the greatest amount of fin loss. All fins of hatchery-reared parr became shorter with time. There were minor differences in fin degeneration among parr from the two hatcheries, but the overall pattern of decreasing fin size was similar, indicating a common cause of fin degeneration. Comparison of stream- and hatchery-reared fish is a valuable means of determining the impact of captive environments on fin growth.     

Frequency and distribution patterns of Saprolegnia infection in wild and hatchery-reared brown trout Salmo trutta L. and char Salvelinus alpinus (L.)

Abstract. Fungal infection of sexually mature brown trout and char was associated with a particular type of Saprolegnia exhibiting a low degree of homothallic sexuality. Hatchery-reared brown trout were more severely infected (in terms of the % area of the body covered with the fungus) than were wild fish. The fins of hatchery-reared fish were particularly prone to Saprolegnia infection regardless of sex. In wild brown trout, a sexual difference in the pattern of infection was demonstrated. The flanks of the male fish appeared to be more prone to infection when compared with the female and there was a greater susceptibility of the caudal and ventral fin of the female when compared with the male. Evidence is presented which suggests that the incidence of infection in mature male salmonid fish prior to spawning is significantly greater than in the females. This difference may not be apparent in spent fish after spawning. These findings are discussed in relation to the background concentration of fungal spores in the water, the behavioural characteristics of spawning fish and differences in epidermal structure.     

Effects of different kinds of fin-clipping on over-winter survival and growth of fingerling brown trout, Salmo trutta L., stocked in small streams in Norway

Abstract. Nine thousand fingerling (0+) brown trout, Salmo trutta L., (size 50–90 mm) were fin-clipped in six different ways and released in small streams in September 1984 and 1985. A total of 2625 fish were recaptured by electrofishing the year after stocking. Differences in survival between fin-clip groups were found in one out of eight stockings. No growth differences were found among the several groups. Pectoral and anal fins regenerated most, while adipose fins regenerated least. Single fin-clipping is a recommended marking method for fingerling brown trout during short-term studies. Multiple fin-clips may result in lower survival. Regeneration of fins, especially pectoral and anal fins, make the clipping of these fins less adapted to long-term investigations.     

Repeatability of fin length measurements using digital image analysis and studies of fin erosion as indicator of social interactions in Atlantic cod (Gadus morhua)

The aims of this study were to examine fin erosion caused by social interactions between Atlantic cod (Gadus morhua) juveniles, and to evaluate the repeatability of recorded fin length using digital image analysis (DIA). Fin length of 2100 juvenile Atlantic cod was analysed using DIA, during a 6 weeks experiment. The lengths of the three dorsal fins and the caudal fin were measured by three different assessors (M, K, B) three times during the experiment. Repeatability was based on a sub set of data from 42 randomly chosen fish. Assessor M measured the length of the fins of the 42 fish three times (M1, M2, M3). M1 and M2 were done on the same day, while M3 was conducted 2 weeks later. Assessor K measured two times with a 2‐year interval, and assessor B measured the fin length only once. The correlations between replicated measurements within assessor were highest for assessor M measured on the same day indicating an effect of memory. Repeatability of fin length ranged from 0.57 to 0.73 for the four fins. Social interaction with respect to fin erosion was studied using data on the four fins from all 2100 fish. ‘Relative fin length’ (fin length/total body length × 100) was calculated to assess fin erosion. Results indicated that all four fins were eroded due to social interactions, but the caudal fin was most severely eroded. In conclusion, DIA can be used to measured fin length but the method could be improved by using chromatic pictures.     

The commercial exploitation of sea trout, Salmo trutta L.

Abstract. The net and coble catch of sea trout in the River North Esk was sampled between 1977 and 1979. A comparison of the length frequency distribution of these samples with those of sea trout taken in a trap which was assumed to be unselective revealed that the net and coble fishery was very selective. Only isolated fish below 35·0 cm were encountered in the commercial catch samples, yet between 25% and 41% of the upstream migratory sea trout taken in the trap during the netting season were below this length. The sea trout in the commercial catch samples were predominantly maiden, one-sea-winter fish. The dominant age class each year was the 2·1 + group, 3·1 + fish comprising the other major age class. The freshwater age of the maiden sea trout sampled declined as the season progressed. The proportion of previously spawned fish in the samples ranged between years from 12% to 15%. The mean length and mean weight of sea trout sampled from each year's catch showed little variation, ranging from 42·9 cm to 43·3 cm and 971 g to 972 g, respectively. The ratio of males to females in the 1979 sample was 1·00:2·18. The use of morphometric characteristics, including head length, pectoral fin length and adipose fin length was investigated with the aim of distinguishing the sex of fish taken early in the season from external features alone. Although in each month the mean head length as a percentage of fork length of males was greater than that of females, this difference was not sufficient to enable the rapid determination of sex during commercial catch sampling routines. The exploitation rate of sea trout reaching the most upstream major fishing station, Morphie Dyke, was estimated from the recapture of upstream adult sea trout removed from a trap and released in the main river 2 km downstream of Morphie Dyke. The percentage exploitation rate at this fishing station was found to range between 6·4% and 12·2%, and the percentage exploitation rate for the entire net and coble fishery was at a level of approximately 30% during the period of the study. The sea trout statistics of the North Esk net and coble fishery for the period 1925–1979 were examined, and the effect of a change in fishing effort on these figures is described. Recent catch figures, although below those reported during the mid-1960s, are above the level of catches reported prior to 1952.     

The Effects of Fry Rearing Density on Hatchery Performance, Fin Condition, and Agonistic Behavior of Rainbow Trout Oncorhynchus mykiss Fry

Rainbow trout Oncorhynchus mykiss fry were reared at four densities ranging from 10,800 to 43,926 fish/m³ (9.91 to 37.60 kg/m³) during an initial feeding period of 35 d. Each of the four initial density treatments were then split into high (3,780 fish/m³) and low (1,890 fish/m³) density groups and reared in outdoor raceways for an additional 74 d. A necropsy-based general health and condition assessment indicated that hematocrit, plasma protein, and the thymus index were significantly elevated in the outdoor high density group. Changes in these variables were unrelated to the initial rearing density, except for plasma protein which decreased as the initial density increased at low densities. Other necropsy variables indicated normal, healthy fish. Agonistic behavior was assessed at 4, 9 and 13 wk of age by observing the number of aggressive chases in paired and group (five fish) trials. The number of chases generally increased with age, although the difference between 9 and 13 wk was variable. Feeding did not elicit more chases in this study except for 9-wk-old fry. Initial rearing density did not have any impact on the number of chases at 4 or 13 wk, but at 9 wk the number of chases increased with initial density for the group tests. Relative fin length measurements of all fins except the adipose indicated no combination of initial density and outdoor density was superior to another for reducing fin erosion. This study indicated that rainbow trout fry may be reared at initial densities approaching 44,000 fish/m³ (Piper density index of 1.1) without negatively affecting growth and fin condition or inducing higher levels of agonistic behavior later on.     

Effect of Light Intensity on Color Performance of False Clownfish,Amphiprion ocellaris Cuvier

Color performance of false clownfish, Amphiprion ocellaris Cuvier, was examined under three levels of light intensity (20–50 , 600–850 , and 2700–3500 lx) for 5 wk. The experiment was conducted in nine rectangular glass aquaria (25 × 25 × 20 cm) with three replicates. Each aquarium was stocked with 36 fish, and 3 fish were randomly sampled from each aquarium every other week. Digital images were taken weekly on each individual fish after it was anesthetized in MS‐222. The color performance in hue, saturation, and brightness was quantified using image analysis. In addition to the whole‐body analysis, each fish image was divided into ventral and dorsal parts to assess the body position‐dependent effect. Furthermore, color differences between dorsal fin, anal fin, ventral fin, and caudal fin were also quantified. The whole body was brighter at low light than at medium or at high light intensity. Irrespective of light intensity, the dorsal side was more orange but less bright than the ventral side. Brighter light strengthened overall orange color on fish fins. The dorsal fin and ventral fins appeared more orange than the anal and caudal fins regardless of light intensity and exposure duration. Similar to body color, low light also led to brighter fins, especially for caudal and dorsal fins. Our results indicate that ambient light could regulate fish color performance but could not change the pigment dominance by β‐carotene. Light intensity is unlikely to change the contrast between dorsal and ventral sides, but dim light tends to make fish body brighter, and bright light strengthens orange color on fins.     

Effects of temperature on feed intake and plasma chemistry after exhaustive exercise in triploid brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis> L)

The physiological effect of temperature on feed intake and haematological parameters after exhaustive swimming in diploid and triploid brown trout (Salmo trutta) was investigated. Trout were exposed to an incremental temperature challenge (2 °C/day) from ambient (6 °C) to either 10 or 19 °C. Feed intake profiles did not differ between ploidy at 10 °C; however, triploids had a significantly higher total feed intake at 19 °C. After 24 days, each temperature–ploidy group was exposed to exhaustive swimming for 10 min. The haematological response differed between ploidy, with the magnitude of the response affected by temperature and ploidy. Post-exercise, acid–base and ionic differences were observed. Plasma lactate increased significantly from rest for both temperature and ploidy groups, but glucose increased significantly at higher temperature. Post-exercise, triploids at 19 °C had significantly higher osmolality and cholesterol than diploids, but differences were resumed within 4 h. Elevated alkaline phosphatase (ALP) and aspartate aminotransferase (AST) in fish at higher temperature suggested greater tissue damage; however, both ploidy responded similarly. Despite no significant differences in deformity prevalence, the type and location of deformities observed differed between ploidy (decreased intervertebral space with higher prevalence in tail area and fin regions for diploids, while vertebral compression, fusion in cranial and caudal trunks for triploids). These results suggest triploids have greater appetite than diploids at elevated temperature and that triploids suffer similar blood disturbances after exercise as diploids. These findings have implications for the management of freshwater ecosystems and suggest that stocking triploid brown trout may offer an alternative to diploid brown trout.     

The effect of domestication on a brown trout (Salmo trutta m fario) broodstock in Hungary

Molecular markers (PCR–RFLP and microsatellite) were used to investigate the genetic background of the only brown trout (Salmo trutta m fario) broodstock in Hungary which due to the hydrogeography of the country should theoretically belong to the Danubian lineage. PCR–RFLP (mitochondrial DNA control region and lactate dehydrogenase and somatolactin genes) as well as microsatellite (BFRO002, OMM1064, Ssa408uos, SsoSL417, SsoSL438) markers were used to distinguish between Danubian and Atlantic lineages of brown trout in the Lillafüred broodstock. Altogether 435 fish were tagged during the experimental period. Due to mortalities, fin clips were collected from 401 individuals. According to the genetic analysis of the mitochondrial DNA, the Danubian haplotype is present in only one individual (0.2 %) of the broodstock. Analysis of the nuclear markers revealed that alleles characteristic of both the Atlantic and the Danubian lineages are found in the population. However, Atlantic alleles dominate throughout the broodstock which is in Hardy–Weinberg equilibrium according to the investigated markers. Results indicate that the original broodstock that was introduced to the farm following its construction in 1933 was of the Atlantic lineage. Although later fish from a local stream were collected and added to the broodstock, the number of these was limited and they were almost exclusively males. Fish from this farm that are stocked by anglers can have a significant genetic impact on trout populations of natural streams.     

Fin damage and growth parameters relative to stocking density and feeding method in intensively cultured European perch (Perca fluviatilis L.)

We evaluated the relationship of stocking density to survival, growth performance and fin condition of European perch Perca fluviatilis with hand feeding and self-feeders. Hand-fed perch (body weight 19.1 ± 5.1 g and total length 107 ± 9 mm) were reared at 0.5, 1.0, 1.5 and 2.0 fish/L. Self-feeding perch (body weight 25.4 ± 3.9 g and total length 128 ± 7 mm) were reared at stocking densities of 0.6, 1.0 and 1.4 fish/L. Pond-reared perch served as a comparison group for fin damage assessment. We found no differences in survival rate among stocking densities with either feeding method. Hand-fed fish displayed the highest weight gain and SGR at stocking density of 0.5 fish/L. The self-feeding fish showed a non-linear association of weight gain with stocking density with the highest growth at 1.0 fish/L. Fin length was noticeably greater in pond-reared fish compared with RAS-reared fish regardless of feeding method. In both experiments, fin length relative to standard length showed a negative relationship with stocking density, with pectoral fins showing the greatest effect. Fin condition deteriorated with increasing stocking density, and growth was highest at 0.5 and 1.0 fish/L in hand-fed and self-feeding fish, respectively.     

Ultrasound evaluation of the gonadal structure in sex-reversed rainbow trout females

Ultrasound approach has been used to assess morphology of the gonadal structure in the sex-reversed rainbow trout females (neomales) provided in the course of 11β-hydroxyandrostenedione treatment applied within gonadal differentiation period. Eighteen matured individuals (in range 38.0–48.6 cm of body length and 802–1644 g of body weight) were scanned using digital ultrasound apparatus (DP-6900 model) Mindray Ltd., during the spawning season. After screening, fishes were killed to validate the morphological configuration and position of the gonads in the body cavity. The favorable place for cross-sectional imaging of gonadal lobes was half of the distance between the pectoral and pelvic fins below lateral line of neomales. Most of the examined specimens (61 %) had properly shaped, paired testis. Moreover, presence of individuals with asymmetrical gonads (33 %) and one bisexual fish was confirmed. There were no differences between total volume of sampled semen and sperm motility, but statistically significantly different in sperm concentration within selected (with symmetrical and asymmetrical testis) groups of neomales. It was confirmed that ultrasonic imaging is an efficient and accurate method to determine the state of gonads of mature sex-reversed rainbow trout females during spawning season and offers the opportunity for non-invasive detection of any morphological anomalies in their gonads.     

Resource use of native and stocked brown trout Salmo trutta L., in a subarctic lake

Habitat use, food composition and growth of stocked and native brown trout, Salmo trutta L., were studied in the subarctic Lake Muddusjärvi in northern Finland. Stocked brown trout and native brown trout preferred littoral and pelagic areas. Trout were stocked in October. In June stocked trout fed primarily on invertebrates while native fish were piscivorous. From July onwards the composition of the diet of both stocked and native trout was similar and consisted almost entirely of small‐sized whitefish. Brown trout were already piscivorous at a length of about 20 cm. The mean length of prey consumed was about 12 cm. Mean length‐at‐age was similar from the second year in the lake despite of the larger size of stocked fish during the first year in the lake.     

Comparison of pelvic fin rays, scales and otoliths for estimating age and growth of bull trout, Salvelinus confluentus

Abstract  The suitability of three anatomical structures to determine age and growth of bull trout, Salvelinus confluentus (Suckley), was assessed. Scales and pelvic fin rays collected from recaptured bull trout 96–265 mm TL were used to validate annulus formation and assess the accuracy and precision of back calculation. Ageing precision and agreement of assigned ages were compared among scales, fin rays and otoliths from bull trout 52–711 mm TL. Annulus formation was validated for 88% (14 of 16 fish) of recaptured bull trout using pelvic fin rays and 68% using scales (15 of 22 fish). Annulus formation in fin rays occurred between late April to early June, and the hyaline (non-growth) band began forming in late August. Back-calculated length was not significantly different from measured length at initial capture either for fin rays or scales ( P  ≥   0.19), and absolute percent error was 7.2 ± 1.2 (mean ± SE; n  =   14) for fin rays and 8.7 ± 1.9 ( n  =   15) for scales. Consistency of back-calculated lengths at age between tag and recapture samples for individual fish was similar for fin rays (mean absolute difference = 8.2% ± 0.9; n  =   33) and scales (9.4% ± 1.4; n  =   40). However, fin rays (87% precision) and otoliths (90%) provided notably higher ageing precision than scales (68%) and closer agreement of assigned ages, particularly for fish older than age 4. Pelvic fin rays appear to offer more accurate and precise age and growth determinations than scales and a non-lethal alternative to otoliths, but further work is needed to validate the accuracy and precision of ageing large, migratory bull trout.     

虹鳟肠炎红嘴病病理模型的构建

为探讨鲁氏耶尔森菌侵染虹鳟的致病机制,本实验建立了鲁氏耶尔森菌感染虹鳟引起的肠炎红嘴病的病理模型,制定相应的临床症状及组织病理学评分系统,并对该模型进行研究。将43尾平均体质量约为12 g的健康虹鳟随机分成5组:3个实验组(n=30)、对照组(n=10)和哨兵组(n=3)。3个实验组分别采用2.0×106、2.0×107和2.0×108 CFU/m L的鲁氏耶尔森菌感染浓度,通过腹腔注射方式进行人工感染试验。对感染鲁氏耶尔森菌的虹鳟肠、肝脏、脾脏和肾脏组织进行镜检及临床症状、剖检病变判断,结合细菌学检测,按制定的评分系统评价各组肠炎红嘴病造模效果,确定最佳造模方案。结果显示,各攻毒组虹鳟感染后72 h均出现不同程度死亡,临床症状表现为红嘴、肛门红肿、鳍(胸鳍、腹鳍、臀鳍)等出现不同程度充血,下颌部、腹部出现出血点等。组织病理学可见肝脏、脾脏、肾脏及肠组织均有炎性细胞浸润现象出现,肝细胞、肠上皮细胞和肾小管上皮细胞等实质细胞变性、坏死,脾脏部位淋巴细胞减少、红细胞死亡堆积。综合各组得分发现,2.0×107 CFU/m L组的鲁氏耶尔森菌感染虹鳟造模效果最佳,患病虹鳟的临床症状显著且组内差异较小,病程迁延较长,便于研究。研究表明,对体质量约12 g的虹鳟幼鱼腹腔注射0.1 m L浓度为2.0×107 CFU/m L的鲁氏耶尔森菌可成功构建肠炎红嘴病病理模型。     

Assessment of Demand Feeder Spacing on Hatchery Performance, Fin Condition, and Size Variation of Rainbow Trout Oncorhynchus mykiss

Abstract.— Fingerling rainbow trout, Oncorhynchus mykiss , were fed for 133 d by one of three feeding methods: one demand feeder per 5.5 m of raceway, 2 demand feeders per 5.5 m of raceway, and hand-fed controls. Mean weight, total length, mortality, and feed conversion were not influenced by the method of feeding. Size variation did not differ among treatment groups, as assessed by comparing the coefficient of variation of total length. Necropsy-based health and condition profiles were conducted three times during the rearing period, and results indicated that fish were generally normal and healthy in all treatments. Several parameters differed significantly over time, but no trends were observed except for the fin index and hematocrit. Over time, hematocrit decreased from 48.6 to 45.0%, and the fin index increased from 0.80 to 1.57. Fin index values did not differ among the feeding methods. Fin condition assessed by measuring relative fin length was better in the single feeder treatment than controls for caudal and ventral fins in the last sample. However, since fish from the two-feeder treatment did not differ from controls, demand feeding per se did not improve fin condition relative to fish that were fed by hand, four to six times per day. The lack of significant improvements in growth or health with the addition of another demand feeder indicated that using more than one feeder per 5.5 m of raceway length is unnecessary for culture of juvenile rainbow trout.     

Melamine–cyanurate complexes and oxidative stress markers in trout kidney following melamine and cyanuric acid long-term co-exposure and withdrawal

In 2007, renal failure and death in pets were linked to pet food containing both melamine (MEL) and cyanuric acid (CYA). In mammals and fish, the co-administration of MEL and CYA causes renal crystal formation. Moreover, little is known about the process of crystal removal in fish. The aim of this study was to evaluate the formation of MEL–cyanurate crystals in kidney of rainbow trout (Oncorhynchus mykiss) fed combined MEL and CYA diets for 10 weeks at 250, 500 and 1,000 mg/kg in feed (equivalent to 2.5, 5, 10 mg/kg body weight of trout fed 1 % body weight per day). During the exposure trial and throughout a withdrawal period, prooxidant effects of MEL and CYA were evaluated on oxidative stress markers such as catalase, glutathione S-transferase and malondialdehyde. Crystal formation was dose and time dependent, and after six withdrawal weeks, crystals persisted in kidney of trout treated the highest triazine dose. Catalase and glutathione S-transferase activity in kidney of trout exposed to both triazines for 10 weeks indicated that MEL (with or without CYA) can exert a higher prooxidant effect than CYA dispensed singly. Although the enzymes activity increase appears to be reverted after two MEL withdrawal weeks, persistence of crystals may lead to severe damage in renal cells of fish.     

Niacin requirement for optimum growth, feed conversion and protection of rainbow trout, Salmo gairdneri Richardson, from ultraviolet-B irradiation

Triplicate groups of 75 rainbow trout, Salmo gairdneri Richardson, (mean weight 0–76 g) were fed a semipurified diet containing added niacinamide in amounts of 0.0, 1.25, 2.5. 5, 10, 20, 40, 80 or 160 mg/kg diet (ppm), for 16 weeks to determine the amount of niacinamide needed for optimum growth, feed conversion, and prevention of dermatopathy induced by UV light. At the end of the study, fish were exposed to a 275-W sun lamp limiting in the UV-B spectrum (280–360 UV) for 20h. Trout fed no supplemental niacinamide grew significantly slower than all other fish. Growth increased with each niacinamide increment through 10ppm. but not at higher increments. Feed conversion paralleled growth response to niacinamide. Exposure to UV light induced dermal lesions in trout fed less than 10ppm niacinamide. Initially, focal white spots appeared anterior to the dorsal fin, and caudal and pectoral fins became depigmented and translucent. Later, extensive erosion in caudal and pectoral fins was accompanied by desquamation of the epidermis and underlying tissues of the caudal peduncle, head and snout. Results indicated that rainbow trout need at least 10ppm niacinamide for optimum growth, feed conversion and protection against 'sunburn’caused by UV light.