Growout of hatchery-reared juvenile spotted babylon (<Emphasis Type="Italic">Babylonia areolate</Emphasis> link 1807) to marketable size at four stocking densities in flow-through and recirculating seawater systems

Hatchery reared juvenile spotted babylon, Babylonia areolata, were raised in canvas rearing tanks at four stocking densities (100, 200, 300 and 400 ind. m^–2) in flow-through and recirculating seawater systems until they reached the marketable sizes of 100–140 snails/kg. At all stocking densities, final increments in mean length and weight of snails held in flow-through systems were higher than those in recirculating systems, there was a significant effect (p < 0.05) of culture system on final length and weight. Mean (±SE) survival of snails held at 100 ind. m^–2 in the flow-through system was 100.0 ± 0.1% but was not significantly higher than survival in any other treatment (p > 0.05). Mean survival of snails held in the recirculating system was not significantly lower than at any stocking density in the flow-through system (p > 0.05).     

Whole animal transepithelial potential (TEP) of coho salmon during the parr-smolt transformation and effects of thyroxine,prolactin and hypophysectomy

Whole animal transepithelial potentials (TEP) of yearling coho salmon (Oncorhynchus kisutch) in fresh water and after transfer to seawater were recorded throughout parr-smolt transformation (smoltification) from February to August 1984, along with plasma Na⁺ and Cl^– concentrations and osmolality. Based on plasma ion regulation in seawater, the yearling coho in this study completed smoltification and attained sea-water adaptability in April. TEP in freshwater fish decreased (became inside-negative) after smoltification, and the TEP increased significantly (P < 0.01) after seawater transfer. When fish were transferred into seawater, thyroxine increased TEP of the transferred smolts by approximately 30% over the control level (P < 0.01) in April, but this did not occur when freshwater postsmolts were transferred in July and August. Hypophysectomy increased TEP (P < 0.01) in fresh water; it did not affect the TEP of the fish after seawater transfer. Ovine prolactin (3 g/g body weight) implanted into seawater-adapted fish caused a reduction in TEP (P < 0.01) when fish were exposed to fresh water. Whole-animal TEP appears to provide a valuable index of the completion of smoltification (April–May) and a useful tool for investigating the endocrine control of salmonid osmoregulation.     

Evaluation of brook trout production in a coldwater recycle aquaculture system

Brook trout (Salvelinus fontinalis) are a commercially important coldwater species reared in Wisconsin and the Midwestern United States. Brook trout are raised by private, tribal, state, and federal fish hatchery facilities in Wisconsin. Approximately 10% of private coldwater aquaculture operations are presently raising brook trout of various strains for stocking uses and a limited amount for food markets. Growing brook trout to a larger size, if they can be reared in a shorter time span, may present a potential new sector for the aquaculture market in the Midwestern US. The present study reports hatchery production attributes, i.e., growth, survival, fin condition, feed efficiency, water chemistry requirements and general husbandry of Lake Superior strain (Nipigon) brook trout reared in a recirculating aquaculture system (RAS), operated at an average temperature of 13 °C. The recycle system at NADF reared 1379 kg of brook trout over a 10-month period from fingerling (9 g) to market size (340–454 g). The trout grew faster (0.84 g/day and 0.64 mm/day) in the RAS than fish cultured in traditional flow-through tank culture utilizing ground water at 7.6 °C (0.14 g/day and 0.35 mm/day). Final average weight of RAS fish was 260 g, while the flow-through fish averaged 65 g. Final tank densities for the RAS averaged 40.4 kg/m³ while flow-through tanks averaged 31.2 kg/m³. Throughout the project, feed conversions in the RAS ranged from 0.9 to 1.3. Water quality variables such as TAN, nitrite, DO, temperature, TSS, CO₂, ph, etc. were within safe limits for brook trout and will be discussed. It does appear from this initial research project that market size brook trout can be raised successfully in a recycle system within a similar time frame as a rainbow trout produced in a Wisconsin typical flow-through facility.     

Impact of smolt production strategy on vertebral growth and mineralisation during smoltification and the early seawater phase in Atlantic salmon (Salmo salar, L.)

This study investigates the effect of different smolt production strategies on vertebral morphology (radiology), composition (mineral content) and mechanical strength (load-deformation testing) in Atlantic salmon (Salmo salar). Rapid-growing underyearling (0+) smolt were compared with slower-growing yearling (1+) smolt and a reference group of wild smolt (w). The underyearling and yearling smolt were transferred to seawater in October 2002 and May 2003, respectively. The underyearling smolt were reared under continuous light and the yearling smolt under natural light during the first twelve weeks in seawater, at ambient temperatures. Thus, the underyearling smolt hit seawater at 13 °C and were reared at 10-13 °C during the early seawater phase, whereas the yearling smolt hit seawater at 7 °C and were reared at 7-10 °C during the early seawater phase. All groups displayed increased longitudinal growth (up to 9% increase in relative length) of the caudal vertebrae during parr-smolt transformation. However, at transfer to seawater, the underyearling smolt had significantly lower vertebral mineral content (0+ 44%, 1+ 47%, w 50%) and higher incidence of deformed vertebrae (0+ 1.5%, 1+ 0%, w 0%), and at twelve weeks after transfer to seawater significantly lower vertebral mineral content (0+ 36%, 1+ 41%, w 43%), yield-load (0+ 6492 g, 1+ 8797 g, w 9150 g) and stiffness (0+ 7578 g/mm, 1+ 15,161 g/mm, w 20,523 g/mm), and significantly higher incidence of deformed vertebrae (0+ 2.5%, 1+ 0.3%, w 0%). There was a significant correlation between the mineral content and mechanical properties of the vertebrae. The underyearling smolt had significantly elevated plasma concentrations of total Ca, and P and Ca²⁺ during the parr-smolt transformation and in the early seawater phase.The results show that underyearling smolt may have an increased risk of developing vertebral deformities. It is possible that this risk can be reduced by postponing the start of the short-day treatment. This will reduce the temperature during smoltification, the temperature and daylength during the early seawater phase, and increase the age at smoltification.     

Plasma insulin-like growth factor-I concentrations in yearling chinook salmon (Oncorhynchus tshawytscha) migrating from the Snake River Basin, USA

During the parr-to-smolt transformation (smoltification) of juvenile salmonids, preadaptive changes in osmoregulatory and ionoregulatory ability are regulated in part by the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis. If food intake is sufficient, plasma IGF-I increases during smoltification. On the other hand, plasma IGF-I typically decreases in fasting fish and other vertebrate animals. Because food availability is limited for juvenile salmonids undertaking an extended 6- to 12-week springmigration to and through the Snake-Columbia River hydropower system (northwestern USA), IGF-I concentrations might be expected to decrease, potentially compromising seawater tolerance. To address this possibility,yearling chinook salmon Oncorhynchus tshawytscha reared in three Snake River Basin hatcheries were sampled before release and at two downstream dams. Dry masses ofmigrating fish either did not increase during themigration (in 2000, an average-flow year), or decreased significantly (in 2001, a low-flow year). In both years, plasma IGF-I levels were significantly higher (1.6-fold in 2000, 3.7-fold in 2001) for fish sampled at the last dam on the lower Columbia River than for fish sampled prior to release. Plasma IGF-I concentrations inmigrating fish may, nonetheless, have been nutritionally down-regulated to some degree, because plasma IGF-I concentrations in juvenile chinook salmon captured at a Snake River dam and transported to the laboratory increased in fed groups, but decreased in unfed groups. The ability ofmigrating smolts to maintain relatively elevated IGF-I levels despiteRestricted food intake and loss of body mass is likely related to smoltification-associated changes in hormonal balance.     

Preparation of hatchery—reared chum fry for life at sea: osmoregulation dynamics

The development of saltwater tolerance was studied in chum fry reared in the Malkinsky hatchery (central Kamchatka, 200 km from the Sea of Okhotsk). Hypo-osmoregulatory ability of fry was assessed by dynamics of plasma sodium concentration, 24 and 48 h after their transfer from fresh water to seawater (30%o), and by fry survival in seawater of 40%o salinity. Complete osmoregulation function in young chum was developed in seawater only in late June, despite their earlier development of silver body color and fairly high migration activity. No correlation was found between the weight of fish and their osmoregulatory abilities. The reasons for late smoltification of hatchery-reared chum have not yet been clearly defined. One explanation might be the combined effect of low nocturnal temperatures and considerable daily fluctuations in temperature (more than 8^oC) during the period of egg incubation (in fall), as well as during smoltification of chum juveniles (spring-early summer). Data on the osmoregulatory ability of chum smolts could be useful in forecasting their survival in the early marine period of life.     

Rainbow trout (Oncorhynchus mykiss,Walbaum ) develop a more robust body shape under organic rearing

Prolonged exposure to captive conditions has led to the development of a rainbow trout ‘farmed’ phenotype, which is different from that of wild trout. Selection for desirable productive traits in hatcheries has resulted in the development of some morphological traits that are maladaptive in nature. The recent development of organic aquaculture, guided by the well‐being of the fish, could potentially produce a new farmed phenotype that would be more adaptive in nature. In this study, rainbow trout reared in intensive and organic farms were compared by means of shape analysis, to detect patterns of shape variation associated with rearing environment. The results of this study highlight a significant effect of the rearing method on rainbow trout shape: organically reared trout showed a higher body profile, in particular in the head and trunk regions, shorter median fins and a deeper caudal peduncle. A combined effect of density and habitat complexity could have contributed to the observed shape differences: in organic rearing systems, lower densities and steady water could increase territoriality and aggressive interactions, promoting body designs more functional in rapid attacks and escapes.     

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.     

Review of morphological and behavioural differences between reared and wild individuals: Implications for sea-ranching of Atlantic salmon, Salmo salar L., Atlantic cod, Gadus morhua L., and European lobster, Homarus gammarus L.

Abstract The main question which must be raised when planning to enhance natural populations through sea ranching is whether reared organisms are fit for a life in the wild, or more specifically, whether there are differences between reared and naturally resident individuals. The causes and effects of these differences are reviewed, and results from the Norwegian enhancement programme, which compared reared and wild individuals of Atlantic salmon, Salmo salar L., Atlantic cod, Gadus morhua L., and European lobster, Homarus gammarus L., are discussed with emphasis on morphological and behavioural differences. It was concluded that exposure to an artificial rearing environment during ontogeny can affect both the phenotype and the behaviour of the reared individuals, and thereby, their potential for survival after release into the wild as well. Suggestions are made as to how to diminish observed differences, and thereby, improve the survival potential.     

Seawater tolerance in Atlantic salmon, Salmo salar L., brown trout, Salmo trutta L., and S. salar?×?S. trutta hybrids smolt

High levels of hybridization between Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) have been reported in the Gyrodactylus salaris infected Rivers Vefsna and Driva in Norway. The survival and behaviour during the sea phase of such hybrids is unknown. The reported work documents ionoregulatory status after 24 h seawater challenge tests (24hSW) and gill Na⁺/K⁺-ATPase (NKA) activity of migrating wild smolts of Atlantic salmon, brown trout and hybrids at two sampling dates during the 2006 smolt run in River Driva. Salmon, trout and hybrids contributed to 27, 52 and 21% of the catches, respectively. The large contribution of hybrids suggests both a high hybridization rate and a high survival rate from fry to smolt. Both salmon and hybrids had a well-developed seawater tolerance at the time of downstream migration, revealed by small ionoregulatory effects and no or low mortality rates during the 24hSW tests. The trout were not fully adapted to seawater, and high mortality rates were observed (71 and 92%) during the 24hSW tests. The NKA activity was not significantly different between salmon and hybrids. Most of the hybrids were physiologically capable of direct entry to full strength seawater. The incomplete seawater tolerance in trout compared to salmon corresponds well with differences in life-history patterns between these two species. The life history strategy of the hybrids during the sea phase is not known, and further investigations on the marine behaviour and survival is needed to evaluate the role of hybrids in the risk of spreading G. salaris to nearby river systems.     

Kemp's Ridley Sea Turtle Waste Characterization Study: Precursor to a Recirculating Holding System Design

The decreasing population of the endangered Kemp's ridley sea turtle ( Lepidochelys kempi ) has necessitated research into more cost effective captive nurseries. Captive nurseries are an attempt to increase the survival of the Kemp's ridley past the first year of life. Presently, Kemp's ridleys are reared in captivity at the Headstart rearing facility in Galveston, Texas. This facility consists of a labor intensive, flow-through system. Alternatively, recirculating systems permit development of inshore facilities with decreased labor and operating costs. This paper presents baseline excretion data necessary for designing filtration units required for water quality maintenance in recirculating holding systems. The total ammonia nitrogen excretion rate based on a 24 hour isolation period (fed) was fairly constant at 0.19 mg N/g-turtle-day, while the BOD₅ loading rate was highly variable, averaging nearly 0.50 mg O₂/g-turt1e-day. In addition, comparisons of filtered versus nonfiltered samples suggest that a suspended solids removal mechanism prior to the filtration unit would dramatically decrease BOD₅ and, thus, improve filter efficiency and increase its capacity.     

Culture du saumon de l'Atlantique Salmo salar en eau salée dans l'estuaire du St-Laurent,Québec (Canada) avec hivernage en eau douce

On most of the eastern coast of Canada, the seawater is too cold during the winter to keep the Atlantic salmon Salmo salar continually. The authors therefore reared salmon in the St Lawrence estuary during the summer of 1983 and during the winter transferred them to the aux Outardes river and subsequently to a fish rearing station. They were put back in seawater the following summer until the fall of 1984. In 1983, a group of salmon, used for comparison, was reared in freshwater only. Starting with a mean weight of 43 g, an average weight of 1·28 kg after 17·3 months and a mean instantaneous growth rate of 0·64 % day⁻¹ were reached. The fish in seawater showed a better growth, ratio of feed to flesh conversion and rate of survival than the fish in freshwater. Despite a low survival of 32 %, it is concluded that the rearing of Atlantic salmon in seawater involving a wintering in freshwater is technically and biologically feasible. The heavy mortalities and the low growth can be explained by the fact that the fish were underfed at the beginning of the experiment.     

Can UV-treated seawater cause cataract in juvenile cod (Gadus morhua L.)?

The results indicate that seawater recently disinfected with ultraviolet radiation (254 nm) can increase the frequency of cataract in juvenile cod. In a 5-month experiment where groups of cod were reared in a recirculating system at two stocking densities (54 and 300 fish/m³), the frequency of cataract increased after the fish were exposed to UV-treated water. The tank with the water intake closest to the UV lamps (3 m) was affected the most, 39% of the fish developed cataract compared to 5% in the tank located furthest away from the UV lamps (33 m). The results suggest that there was some lag time between turning the UV light on and off and when the frequency of cataract stabilized. For each stocking density, the frequency of cataract decreased exponentially with increased post UV-treatment time, i.e., the time it took the seawater to run from the UV light to the rearing tanks. The calculated half-life of the effect was about 1 min at both densities. The effect of the UV light must have been indirect since the UV lamps were placed inside an opaque steel box. It is hypothesized that ozone or other photoproducts formed by UV radiation may cause cataract in fish. For a given post UV-treatment time, the frequency of cataract was about twice as high at high compared to low density suggesting that perhaps density-dependent abrasion of the cornea may enhance the effect of ozone or other photoproduct on the lens. In three tanks with low stocking density (55 fish/m³) and clean seawater (flow-through tanks), the frequency of cataract was less than 1% although the incoming seawater was also disinfected with UV light. The high residence time in the flow-through tanks (471 min) compared to the recirculating tanks (37 min) may explain why the cod in them were unaffected by UV-treated water. The results imply that UV lights must be used with great caution in fish farming to avoid the development of cataract.     

Development of Nursery Systems for Black Sea Bass Centropristis striata

Black sea bass (Centropristis striata) are territorial fish and cannibalism is a concern when rearing juveniles in intensive systems. Three studies were conducted to provide information for development of suitable tank nursery systems for juvenile black sea bass (3.6–4.5 cm; 0.8–1.7 g). Studies were performed at the Marine Resources Research Institute, Charleston, SC, using 1.5‐m diameter × 0.8 m deep tanks connected to recirculating seawater systems. The studies examined growth and survival at different stocking densities, selection and utilization of habitats, and, effects of water velocity on positioning and movement of fish. In study 1, fish were stocked at biomass densities of 126.7, 253.3, and 506.7 Wm³ and reared for 56 days with no habitats. No difference in growth was detected although fish reared at the lower densities had significantly lower mortality (mean 7.9%) as compared to those at the highest density (28.0%). At the highest density, cannibalism appeared to be a substantial cause of mortality. In study 2, three habitat types were used, (1) two‐tier structure constructed from plastic grating with 15 mm square openings (volume = 0.015 m³); (2) PVC pipe bundle (volume = 0.004 m³); (3) rock aggregate (volume = 0.008 m³). Of the habitats, the most utilized habitat (62.9%) was the two‐tier layered structure that allowed movement in all directions. The next utilized type was the pipe bundle (25.6%) with the openings inhabited by the largest juveniles in each tank. Overall, a mean of 18.2% of the fish were observed using habitats. Study 3 examined water velocities ranging from 0.01 to 0.12 m/sec. Most fish became concentrated in the tank bottom area having a water velocity in the range of 0.040.09 m/sec. At these velocities there were few aggressive interactions. Smaller fish inhabited the areas outside this velocity range. At the higher velocities, the small fish swam vigorously to maintain their position in the water column. At the low velocities, sporadic incursions of larger fish occurred presumably to attempt to cannibalize or to defend territory. Results from these studies help to define characteristics of nursery systems for rearing juvenile black sea bass.     

Groundwater water treatment for iron and manganese reduction and fish rearing studies applied to the design of the Ruth Burnett Sport Fish Hatchery, Fairbanks, Alaska

Studies at the Fairbanks Experimental Fish Hatchery (FEFH) were conducted to investigate the operational characteristics of media filtration groundwater treatment for iron and manganese reduction, water reuse and recirculation technologies for fish rearing, and conditions of fish gill tissue during rearing. Results were used to aid in the design and planned operation of the Ruth Burnett Sport Fish Hatchery (RBSFH), currently under construction in Fairbanks, Alaska. Under a two-stage filtration scenario, with hydraulic loading rates of 0.39 and 0.43 cm/s for Stages 1 and 2, respectively, manganese dioxide media filtration typically removed dissolved iron from 5 to 6.5 mg/L down to 0.1 mg/L or less, and allowed for suitable fish rearing and health (based on gill condition) in treated groundwater. Poor water quality from filter equipment malfunction or improper operation typically manifested tissue damage (epithelial lifting, hypertrophy, degeneration, and in some cases iron adhesion) observed in fish gills. Design refinements from initial use, including changes in hydraulic loading rates and transition from single-stage to two-stage filtration, were required for long-term use of media filtration and were included in the design of the future hatchery. Dissolved manganese removal from groundwater (from 0.7 to <0.05 mg/L) was also implemented by continuous low-level potassium permanganate addition. Small-scale flow-through, fully recirculating, and partial reuse rearing systems were used to mimic planned future fish production, and resulted in 97% or greater survival and adequate growth (average specific growth rate between 1 and 2%) and health of rainbow trout during most rearing trials.     

Water temperature and dietary histidine affect cataract formation in Atlantic salmon (Salmo salar L.) diploid and triploid yearling smolt

The aim of the present study was to investigate cataract development in diploid (2N) and triploid (3N) Atlantic salmon smolts and post‐smolts at two water temperatures (10 and 16 °C) given diets with different histidine supplementation (LH, 10.4 and HH, 13.1 g kg^?1) before and after seawater transfer. In freshwater, a severe cataract outbreak was recorded in both ploidies reared at 16 °C. The cataract score was significantly higher in triploids compared to diploids, and the severity was lower in both ploidies fed the HH diet. The cataract development at 10 °C was minor. Low gill Na⁺, K⁺‐ATPase activity in fish reared at 16 °C before seawater transfer was followed by osmoregulatory stress with elevated plasma electrolyte concentrations and high mortality in sea water. Both diploids and triploids reared at 10 °C developed cataracts during the seawater period, with higher severities in triploids than diploids and a reduced severity in the fish fed the HH diet. The findings of this study demonstrate the importance of environmental conditions in the husbandry of Atlantic salmon, and particularly triploids, with regard to smoltification and adjusted diets to mitigate cataract development in fresh and sea water.     

Intensive culture of lake whitefish (Coregonus clupeaformis Mitchill) using Artemia and artificial feed

Whitefish larvae were reared using combinations of live Artemia nauplii and trout starter. In all cases survival was greater than 93% at 9 weeks of age. Growth did not differ significantly (P>0.1) between high and low feeding rates of live nauplii; however, an opercular cover malformation was detected at the lower rate. A conversion program was developed for the practical use of Artemia nauplii. Whitefish were successfully converted to trout starter at 7 weeks of age and 140 mg. Trout starter alone was inadequate for early rearing. Decapsulated, lyophylized cysts of Artemia were almost a replacement for live Artemia nauplii except for a low incidence of opercular cover malformation. Advanced rearing to yearling size was easily performed with trout feed. Additional mortalities were less than 3% to 14 months of age at stocking.     

Survival and distribution of pond- and hatchery-reared 0+ brown trout, Salmo trutta L., released in a Swedish stream

During 1985-88, a total of 17500 under-yearling (0+) brown trout. salmo trutta L., were released in Låktabäcken Creek in Swedish Lapland. Of these, 15500 had been reared in a pond adjacent to the creek during their first summer, where they fed on natural prey. The other 2000 were conventionally reared hatchery fish fed dry food pellets. All fish were released in the autumn (size 6O-70mm) at the confluence of the pond outlet and the creek. Electrofishing revealed that the stocked fish gradually spread downstream from the point of release at the expense of the resident wild trout population. In 1989, stocked fish accounted for 70-90% and 30-50% of the trout population in the upper and lower stretches of the creek respectively. No long-term changes in total trout densities or standing crop occurred as a result of stocking. First-year survival of fish released in the creek varied between 15 and 30% over the 4 years. After 3 years, 5% of the stocked fish remained in the creek. Planted fish grew less rapidly than wild fish during the first year in the creek. Pond fish had a higher survival rate than hatchery fish and showed a greater propensity to disperse from the point of release.     

Growth and parr-smolt transformation of Atlantic salmon (Salmo salar L.) under different light intensities and subsequent survival and growth in seawater

Groups of potential Atlantic salmon (Salmo salar L.) smolts were reared under a simulated natural photoperiod from November 1987 to May 1988. Three different light intensities were used: 27, 335 or 715 lux. Growth rate was not significantly influenced by differences in light intensity. All groups developed the silvery external appearance, increased hypo-osmoregulatory ability and decreased condition coefficient associated with smolting. Smolts from all groups were successfully acclimatized to seawater in early May. The subsequent seven months of rearing in seawater did not reveal any differences in post-smolt performance of the groups. The incidence of early maturation during the first autumn was similar in all groups. We conclude that within the limits of the light sources used in the present experiment, light intensity had no significant effect on the growth and smolting in juvenile Atlantic salmon.     

Mortality of marine cultured rainbow trout, Oncorhynchus my kiss (Walbaum), during the summer in the Netherlands

Abstract. In northern Europe, rearing of rainbow trout, Oncorhynchus mykiss (Walbaum), in sea cages is a substantial part of fish culture. One of the major constraints for the development of this system in other parts of Europe is the unexplained mortality of fish during the summer. To investigate environmental aspects of this mortality, rainbow trout, cultured in cages in sea water, were monitored from May to October for three successive years. No evidence of bacterial involvement could be found, while water temperature and salinity strongly influence the mortality. This supports the suggestion that the mortality has been caused by patho-physiological changes due to higher metabolic requirements for osmoregulation at elevated water temperature in the saline environment which might result in a dissipation of O₂ by CO₂ on the hemoglobin.