© 2005 International Council for the Exploration of the Sea
Growth, survival, diet, and on-growing husbandry of haddock Melanogrammus aeglefinus in tanks and netpens
a Viking Ardtoe Marine Laboratory Acharacle, Argyll PH36 4LD, Scotland, UK
b EWOS Innovation Dirdal, Norway
c Mainstream Scotland Isle of Gigha Pumpashore, Argyll, Scotland, UK
*Correspondence to J. W. Treasurer: tel: +44 01397 875000; fax: +44 01397 875001. e-mail: jim.treasurer{at}vikingfish.com.
Growth of haddock (Melanogrammus aeglefinus) was assessed in onshore tanks in West Scotland. Fish were stocked at a mean weight of 15 g in July 2002, with a second stocking in October 2002 at 25 g. Fish had a mean weight of 755 ± 150 (s.d.) g at 20 months after stocking and were harvested. The specific growth rate of haddock was similar to Atlantic cod (Gadus morhua) during the first year but decreased by 20% after that. Liver biomass was 17.6% of the whole body weight, suggesting haddock had difficulty in utilizing dietary lipid. Reduced lipid levels in the diet had only a short-term effect on hepatosomatic index (HSI). Haddock that were held under 24-h light from the first summer solstice did not mature at an age of two years when compared with complete maturation of fish reared under ambient light. Mortality during the on-growing stage was high (28% of stock) and was attributed to Vibrio anguillarum infection, and possibly to enlarged livers. An assessment of quality found taste and texture to be as good or equal to wild North Sea haddock, and quality was improved with a five-day starvation period. Haddock mean weight, six months after transfer to netpens, was not significantly different from that of fish of the same age grown in tanks.
Keywords: cod, growth, haddock, hepatosomatic index, liver, maturation, Melanogrammus aeglefinus, on-growing, photoperiod control
Received 21 September 2004; accepted 24 November 2005.
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Introduction |
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 Top Introduction Material and methodsResultsDiscussionReferences |
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Currently, much attention is being focused on the rearing of cod (Gadus morhua) (Roselund and Skretting, 2006), and many of the technical constraints to juvenile cod production have been addressed (Hamre, 2006; Bricknell et al., 2006; Karlsen et al., 2006). There is also interest in further diversification of farming of cold-water marine finfish. Haddock (Melanogrammus aeglefinus) was identified as a leading candidate for aquaculture diversification in the UK (Treasurer, 2003), as it is the third most popular species consumed in the UK with a market share of around 43 000 t. This potential, together with declining catches of haddock in the North Sea in the late 1990s, led to a full food chain partnership and demonstration project on the farming of haddock (Treasurer, 2003). Haddock is considered a superior culinary fish to cod in parts of Atlantic Canada, the USA, and in Scotland. Interest in the current project stemmed mainly from processing and retail sector concerns about the decline in North Sea haddock landings in the UK to only 43 000 t in 2002 from a maximum of 95 000 t in 1992 (Department for Environment Food and Rural Affairs, unpublished). Landings in the North Atlantic have declined generally in the last 40 years, and the species is classified as vulnerable (IUCN, 2002).
Development of haddock aquaculture has occurred mainly in Canada (Downing and Litvak, 1999; Aiken, 2003), where research has been carried out on parental effects and environmental conditions in the hatchery period (Downing and Litvak, 1999, 2000, 2001; Buckley et al., 2000; Downing, 2002; Trippel and Neil, 2003; Rideout et al., 2004a, b), the effects of photothermal manipulation on reproductive development (Martin-Robichaud and Berlinsky, 2004), live and particulate feed requirements (Hamlin and Kling, 2001; Kim and Lall, 2001), and dietary nutrient requirements (Nanton et al., 2001; Lall et al., 2003). However, the on-growing performance of haddock has not received much attention, although fish have been farmed in netpens by Heritage Aquaculture Limited in Canada; up to 50 t of skinless, boneless fillets were marketed and sold in Canada and the USA per annum between 2000 and 2005 (A. S. Lall, pers. comm.). A recent initiative addressed the feasibility of growing haddock and cod in submerged sea cages off New Hampshire (Chambers and Howell, 2006). The present contribution examines the on-growing performance of haddock in tanks and netpens in Scotland, specifically the rearing conditions, growth, diet, feed conversion ratio (FCR), maturation, and survival of haddock over a two-year production cycle under commercial conditions.
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Material and methods |
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Rearing conditions and sampling regime
Haddock were initially reared at the Ardtoe Marine hatchery (Treasurer, 2003), and 17 000 juveniles were transferred (at 12–17 g) to a land-based tank farm on the Isle of Gigha, near the Mull of Kintyre, in July and October 2002. Fish were initially stocked in six glassfibre tanks (5.5-m diameter, 1-m depth, and 24-m3 volume) covered by shading material with high densities of 10–47 kg m–3. The temperature range was 7–17°C, salinity was 32–34, and oxygen concentration was 7.2–8.3 mg l–1 (Table 1). On 10 June 2003, ten months after transfer to the farm, the fish were vaccinated by intra-peritoneal injection to protect against Vibrio anguillarum (AVL, Schering Plough), and densities were reduced to 8–17 kg by transfer to large concrete tanks of 12-m diameter and 1.5-m depth (170 m3). Three RovscanTM submerged lights were used in each tank from the first summer solstice to retard maturation. Haddock were not graded during production, and there were no signs of aggression. Fish were harvested in June 2004, 22 months after stocking.
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A subsample of 50 fish was bulk weighed monthly, of which 25 were sacrificed for detailed measurements. The growth rates of haddock were compared with cod stocked in July 2002 at 15-g mean weight in 24-m3 tanks at the same farm from the same source hatchery. Dead fish were removed from the tanks daily and reported as numbers of mortalities per month, and as a percentage of stock size.
Feeding regimes
Fish were fed EWOS Marine diet (14% lipid) with pellet size increasing from 2 mm on stocking to 5 mm for fish of 150–300 g, 7 mm for 800-g fish, and 10-mm pellet size for heavier fish. Food was applied by hand, two to three times daily for the first three months after transfer, and once daily until the fish attained a mean weight of 300 g. Thereafter, on indications of elevated liver weights, fish were fed every second day. Feeding rate as a percentage of body weight was around 0.5% until fish were 300 g, declining to 0.2% from 450 to 700 g mean weight (Figure 1).
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Feeding regime experiments
From husbandry observations of haddock broodstock (L. Ford, pers. obs.), it appeared that feeding haddock every third day slowed the rate of liver accumulation, and so fish were fed every second day in the beginning of April 2003. Alternative feeding regimes were examined experimentally at the Ardtoe hatchery by feeding different groups of fish daily or every second or third day, over a 12-week trial period, with three replicate tanks per regime. Fish of 64–67-g mean weight were stocked in 1.5-m diameter tanks of 600-l volume, with 34 fish per tank. The flow rate was 20 l min–1, water temperature 7–10°C and continuous lighting provided 900 lux. Fish were sedated in 5 ppm metomidate, fork length and wet weight measured, and fish identified with pit tags prior to acclimation for ten days in the tanks. A diet of EWOS Marine (5 mm) was hand fed and the amount recorded. Waste pellets were siphoned from the tanks, and the weight of excess food was calculated from tables relating pellet number to weight. An initial sample of five fish from each tank was sacrificed, and the hepatosomatic index calculated, HSI = (liver weight/body weight) x 100. Fish were sedated and measured after six weeks and rotated to another adjacent 600-l tank to reduce any tank effects on fish performance. All fish in this feeding periodicity experiment were sacrificed at 12 weeks, and length, whole body, and liver weight measured. Performance was expressed as increment in body weight (g), specific growth rate from ((ln FBW – ln IBW) x 100)/d, where FBW = final body weight, IBW = initial body weight, and d = number of days, and food conversion rate from (FI/BI), where FI = food ingested by the stock and BI = biomass increment. The thermal growth coefficient TGC was also calculated as [(Mn0.33 – Mn – 10.33)/(d x temp)] x 1000, where Mn = mass at a measured point (g) and d = duration (days) for the growth period.
Retarding maturation
Lights were used in an attempt to delay maturation from the first summer solstice (21 June 2003). Three submerged lights (Rovscan) of 400 W were installed at 75-cm midwater depth, giving a light intensity of 50 lux at the tank edge (SkyeSystems Light Meter). Maturation of the fish on continuous lighting at the land-based farm on the Isle of Gigha was compared with haddock of similar age and weight at the Ardtoe hatchery held on an ambient light regime. On 24 May 2004, 150 fish exposed to 24-h light were examined and compared with 20 fish on the ambient regime. The stage of maturation, gonad weights, and GSI were determined (gonad weight/body weight) x 100.
Performance in netpens
In all, 3000 haddock of 45-g mean weight, which had been vaccinated previously by intra-peritoneal injection with Vibrio vaccine (AVL), were transferred from Ardtoe to a 12-m square x 3-m depth netpen in Shetland in October 2003, on a farm belonging to Johnson Seafarms. A further 7500 haddock of 41-g mean weight were transferred in November to Finfish Farms in Northwest Scotland and stocked in one 12-m square x 3-m depth pen. The range in seawater temperature on both farms was 6–16°C, and salinity was from 32 to 34. Netpens at both locations received ambient natural light levels, and no light treatments were applied.
Quality assessment
Tank-reared fish with no starvation period were assessed by a panel for taste, texture, and quality in August 2003 and compared with fresh, line-caught wild haddock from Iceland and net-captured fish from the North Sea. Fillet yield as headless, gutted, and boneless was assessed as a percentage of whole body weight.
Statistical analysis
Growth was expressed as the mean weights of 25 fish sampled from each tank at random by sweep net each month. Data were tested by Bartlett's test for homogeneity of variance and tested by Student's t-test with significance accepted at the 0.05 level. Where data were not normally distributed, data were transformed to common logarithm values before testing. Mean weight, FCR, and SGR in fish fed daily or every second and third days were compared by ANOVA, and post hoc comparisons were made with Tukey's HSD test.
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Results |
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TopIntroductionMaterial and methodsResultsDiscussionReferences |
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Growth and FCR
Prior to harvest in May 2004, there was no significant difference in the mean weight of fish stocked in tanks in July 2002 (752 ± 50 (s.d.) g) and in October 2002 (755 ± 148 g) (t = 0.23, p = 0.82) (Figure 2). At harvest, the mean lengths of fish from the July and October stockings were 361 ± 3 and 357 ± 3 (s.d.) mm, respectively, and the pooled value was 358 ± 3 (s.d.) mm. The mean pooled weight of males (764 g) was not significantly different from females (768 g) (t = 0.068, p = 0.946). The size distribution of fish on harvest varied greatly, from 350 to 1050 g (Figure 3), although there were no signs of aggression between fish of different sizes.
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The growth of haddock was similar to cod in the first year on the same farm but was lower than cod in the second year (Figure 4). SGR for haddock stocked on both dates was initially about 1, and comparable with cod in the same 24-m3 tanks at similar stocking densities of 12–46 kg m–3 through the first six months (Figure 5) but, after haddock attained a size of 200–300 g one year after stocking, haddock SGR dropped significantly (paired t = 3.95, p = 0.008) in comparison with cod. Only limited data are available for cod, namely for the first eight months of production, because the fish died following a tank blockage. The thermal growth coefficient of haddock in tanks was 1.54 but declined after nine months in the netpens to 0.82 and remained around that figure for the second year. The food conversion of haddock was approximately 1 until the end of the first year in tanks (Figure 6).
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Hepatosomatic indices
Enlarged livers were observed at an early stage in the study and were conspicuous from the end of the first year. For example, the HSI in November of the second year was 12–31% for a mean fish weight of 400 g with a mean HSI of 16.4 ± 3.6% (Figure 7). The regression analysis of hepatosomatic index against body weight was HSI = 15.2 + 0.0023 x BW. The slope is essentially flat, and the correlation coefficient was not significant (r = 0.08, p > 0.05). However, the HSI increased over the production cycle, and was correlated with time for both July and October stocked fish (Figure 8) (r = 0.92 and 0.94, p < 0.001). The increment in HSI was therefore time-dependent rather than related to the increase in fish mass.
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The lipid level in the diet was reduced from 14% to 12% in May 2003 in an attempt to alleviate the problem of enlarged livers and, although HSI was relatively unchanged from June to October 2003, the HSI continued to increase thereafter (Figure 9).
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Experimental feeding regimes
There was no significant difference in SGR between feeding haddock daily or every second day or third day, with mean values of 1.02%, 1.02%, and 1.05%, respectively (Figure 10) (Tukey, F = 1.44, p = 0.18). FCR was lower when fish were fed every third day (0.6) compared with 0.9–1.0 when fed every day or second day, although the difference was not significant (F = 1.89, p = 0.199). There was no significant difference in HSI between the feeding regimes (F = 0.057, p = 0.826).
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Survival and health
Mortality peaked three times through the production cycle (Figure 11). In the first stocking, a total of 2935 of 10 547 (27.8%) fish died. The mortalities were suspected to be the result of enlarged livers (60%) and V. anguillarum infection (35%). Shortly after transfer, there was an outbreak of V. anguillarum, confirmed from bacteriology samples, and fish were treated with oxytetracycline (Aquinox, Novartis Animal Health). The fish were vaccinated ten months post-stocking in June, but this was too late to prevent a second episode of V. anguillarum. This was also treated with antibiotic, and the losses declined rapidly thereafter. The last peak in mortality occurred in spring 2004 and appeared to be associated with enlarged livers, in excess of 25% of body weight in most of the cases, compared with a site mean of 18.1 ± 2.3% for 50 fish sampled in March of the second year.
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Retarding maturation
None of the 150 haddock sampled from two tanks that were exposed to 24-h light at Gigha matured, whereas all 20 fish examined from one tank on the ambient light regime at Ardtoe had matured (Figure 12). The mean weights of the mature testes and ovaries from fish exposed to ambient light at Ardtoe were 10.3 and 63.7 g, for males and females, respectively, in contrast with only <1-g testes and 3-g ovaries for immature male and female fish exposed to 24-h light at Gigha. The GSIs were 1.4% and 8.6% for males and females, respectively, at Ardtoe, relative to less than 0.5% for immature females on a 24-h light photoperiod regime at Gigha.
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Performance in netpens
Haddock in netpens in Shetland were of 228-g mean weight in May 2004 and 217 ± 29 g in netpens in Northwest Scotland (Figure 13), which was not significantly heavier (t = 0.333, p = 0.741) than fish of a similar age in tanks (209 ± 39 g) at Gigha. SGRs were similar between netpens seven months post-stocking (Table 2) (in March, water temperature = 8°C), 0.83% in Shetland and 0.82% in Northwest Scotland, and the TGC was 1.53 and 1.48 in Shetland and Northwest Scotland, respectively. The FCR was 0.73 in Northwest Scotland in March 2004 compared with 0.75 in tanks at Gigha. However, by the second sea year (17 months after stocking), the mean weight of haddock in tanks at Gigha was slightly higher than in netpens in Northwest Scotland, although not significantly different (t = 1.39, p = 0.17). Mean weights of haddock in netpens in Shetland were lower from 14 to 17 months post-stocking compared with the other two locations.
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Quality assessment
Haddock were harvested in July 2004, and they compared favourably with wild fish from the North Sea (Table 3). Skinless and boneless fillet yield was 46% of whole body weight.
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Discussion |
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TopIntroductionMaterial and methodsResultsDiscussionReferences |
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Growth
Body weight, SGR, and FCR of haddock in this study were lower than for cod under similar conditions, with haddock attaining a mean weight of 755 g after 22 months compared with 3 kg for farmed cod. Before grading, haddock were maintained at a high stocking density in the smaller 5-m tanks (up to 47 kg m–3), and growth seemed to improve temporarily after transfer to the larger tanks in June (Figure 2). This can be compared with cod in experiments where SGR declined from low to high stocking densities of up to 40 kg m–3 (Lambert and Dutil, 2001). Poor growth performance could also be attributed to a sub-optimal diet containing lipid levels that were too high for haddock to utilize.
Although it would be expected that the growth of fish in tanks may be faster because of the reduced loss of feed through net meshes, and consequently lower FCR than in netpens, the growth of haddock at the two sea sites was similar to fish in tanks at Gigha for the first seven months. Current growth rates of cultured haddock are uncompetitive when compared with cod. This could be addressed through a selective breeding programme (C. Frantsi, pers. comm.), improvements in the diet, and a better understanding of the effects of feeding periodicity on growth.
Enlarged liver
The enlarged livers (HSI: 17–31%) indicate that haddock stored surplus lipids in the liver rather than muscle. These values are higher than the 12% HSI for cultivated cod (Shahidi and Dunajski, 1994). This is despite the fact that the liver has been identified as a main site of lipid storage in cod with a retention of up to 60% of absorbed dietary lipids (Dos Santos et al., 1993). In contrast, salmonids are capable of storing lipid in the muscle (Maeland, 2001). Liver weight has been reported as a major problem in haddock culture in Canada, with HSI exceeding 20% when lipid levels in the diet were >12%. The increase was mainly the result of total lipid in the diet, which affects fish health (Nanton et al., 2001). In their study, fish with high liver weights converted dietary energy into growth less efficiently. They recommended that haddock diets should contain around 14% lipid to minimize what was termed "fatty liver condition" in juvenile haddock (Lall et al., 2003). However, as demonstrated here, this value is still too high. The highest growth rate and best FCR were obtained using a diet with 11% lipid (Lall et al., 2003). It is difficult to produce extruded pellets with oil levels lower than 12% (H. Sveier, pers. comm.) as fishmeal is composed partly of oil, although additional oil must be added to bind the pellet. In this study, HSI was not related to fish weight but was significantly correlated to time on the diet. When the lipid in the diets was reduced from 14% to 12%, the HSI was stabilized initially for 12 weeks but was not maintained thereafter.
FCR and SGR in the present study, although lower and higher, respectively, when feeding fish every third compared with daily or alternate day feeding, were not significantly different from these treatments. In contrast, Lall et al. (2003) found that growth of juvenile haddock (c. 7 g) fed only once daily or on alternate days was significantly less than fish fed more frequently. The present trial was carried out with larger fish, around 70 g.
Health and vaccine development
The bacterial disease V. anguillarum is regarded as the main health threat to the farming of gadoids (Bricknell et al., 2006), and the 35% stock loss of haddock in tanks confirmed this. This may have been the result of the lack of vaccination at the hatchery and the ten-month delay in vaccination at the on-growing farm. A vaccination strategy of bath immersion at the hatchery and intra-peritoneal vaccination for fish at >30 g should be a priority. Although the fish were vaccinated in June with a Vibrio vaccine (AVL), the Vibrio vaccines in the UK are licensed for use with salmon and do not use the serotypes of Vibrio 2a and 2b normally detected in marine fish and, therefore, may be less effective.
Delaying maturation
Marine species will require higher light intensities to retard maturation relative to salmon (Davie, 2005). The three lights used in this study produced a high light intensity (50 lux), which is higher than the value of 1–2 lux recorded at the perimeter of salmon netpens (A. Davie, pers. comm.). Therefore, it is not surprising that, in the present study, none of 150 fish examined at an age of two years were maturing. These results support more detailed studies under an experimental setting (Davie, 2005), in which haddock were exposed to two light treatments, and maturation was delayed. Haddock broodstock held at the Ardtoe hatchery matured at an age of two years on an ambient light regime. However, unlike the experimental study by Davie (2005), the liver weight of maturing haddock in our Ardtoe tanks did not decline on maturation as the HSI (17.6%) was not significantly different from that of immature fish at Gigha (17.4).
Economics and future for haddock farming
In conclusion, rearing of haddock is technically feasible, but further improvements are required in hatchery techniques. For example, diets with reduced lipid and lower energy must be developed for on-growing. In the short term, the low price for wild haddock in the UK following the strong 1999 year class makes the economics of farming unattractive. However, rapid changes in stock abundance and vagaries in environmental conditions may not yield another strong North Sea haddock year class for many years. These factors may make haddock culture economically viable despite the poorer growth performance compared with cod. The industry should target farmed haddock as a substitute for premium, wild, line-caught fish of high quality, particularly off Iceland and particularly at times when wild fish are seasonally unavailable. While cod farming is an attractive proposition, further diversification of cold temperate aquaculture to other gadoids such as haddock should be considered.
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Acknowledgements |
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Support was provided by the partnership of the Sea Fish Industry Authority, Mainstream Scotland, Macrae, EWOS Innovation, Marks and Spencer Ltd, the Highlands and Islands Enterprise, Aberdeenshire Council, with backing from the British Marine Finfish Association. We are extremely grateful to the enthusiastic staff at Ardtoe Marine Laboratory, the Mainstream Isle of Gigha Pumpashore site, Johnson Seafarms, and Finfish Ltd for assistance with the hatchery phase and on-growing of haddock.
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References |
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