Black Tanks Research Articles

Combined effects of photoperiod and salinity on growth, survival, and osmoregulatory ability of larval southern flounder Paralichthys lethostigma

The southern flounder, Paralichthys lethostigma, is an important commercial and recreational marine flatfish that inhabits estuaries and shelf waters in the south Atlantic, from North Carolina through the Gulf coasts, with the exception of south Florida. Because juvenile and adult fish are highly euryhaline, it is a prime candidate for aquaculture. Methods for captive spawning of southern flounder are well developed; however, information on optimal culture requirements of the early larval stages is required for reliable mass production of juveniles. To determine the optimal photoperiod and salinity conditions for culture from hatching to day 15 post-hatching (d15ph), embryos were stocked into black 15-l tanks (75 l −1) under four photoperiods (24L:0D, 18L:6D, 12L:12D, and 6L:18D) and two salinities (25 and 34 ppt) in a 4×2 factorial design. Temperature was 18 °C, light intensity was 150 lx, and aeration was 50 ml min −1. Significant ( P<0.05) effects of photoperiod and salinity on growth (notochord length, wet and dry weights) were obtained. Growth increased with increasing photoperiod and salinity and was significantly greater at 24L and 18L than at 12L or 6L, and at 34 than at 25 ppt. On d11ph and d15ph, significant interactive effects between photoperiod and salinity on growth (wet and dry weights) were also evident. Growth of larvae reared at 25 ppt increased with increasing photoperiod to a maximum at 24L, while growth of larvae at 34 ppt reached a plateau at 18L. While there were no significant photoperiod effects on these parameters, larval survival, body water percentage, and larval osmolality on d15ph were significantly higher at 34 than at 25 ppt (41% vs. 16% survival; 322 vs. 288 mosM kg −1; and 84% vs. 76% water, respectively), suggesting stress and nonadaptation to 25 ppt, a salinity more nearly isoosmotic than full-strength seawater. Since larvae from both salinity treatments were neutrally or positively buoyant at 34 ppt, but negatively buoyant at 25 ppt, larvae reared at 25 ppt probably allocated energy to maintain vertical positioning, compromising growth and survival. The results demonstrate that growth and survival of early-stage southern flounder larvae are maximized under long photoperiods of 18–24L and in full-strength seawater. Longer photoperiods probably extend the time larvae have for feeding, while full-strength seawater salinity optimizes buoyancy and vertical positioning, conserving energy. The results show that early larval stage southern flounder larvae are not entirely euryhaline, which involves not only the ability to osmoregulate, but to conserve energy under reduced buoyancy. This is consistent with suboptimal vs. maximal growth of larvae reared at 25 and 34 ppt, respectively, under 18L (i.e., photoperiod×salinity interaction). This is also consistent with other reports that tolerance to lower salinities in these euryhaline flatfish increases post-metamorphosis when transition from a pelagic to benthic existence alleviates the need to counteract reduced buoyancy.

Background colour influence on the stress response in cultured red porgy Pagrus pagrus

Red porgy Pagrus pagrus were placed and maintained in white, grey and black background fibreglass tanks for 2 weeks. Additionally, fish kept in white and black background tanks were then subjected to crowding stress. After 2, 9, 16 and 23 days, blood samples were taken and plasma cortisol, alpha melanocyte stimulating hormone (α-MSH) and glucose values were analysed and compared with values from uncrowded fish from white or black tanks. Measurements of plasma cortisol and α-MSH in unstressed red porgy from white, grey and black tanks revealed no significant differences among the three groups. However, the results show that background colour markedly affects the in vitro interrenal sensitivity to both α-MSH and ACTH, as interrenal cells from black adapted fish had become virtually unresponsive to both secretagogues. Crowded fish on a black background showed a prominent increase in plasma cortisol after 2 days, which was followed by a recovery. In fish crowded on a white background however, the increase of cortisol was lower but was maintained through the entire experiment. Plasma α-MSH levels increased at 23 days as a consequence of crowding; this increase was also dependent on the background, being more prominent in fish placed in white background tanks. Thus, in the red porgy, a white background appears to modify the stress response, particularly in the long term.

Feed availability and its relationship to survival, growth, dominance and the agonistic behaviour of the southern rock lobster, Jasus edwardsii in captivity

The effect of feed availability (ration level and feeding frequency) on the culture performance of the juvenile (5–22 g) southern rock lobster Jasus edwardsii was examined to determine whether multiple daily feeding of a formulated feed would stimulate growth. Furthermore, the relationships between feed availability, agonistic behaviour, dominance, growth and survival were examined. A total of 252 lobsters (mean weight 5.26 g) were stocked into 28 black 52-l tanks at a density of nine lobsters per tank (42 m −2) and maintained at a temperature of 18.8 °C in a recirculating seawater system for 119 days. Lobsters were fed with high (4% BW day −1) or low (0.5% BW day −1) rations divided between one, two or four meals per day. These regimes were compared to a regime of fresh mussels ( Mytilus edulis) fed to excess once per day. Feeding lobsters with a high-ration level, 4 day −1, made no significant ( P>0.05) improvements in specific growth rate (SGR) (0.77–0.82% BW day −1), survival (75–84%) or biomass yields (96–102 g) compared to feeding 1 or 2 day −1. Low-ration-fed lobsters had a higher final mean weight (17.5–20.9 g) compared to high-ration lobsters (13.4–14.3 g), however, survival of lobsters that were fed with low ration of 4 day −1 (41%) was significantly ( P<0.05) lower than that of high-ration-fed lobsters (75–84%). The larger final mean weight of lobsters, fed with a low ration, was explained by the increased nutrient uptake from cannibalism. Significantly ( P<0.05) higher biomass yields were achieved by lobsters fed with fresh mussels once per day which was achieved through the combined effects of larger final mean weight (17.1 g) and improved survival (91%). Lobsters were size-ranked (g) to determine the effects of feed competition on the growth and survival of individuals of different rank. The ability and/or motivation of the largest lobsters to maintain their size status increased as feed availability decreased, suggesting that feed restrictions increased the strength of dominance. Size-ranking also demonstrated that small lobsters were more vulnerable to being cannibalised, especially when the feed-ration level was low. Feed competition was consistent with the concept of economic defensibility, predicting that levels of agonistic behaviour are highest when a low ration was patterned into smaller, more easily defended meals (low-ration fed, 4 day −1). In contrast, feed competition and agonistic behaviour were rarely observed when feed was freely available (high-ration fed, 4 day −1). The high levels of cannibalism of small size-ranked lobsters meant that assessing growth depensation was not a useful approach to the evaluation of the relationships between competition and growth in groups. The implications for J. edwardsii culture are that feeding high-ration levels of formulated feeds, more than once daily, reduces feed competition and incidence of agonistic behaviour. However, there appear to have few benefits in terms of growth or survival. The recommendation from this study is to feed lobsters once daily to excess after dusk.

Physiological and Behavioral Stress Responses of Walleyes Transported in Salt and Buffered-Salt Solutions

To evaluate the value of transporting fingerling walleyes Stizostedion vitreum in buffered sodium chloride, we monitored blood chemistry, behavior, and water quality in conjunction with two 5-h transport trips. The control salt mixture was 0.50% sodium chloride (NaCl), and the buffered treatment was 0.45% NaCl and 0.05% sodium bicarbonate (NaHCO3). We also collected posthaul blood samples from walleyes 2 h after they were placed into cages in East Okoboji Lake, as well as daily during a 72-h recovery period in hatchery raceways. Behavior was tested before and after hauls to quantify any disorientation that might occur as a result of hauling procedures. The addition of NaHCO3 to haulingtank water significantly increased the pH and alkalinity of the water compared with the unbuffered control. Overall, buffering produced significant effects on water chemistry but only minor effects on physiological measures of stress and the acid–base balance. In part, the effects of ram-air ventilation in removing excess CO2 and the fact that the water had moderate alkalinity levels to begin with negated the beneficial effects of buffering. Buffering is likely to confer benefits in situations where is alkalinity is low and there is poor ventilation of the hauling tank. Before and after hauls, we tested the preference of walleyes for a black or white tank background with a simulated predator (black brush). In both hauls, before the haul fish in all groups chose a black background more often than the white background. After hauling, fish in the control group sometimes showed preference for a white background, but fish in the buffered water never showed a preference for a white background. Many fish stocked directly into the lake remained near the lake bottom close to the boat ramp for at least 5 h after stocking. The most conspicuous changes in blood chemistry occurred in fish 2 h after they were stocked into floating cages. Our results suggest that fingerling walleyes are disoriented following a 5-h haul and would benefit from a recovery period prior to stocking.

Effect of dietary (n-3) highly unsaturated fatty acids on growth and survival of fat snook (Centropomus parallelus, Pisces: Centropomidae) larvae during first feeding

The effect of rotifers, Brachionus rotundiformis (S-type), fed three different diets: A (rotifer fed Nannochloropsis oculata), B (rotifer fed N. oculata and baker's yeast, 1:1), and C (rotifer fed N. oculata and baker's yeast, 1:1, and enriched with Selcoregister mark or target), was evaluated based on the survival, growth and swim bladder inflation rate of fat snook larvae. Rotifers of treatment A had higher levels (4.58 mg/g dry weight) of eicosapentaenoic acid (EPA) than B (1.81 mg/g dry weight), and similar levels (0.04 and 0.06 mg/g dry weight, respectively) of docosahexaenoic acid (DHA). Rotifers of treatment C had the highest levels of EPA (13.2 mg/g dry weight) and DHA (6.08 mg/g dry weight). Fat snook eggs were obtained by spawning induction with human chorionic gonadotropin. Thirty hours after hatching, 30 larvae/liter were stocked in black cylindric-conical tanks (36-liter capacity). After 14 days of culture, there were no significant differences among treatments. Mean standard length was 3.13 mm for treatment A, 3.17 mm for B, and 3.39 mm for C. Mean survival rates were very low (2.7% for treatment A, 2.3% for B, and 1.8% for C). Swim bladder inflation rates were 34.7% for treatment A, 27.1% for B, and 11.9% for C. The lack of differences in growth and survival among treatments showed that the improvement of the dietary value of rotifer may not have been sufficient to solve the problem of larval rearing. Some other factor, probably pertaining to the quality of the larvae, may have negatively influenced survival.

Effects of Photoperiod and Substrate on Larval Development and Substrate Preference of Juvenile Southern Flounder, Paralichthys lethostigma

ABSTRACT During the last decade, decreased landings of flounder along the mid- and south Atlantic coast have stimulated interest in flatfish aquaculture. The euryhaline southern flounder, Paralichthys lethostigma, is tolerant of great salinity and temperature ranges, making it a good aquaculture candidate. A 54-day study was undertaken to investigate the effects of photoperiod and substrate type on survival and growth of larvae and on pigmentation of recently metamorphosed juveniles. Photoperiod treatments consisted of continuous light, which is the current practice in flatfish aquaculture; 10 hours of light, which mimics the natural photoperiod; and continual darkness, to examine effects on visual feeding. Substrate treatments consisted of either no sand (bare, black fiberglass tanks) or sand-covered tank bottoms. All fish in the continual darkness treatment died within 18 days of hatching. Photoperiod and substrate type significantly affected survival. Survival was higher in the 10 hours of light treatment than in the 24 hours of light treatment (24% vs. 12%, respectively) and in the no sand treatment compared to the sand treatment (13% vs. 4%, respectively). There was no difference in mean total length of metamorphosed juveniles. There were no treatment effects on the percent normally pigmented juveniles. A study examining substrate preference indicated that small juveniles preferred mud and sand substrates over black or white bare tank bottoms. It was also shown that juveniles can readily adapt to a dark substrate. However, adaptation to a tan-colored sand background required a long time period, and some fish were not able to adapt, even after 19 days of exposure.

Effects of background color on growth performances and physiological responses of scaled carp ( Cyprinus carpio L.) reared in a closed circulated system

Growth performances and physiological responses of Cyprinus carpio after long-term (14 weeks) background color adaptation were investigated. Six groups of ten individuals each (initial body weight 116 g) were reared in black, green and white tanks (two replicate groups for each color). At the end of the experiment, blood (cortisol, glucose, haematocrit, cholesterol, triglycerides, total lipids, osmolality, electrolytes, pCO 2, pH), liver (total lipids, glycogen, hepatosomatic index) and growth (body weight, specific growth rate, food conversion ratio, condition factor, proximate carcass composition) parameters were determined. Plasma cortisol levels in white-adapted carp were significantly ( P<0.05) lower than those in black, while in green-adapted fish did not differ significantly from those in both other counterparts. White-adapted carp showed the highest specific growth rate and the lowest food conversion ratio, whereas black-adapted fish exhibited the opposite pattern. In addition, mean (%) increase of body weight in white-adapted carp was 4.66 and 3.58% higher than that in black- and green-adapted fish, respectively. Furthermore in white-adapted carp, blood pCO 2 and pH were significantly higher and lower, respectively, than those obtained in black- and green-adapted fish. In black-adapted carp, liver total lipid levels were significantly lower, and plasma total lipid levels were significantly higher, than those in white- and green-adapted fish. No significant variations were observed in the other parameters. It is concluded that different background colors may lead to different growth performances of scaled carp depending upon rearing conditions.

The effect of photoperiod, tank colour and light intensity on growth of larval haddock

In two separate experiments, haddock (Melanogrammus aeglefinus) larvae were raised under different photoperiods (24L : 0D or 15L : 9D), or different combinations of tank colour (black or white) and light intensity (1.1 μmol s−1 m−2 or 18 μmol s−1 m−2). Growth (0.8% day−1 in standard length; 2.9% day−1 in body area) and survival (2%) were not significantly different between photoperiod treatments after 35 days. Larval survival was greater in white versus black tanks after 41 days (2% versus l%, respectively). Growth of larvae was impaired in black tanks at low (1.1 μmol s−1 m−2) light intensity (0.8% day−1 in standard length and 2.2% day−1 in body area versus 1.1% day 21 in standard length and 3.1% day−1 in body area, for all other treatments). Transmission and reflection of light was low in black tanks at low incident light, and there was very little upwelling light. The resultant poor prey to background contrast probably resulted in larvae being unable to consume sufficient food to sustain a level of growth comparable to that in other treatments.

'This Machine Is Obsolete'

'This Machine Is Obsolete'

Response of phytoplankton communities to nitrogen input reduction in mesocosm experiments

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 179:187-199 (1999) - doi:10.3354/meps179187 Response of phytoplankton communities to nitrogen input reduction in mesocosm experiments V. Escaravage1,*, T. C. Prins1, C. Nijdam1, A. C. Smaal2, J. C. H. Peeters2 1Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, PO Box 140, 4400 AC Yerseke, The Netherlands 2National Institute for Coastal and Marine Management/RIKZ, PO Box 8039, 4330 EA Middelburg, The Netherlands *Address for correspondence: National Institute for Coastal and Marine Management/RIKZ, PO Box 8039, 4330 EA Middelburg, The Netherlands. E-mail: v.escaravage@rikz.rws.minvenw.nl ABSTRACT: The effects of a reduction in inorganic nitrogen input on phytoplankton communities (species composition, biomass and production) were studied in mesocosms. Experiments were conducted in 6 land-based mesocosms consisting of 3 m3 black polyethylene tanks. Light climate, temperature, mixing regime, and P and Si input were regulated to reproduce conditions comparable to those in Dutch coastal waters. Three levels of nitrogen availability were applied to the mesocosms used as replicates in 2 experiments, of 4 wk, in May-June and June-July 1994. In Expt 1, after 10 d in all treatments, diatoms (mainly Nitzschia delicatissima) became Si-limited and flagellates dominated phytoplankton. Within the group of flagellates, Phaeocystis sp. dominated numerically in the last week of the experiment when N was limiting and irradiance had increased. Phaeocystis sp. concentrations were higher in the mesocosms with the highest nitrogen load. In Expt 2, after the collapse of the initial diatom bloom due to Si-limitation (Thalassiosira sp.), an N-limited Phaeocystis sp. bloom developed and dominated the flagellate community. The decline of the Phaeocystis sp. bloom occurred together with the development of a second diatom bloom (Leptocylindrus danicus) under N-limitation. Phytoplankton biomass and production in these experiments reached levels measured in MERL mesocosm experiment for similar N-additions. The response of primary production to N-additions was tuned by the availability of light and other macronutrients. A saturation model could be fitted to observations with a set of parameters corresponding to representative ecophysiological characteristics. Phytoplankton species composition was related to season and resembled field communities observed in similar periods of the year. N-limited Phaeocystis colonial blooms were observed in mesocosms where 50% of the N-pool consisted of NH4+. KEY WORDS: Nitrogen · Mesocosm · Primary production · Nutrient limitation · Competition · Diatoms · Phaeocystis sp. Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 179. Publication date: April 15, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Effects of light intensity, tank colour and photoperiod on swimbladder inflation success in larval striped bass, Morone saxatilis (Walbaum)

Striped bass, Morone saxatilis (Walbaum), larvae, although physoclistous as adults, initially need to inflate their swimbladders by passing ingested air through a pneumatic duct to the swimbladder. Failure to inflate the swimbladder results in swimbladder atrophy, dysfunctional buoyancy control, deformities, and poor larval survival and growth. The present investigation studied the effects of light intensity, tank colour and photoperiod on the initial swimbladder inflation success of striped bass. In the first experiment, newly hatched larvae were reared for 2 weeks in black or white 350-L circular tanks exposed to incandescent lighting at 163 or 10 lux. Larvae were fed Artemia from 6 days post-hatching (dph). The standard length, and oil globule and yolk areas were measured. Swimbladder condition and evidence of feeding were recorded. To study the effects of photoperiod on inflation, larvae were reared in black tanks exposed to either 8 h:16 h or 16 h:8 h light:dark photoperiods at 139 lux. Striped bass inflated their swimbladders between 6 and 9 dph at 17 oC. Inflation success was significantly higher in black tanks (65%) compared with white tanks (42%), but light intensity did not significantly affect swimbladder inflation. Larval growth and food consumption were better in black tanks, primarily because this treatment resulted in more larvae with inflated swimbladders, although larvae with uninflated swimbladders in black tanks were longer at 12 dph than larvae with inflated swimbladders in white tanks. Larvae that successfully inflated their swimbladders fed earlier and exhibited better growth than larvae with noninflated swimbladders. Larvae reared at higher light intensities used up yolk reserves faster. Exposing striped bass larvae to 8 h:16 h light:dark photoperiods resulted in higher inflation rates (55%) compared to larvae reared at 16 h:8 h light:dark photoperiods (30%). Therefore, black tanks and short photoperiods are preferable for early rearing of striped bass larvae to maximize swimbladder inflation success.

トラフグ稚魚の成長と尾鰭の形状に及ぼす飼育水槽の色，照度および飼育密度の影響

In order to optimumize rearing conditions for seed production of the tiger puffer Takifugu rubripus, the influence of tank color, light intensity, and rearing density on the growth and the normality of caudal fin was examined. Juveniles (36.0mm in total length) were reared under six different conditions for 20 days. Total length, body length, body weight, and the normality of caudal fin reared in a black tank, at low light intensity (1, 000Lx), or at low rearing density (300 individuals per m3) were higher than those of the fish reared in white tank, at high light intensity (4, 000Lx), or at high rearing density (600 individuals per m3), respectively. In addition, the best result was obtained when fish were reared under combined rearing conditions in a black tank, at low light intensity, and at low rearing density.

Communications: Tank Culture of Larval Sunshine Bass

Abstract In 1995, two studies were conducted at the Marine Resources Research Institute, Charleston, South Carolina, that focused on development of techniques to intensively rear larval sunshine bass, the hybrid of female white bass Morone chrysops and male striped bass M. saxatilis. During the first study, the rotifer Brachionus plicatilis was shown to be an acceptable first-food when fed at 10 organisms/mL in static black tanks receiving high surface illumination (mean, 600 lx). It was further demonstrated that larvae could be switched to a diet of just nauplii of Artemia sp. by at least day 8 post-hatch. At the conclusion of the 8-d study, larvae fed Artemia nauplii earlier were significantly larger (9.12 mm total length, TL) than larvae fed rotifers through day 7 posthatch (6.71 mm TL). However, there were no survival differences (mean, 67.2%). During the second study, supplementation of the Artemia nauplii diet with a commercial larval feed offered no advantage to 12-d-old larvae, which had similar survival rates (mean, 92.0%) and sizes (15.3 mm TL) at the end of the 9-d study. However, it was not clear whether the larvae ate the commercial larval feed. At the conclusion of the controlled larval rearing studies, the small juveniles were placed in industry scale tanks (1.9 m diameter × 0.8 m deep) and converted to a dry diet by day 32 posthatch. By age 46 d, 62.2% of the juveniles had survived the transition to a dry diet, and average size was 59.7 mm TL (average weight, 2.9 g). Combining results, cumulative survival from age 3–46 d was approximately 38%, which is comparable to that of extensive pond culture systems. The intensive tank culture techniques, when coupled with controlled spawning of domesticated broodstocks, should allow year-round production of juveniles for use in the expanding hybrid striped bass aquaculture industry.

The effect of background color and rotifer density on rotifer intake, growth and survival of the grouper ( Epinephelus suillus) larvae

Rotifer intake and early growth and survival of Epinephelus suillus larvae were determined in terms of rotifer visibility against the background color of rearing tanks and density. The larvae were stocked at 30 l −1 in 200-l fiberglass tanks with phytoplankton (green water). Larvae were fed rotifers at densities of 5, 10 and 20 ml −1. Growth and survival were comparable among larvae in both tan and black tanks with green water. Rotifer intake was significantly higher in larvae in tan tanks. In black tanks, the survival of larvae at Day 14 was enhanced by the high rotifer density of 20 ml −1. Rotifer intake and growth of larvae were similar at all densities.

The Morris Water-Escape Task in Mice: Strain Differences and Effects of Intra-Maze Contrast and Brightness

The Morris water-escape task is an extensively used experimental paradigm to assess the spatial discrimination performance and effects of brain lesions and drugs on this performance. In the first experiment, we compared the acquisition of this task by different strains (CFW1, BALB, NMRI, and C57BL) of mice and their performance in a probe trial. In a second experiment, C57BL mice were tested in Morris mazes where black and white tanks were combined with white or black platforms to investigate if and how the contrast between the tank and the platform affects the performance of the mice. In addition, four brightness conditions were compared to investigate whether or not the degree of brightness of the tank itself affects the learning performance. The results of these experiments indicated that 1. mice could readily learn the Morris task, 2. one of the contrast conditions affected the swimming speed, 3. the maze brightness per se did not affect water escape performance at all, and that 4. the swimming speed can strongly bias the outcome of Morris water-escape experiments in mice.

Morpho-physiological Responses of Pinus halepensis Mill. Seedlings to Drought Stress

Aleppo Pine (Pinus halepensis Mill.) is known to be the most drought-resistant Mediterranean Pine. This species is widely distributed throughout the Mediterranean region and displays a high intraspecific variability, with respect to its physiological and morphological response to environmental conditions. In this experiment we evaluated the response of Pinus halepensis seedlings to drought. Sixty germinated seeds (accession A6, Shaharia, Israel) were grown in soil for 8 weeks and then transferred to black plexiglass tanks containing half-strength air-sparged Hoagland solution. After 6 weeks of acclimation to hydroponics, the osmotic potential of the solution was lowered by adding polyethylene-glycol (PEG) 8000. Water potential was lowered in 0.2 MPa increments every 4 days, until a final value of –0.8 was reached. The seedlings were then maintained at –0.8 MPa for a further 8 days. Ultrasonic acoustic emissions, pressure–volume (P–V) curves, shoot and root growth, leaf area, xylem diameter, root apex mitotic index and cell length were measured on control and stressed seedlings. Seedlings were then transferred to normal Hoagland solution for 24 hours to simulate rewatering, and P–V curves and ultrasonic emissions measurements were repeated. Results showed that the final root growth is maintained in the stressed seedlings at the same rate as controls, whereas shoot growth was significantly reduced. The leaf area was reduced by stress to 36%, but the xylem diameter only to 10%, leading to a lower leaf area:xylem section ratio in the stressed plants. Ultrasonic emissions in the stressed plants were 365% of the control, and 182%, after rewatering. Specific details of the growth and physiology data are presented.

Illumination in first feeding tanks for marine fish larvae

Illumination levels were measured in three artificially illuminated tanks (a black tank, a white tank and a tank with black sides and white bottom) in order to test how well normal tank illumination in different tank types corresponds to natural illumination conditions for first feeding of marine fish larvae. Measurements were made with clear water and with algae added (‘green water’). The black tank had low wall and bottom illumination. The white tank had high wall and bottom illumination. The black-walled white-bottomed tank had low wall and high central and bottom illumination. Green water attenuated light substantially. The black tank seemed best suited to reproduce natural illumination conditions. The white tank was not suited. The black-walled white-bottomed tank had interesting properties, but species specific tests would have to be carried out to fine tune the reflective properties of the bottom. Green water seemed to be beneficial in all tests.

The response of phytoplankton communities to phosphorus input reduction in mesocosm experiments

This study examines the effects of a reduction in the phosphorus input (in comparison to field levels) on natural coastal phytoplankton communities. Experiments were conducted in four land-based mesocosms consisting of 3 m 3 black polyethylene tanks. Light climate and mixing regime reproduced conditions in Dutch coastal waters, temperature was maintained within 2 °C of the ambient seawater temperature. Phytoplankton species succession and primary production were studied in two mesocosm experiments of 5 and 4 weeks in April and July 1993. In both experiments, inorganic nutrients were continuously added to four mesocosms. N (nitrogen) and Si (silicon) inputs were identical for the four mesocosms and resembled the inputs to the Dutch coastal zone. The phosphorus (P) input established a N P ratio gradient among the mesocosms: 16, 32, 64 and 128. The first experiment was carried out during the spring diatom bloom. The initial diatom dominance was maintained in the mesocosms with reduced phosphorus loads. In the mesocosm with the highest P input, flagellates developed to the detriment of the diatoms at the end of the experiment in parallel with the establishment of a silicate limitation. The second experiment coincided with the spring/summer phytoplankton bloom dominated by the colony of Phaeocystis sp. Diatoms outcompeted Phaeocystis sp. in the mesocosms with reduced phosphorus inputs ( N P = 32, 64, 128 ). In both experiments, maximum primary production rates were observed in the mesocosm with the highest P input and decreased with the phosphorus gradient. It was concluded that a reduction of the phosphorus loads to eutrophicated coastal waters determined a proportional reduction of the primary production and stimulated the dominance of diatoms over flagellates.

Validation of a Test Method for the Measurement of Methanol Emissions from Stationary Sources

Title III of the 1990 Clean Air Act Amendments designated methanol as a pollutant to be regulated. The U.S. Environmental Protection Agency (EPA), through a contract with Research Triangle Institute, has developed a method for measuring methanol emissions from stationary sources. The methanol sampling train (MST) consists of a glass-lined heated probe, two condensate knockout traps, and three sorbent cartridges packed with Anasorb 747. Samples are desorbed with a 1:1 mixture of carbon disulfide (CS2) and N,N-dimethylformamide (DMF). Condensate water and CS2/ DMF samples are analyzed by gas chromatography with flame ionization detection. The MST has a practical quantitation limit of approximately 3 ppm for a 20-L sample. Samples were shown to be stable for at least two weeks after collection. Field tests of the MST and the National Council of the Paper Industry for Air and Stream Improvement (NCASI) methanol sampling method were conducted at two pulp and paper mills. Sampling and analysis procedures followed EPA Method 301 requirements. The sampling location for the first field test was the inlet vent to a softwood bleach plant scrubber, where the methanol concentration was approximately 30 ppm. The mean recovery of spike was 108.3% for the MST method and 81.6% for the NCASI method. Although neither method showed significant bias at the 95% confidence level, the between-methods bias was significantly different. A second field test was conducted at a vent from a black liquor oxidation tank where the methanol concentration was approximately 350 ppm. Mean spike recoveries were 96.6 and 94.2% for the MST and NCASI methods, respectively. The biases of the two methods and the between-methods bias were not significantly different for the second field test.

An experimental system for small-scale experiments with marine fish and crustaceans

A small-scale experimental larval rearing unit was designed for controlled experiments on marine fish and crustacean larvae. The system uses 3 litre hemispherical, black tanks in sets of three with their own biofilter. Alternatively the whole system can be integrated to allow the use of 18 tanks. The system has successfully been used for work on the greenback flounder ( Rhombosolea tapirina). The main problems have been preventing the formation of surface oil films when using live feeds and solid removal at weaning. However the aims of compactness, low cost and versatility were successfully achieved.