Replicate Aquaria Research Articles

Optimizing nursery diets for post‐metamorphic stage black sea bass: Growth performance, body composition, and feed utilization on open‐formulated and commercial starter diets

AbstractThe objective of this study was to optimize nursery diets for post‐metamorphic stage black sea bass by evaluating growth performance, whole‐body proximate and fatty acid composition, and utilization of University of North Carolina Wilmington (UNCW)‐formulated and commercial diets under laboratory conditions. A feeding trial was conducted to compare two UNCW‐formulated diets (D1 and D2) for black sea bass (54% crude protein = CP and 14% crude lipid = CL) and two premium, commercial marine finfish fry diets, Otohime (Reed Mariculture Inc., Campbell, CA, CP = 48% and CL = 14%, CD3) and Gemma Diamond (Skretting, Nutreco, Canada, CP = 57%, CL = 15%, CD4). The UNCW‐formulated diet 1 (D1) contained high fish meal (FM, 40% of diet), whereas UNCW‐formulated diet 2 (D2) replaced 50% FM protein by high‐quality poultry by‐product meal (PBM) protein. Post‐metamorphic stage black sea bass (~0.60 g, d40ph) were stocked in each of sixteen 75‐L tanks at a density of 1 fish per L (75 per tank), with four replicate aquaria per treatment. Fish were fed four times per day (0800, 1100, 1400, and 1600 h) to apparent satiation for 30 days. Final body weight (5.70–5.74), specific growth rate (7.40–7.45%/d), and percent body weight gain (834–848%) of fish fed the UNCW‐formulated D1 (FM‐based) and D2 (FM + PBM‐based) were higher (p < .05) than in fish fed the commercial diets CD3 and CD4 (4.66–5.21 g, 6.80–7.15%/d, and 668–756%, respectively). Feed intake (% body weight/d was significantly lower for fish fed commercial diet (CD4) (3.94) compared with fish fed CD3 (4.20), but feed intake for CD3 was not significantly different compared with the UNCW‐formulated diets D1 and D2 (4.10–4.12). Feed conversion ratios (0.76–0.82) were significantly higher for fish fed CD3 (0.82) than for fish fed D1 and CD4 (0.76). Survival was high (99–100%) in all diet treatments. Final whole‐body crude protein content (15.2 to 15.9% wet basis), moisture (68.9–69.6%), and ash (4.31–4.77%) showed no significant differences; however, whole‐body crude lipid was lower in fish fed CD3 (9.67%) than in fish fed the other diets (9.96–10.22%). Final whole‐body fatty acid composition reflected the diet composition. Higher feed consumption and growth of fish fed the UNCW‐formulated diets were attributed to a more optimal combination of marine (fish, squid, and krill meals), terrestrial plant (soybean meal) protein sources, and the addition of chemo‐attractants, which provided both higher nutritional quality and palatability. The study suggests that the species‐specific starter diets may improve growth performance and fingerling quality and may therefore lower production costs under intensive nursery conditions.

Probiotic yeast enhances growth performance of Nile tilapia (Oreochromis niloticus) through morphological modifications of intestine

Probiotics, an eco-friendly alternative to antibiotics application appears to have strong potential for improving the sustainability of aquaculture. The aim of the study was to evaluate the effect of probiotic brewer’s yeast, Saccharomyces cerevisiae supplementation on growth performance, feed utilization and intestinal morphometry of Nile tilapia, Oreochromis niloticus. A feeding trial of 60 days was conducted in which tilapia fingerlings (7.55 ± 1.25 g) were randomly distributed into three replicate aquaria under four different treatment groups, receiving S. cerevisiae at 0, 1, 2 and 4 g kg−1 diet, respectively. At the end of the feeding trial, growth performance parameters (weight gain, WG; % WG; specific growth rate, SGR), feed utilization indices (protein efficiency ratio, PER; feed conversion ratio, FCR) and intestinal morphology were assessed. The results obtained from this study revealed that growth performance and feed utilization indices were increased significantly in the fish fed with 4 g kg−1S. cerevisiae supplemented diet compared to controls. The length, width and area of villus were significantly enlarged in fish fed 4 g kg−1S. cerevisiae supplemented diet. Likewise, intestinal mucosal fold, width of lamina propria, width of enterocytes and number of goblet cells increased in the fish fed with 4 g kg−1S. cerevisiae supplemented diet. These results demonstrated that S. cerevisiae can be effectively recommended as an important growth promoter for tilapia culture.

Effects of African Bentonite on Feed Mycotoxigenic Fungi and Growth of African Catfish Clarias gariepinus

Feed and feed ingredients in the tropics are prone to attacks of mycotoxigenic fungi (myco-fungi) infestation during storage or from the field. The heat applied in feed production destroys only the myco-fungi leaving mycotoxins that eventually end up in the fish. Mycotoxins have negative effects on the growth of fish. It is plausible to reduce or totally eliminate the mycotoxins and myco-fungi by the inclusion of special African bentonite supplement called “Uro’. Five iso nitrogenous and iso energetic feed were made with soybean meal of 12% moisture stored at relative humidity of 78% and temperature 29.45±0.87oC for 30 days. The feed was labelled as F1 to F5 and varied in inclusion levels of bentonite supplement as follows, F1, 34%, F2, 25%, F3, 15%, F4, 5% and F5, 0%. The protein supplement and basal ingredients in the diets were same. Feed ingredients were weighed, mixed, conditioned and pelleted. The feed was dried at 40oC for 24 hours and subjected to mycological analysis. African catfish fingerlings of average weight 6.5±0.36 g were stocked at 15 fish per three replicate aquaria per feed type. Fish were fed to satiation twice daily for 140 days. The catfish fed with F1(35% bentonite) had the best food conversion ratio, 1.63±0.15, highest SGR 5.7±0.05% day1 , weight gain 45.7±3.65g, protein efficiency ratio 1.19±0.10 and highest gut weight 3.46±0.45g. All growth and nutritional parameters were increasing with increasing inclusion of bentonite. Mycological analyses showed that three myco-fungi, namely Aspergilus flavus, Mucor mucedo and Cladosporium cladosporioides were prevalent in the feed. However, feed 1 to feed 3, were completely free from myco-fungi, while feed 4 had traces of M. mucedo and C. Cladosporioides but all myco-fungi were prevalent in F5. African bentonite is calcinated and sequestered feed ANF, myco-fungi and mycotoxins. Bentonite increased digesta viscosity which enabled better digestion of feed, lower FCR, enhanced alkaline intestine for protein and fatty acid absorption. Bentonite increased catfish total glycerides and cholesterol but reduced AST and ALT of the catfish.

Naproxen affects multiple organs in fish but is still an environmentally better alternative to diclofenac

The presence of diclofenac in the aquatic environment and the risks for aquatic wildlife, especially fish, have been raised in several studies. One way to manage risks without enforcing improved wastewater treatment would be to substitute diclofenac (when suitable from a clinical perspective) with another non-steroidal anti-inflammatory drug (NSAID) associated with less environmental risk. While there are many ecotoxicity-studies of different NSAIDs, they vary extensively in set-up, species studied, endpoints and reporting format, making direct comparisons difficult. We previously published a comprehensive study on the effects of diclofenac in the three-spined stickleback (Gasterosteus aculeatus). Our present aim was to generate relevant effect data for another NSAID (naproxen) using a very similar setup, which also allowed direct comparisons with diclofenac regarding hazards and risks. Sticklebacks were therefore exposed to naproxen in flow-through systems for 27 days. Triplicate aquaria with 20 fish per aquarium were used for each concentration (0, 18, 70, 299 or 1232 μg/L). We investigated bioconcentration, hepatic gene expression, jaw lesions, kidney and liver histology. On day 21, mortalities in the highest exposure concentration group unexpectedly reached ≥ 25 % in all three replicate aquaria, leading us to terminate and sample that group the same day. On the last day (day 27), the mortality was also significantly increased in the second highest exposure concentration group. Increased renal hematopoietic hyperplasia was observed in fish exposed to 299 and 1232 μg/L. This represents considerably higher concentrations than those expected in surface waters as a result of naproxen use. Such effects were observed already at 4.6 μg/L in the experiment with diclofenac (lowest tested concentration). Similar to the responses to diclofenac, a concentration-dependent increase in both relative hepatic gene expression of c7 (complement component 7) and jaw lesions were observed, again at concentrations considerably higher than expected in surface waters. Naproxen bioconcentrated less than diclofenac, in line with the observed effect data. An analysis of recent sales data and reported concentrations in treated sewage effluent in Sweden suggest that despite higher dosages used for naproxen, a complete substitution would only be expected to double naproxen emissions. In summary, naproxen and diclofenac produce highly similar effects in fish but the environmental hazards and risks are clearly lower for naproxen. Hence, if there are concerns for environmental risks to fish with diclofenac, a substitution would be advisable when naproxen presents an adequate alternative from a clinical point-of-view.

Effects of α‐ketoglutarate on growth performance, antioxidant capacity and ammonia metabolization against chronic carbonate alkalinity stress in Songpu mirror carp (Cyprinus carpioSongpu)

A 3 × 2 factorial experiment was conducted to investigate the interaction between carbonate alkalinity and dietary α-ketoglutarate (AKG) levels on the growth performance, antioxidant capacity and ammonia metabolization of Songpu mirror carp (Cyprinus carpio Songpu). Each diet (0%, 1% AKG) was randomly allotted to 0 mmol/L, 15 mmol/L, 30 mmol/L carbonate alkalinity groups with three replicate aquaria. The weight gain rate (WGR) significantly increased in the 1% AKG group and significantly decreased with increasing carbonate alkalinity (p < .05). Crude ash was significantly affected by the interaction between carbonate alkalinity and dietary AKG levels and significantly increased in the 1% AKG group (p < .05). A significant interaction between carbonate alkalinity and dietary AKG levels on superoxide dismutase (SOD) activities in hepatopancreas was observed (p < .05). The increasing carbonate alkalinities significantly decreased SOD activities in the hepatopancreas and foregut, catalase (CAT) activities in the hepatopancreas, foregut, midgut and hindgut and glutathione (GSH) contents in the hepatopancreas and foregut (p < .05). Despite AKG addition, the blood ammonia content still increased with increasing carbonate alkalinities. The gene expressions of AQP3, Rhag, Rhcg2 and Na+/K+-ATPase (NKA) in the gills and glutamine synthase (GS) in the brain were significantly upregulated with increasing carbonate alkalinities (p < .05). In the 1% AKG group, GS gene expression significantly upregulated in the brains, whereas AQP3, Rhag, Rhcg2 and NKA gene expressions significantly downregulated in the gills (p < .05). In summary, the 1% AKG addition can enhance the gene expression of ammonia metabolization and improve the antioxidant capacity of Songpu mirror carp with chronic carbonate alkalinity stress.

IMPACTS OF FISH MEAL REPLACEMENT WITH FERMENTED ANIMAL BY-PRODUCTS IN AFRICAN CATFISH (CLARIAS GARIEPINUS) DIETS ON GROWTH, BODY COMPOSITION, AND FISH QUALITY

This study was conducted to evaluate the effect of partial substitution of fish-meal (FM) with two types of fermented animal by-products (fish and poultry offal’s wastes) on growth performance, microbiological, and fish quality of African catfish (Clarias gariepinus). Fish offal’s silage (FOS) and poultry offal’s silage (POS) were fermented by Lactobacillus acidophilus. Five isonitrogenous (34.3% crude protein) diets were formulated to comprise two levels of fermented fish offal (20% and 40%), two levels of fermented poultry offal (20% and 40%) wastes, and 100% fish meal as a control. Ninety hatcheries bred African catfish were randomly distributed into 5 equal groups every 18 fish in three replicate (6 fish/ replicate aquaria). Each of the diets was fed to triplicate groups of African catfish with mean initial weight (MIW) 52g ± 0.01 at 5% body weight in glass aquaria (30 x 30 x70 cm) twice daily (morning and evening) for 12 weeks. The results showed that fish in the fourth group fed on diet supplemented with 20 % POS recorded the best feed conversion ratio (FCR) (1.77±0.1), protein efficiency ratio (PER) (3.51±0.06), incidence of cost (IC) (16.3±0.37), and profit index (PI) (3.51±0.06). Fish in group four as well had the least total bacterial count, coliform, and mold & yeast. The least lactic acid bacteria count and the best overall acceptance were detected also in the fourth group as compared to other groups except diet 1(control) which means it can be used safely without significantly affecting public health or consumer acceptance.

The effect of weaning diet type on grey mullet (Mugil cephalus) juvenile performance during the trophic shift from carnivory to omnivory

In captive grey mullet (Mugil cephalus) juveniles, the weaning stage overlaps the period where there are changes in the ontogeny of digestive enzymes as the fry transit from carnivory to omnivory. The aim of this study was to evaluate growth, survival, weight distribution and the activity of pancreatic and brush border digestive enzymes when fry are fed a carnivorous, herbivorous or omnivorous weaning diet.Fifteen 17-L aquaria in a flow through system with 40‰, UV treated, temperature (24.5 ± 0.5 °C) controlled seawater were stocked with eighty-five 23 dph grey mullet larvae per aquarium. This allowed the testing of three weaning dietary treatments, differing in their protein and carbohydrate content, in 5 replicate aquaria per treatment from 24 to 53 dph. Diet 1 was the dried macroalgal species Ulva lactuca and was designated as a low protein: high carbohydrate herbivorous diet. Diet 2 was a commercial microencapsulated starter feed designated as a high protein: low carbohydrate carnivorous diet. Diet 3 was a 1:1 ww mixture of diets 1 and diet 2 representing an omnivorous feeding regime.The average final weight of the omnivorous feeding fish was significantly (P < .05) higher (203.9 ± 10.0 mg dry weight, dw) than their carnivorous (163.3 ± 7.1 mg dw) and herbivorous feeding (111.8 ± 14.0 mg dw) cohorts. The population of fish fed the herbivorous diet demonstrated a significantly (P = .02) higher percentage of smaller fish (<100 mg) than the omnivorous and carnivorous feeding fish. In contrast, there was a markedly (P = .008 and P = .001) higher percentage of larger (200–400 mg) fish from the carnivorous and omnivorous treatments, respectively, than fish fed the herbivorous diet. Pancreatic α-amylase, alkaline protease and trypsin activity significantly rose when dietary carbohydrate increased, whereas chymotrypsin and lipase activities were independent of the type of diet (P > .05). The activity levels of brush border alkaline phosphatase and intracellular leucine alanine peptidase were similar in grey mullet fry fed the carnivorous and omnivorous diets, but were higher than those in fish fed the herbivorous diet (P < .05). The intestinal maturation index exhibited the highest and lowest values in mullet fry fed the carnivorous and herbivorous diets, respectively, whereas those from the omnivorous group showed intermediate values (P = .03). This study broadly suggests that aquaculture feeds for juvenile grey mullet should be designed for omnivorous feeding habits.

Native Herbivores Improve Sexual Propagation of Threatened Staghorn Coral Acropora cervicornis

Staghorn coral Acropora cervicornis was once spatially dominant on Caribbean reefs but is now threatened throughout its range. In recent years, advancements in ex-situ sexual propagation of Caribbean corals have increased the viability of this management strategy. Thus, improving culture methods for sexually propagated corals is important to bolster the overall coral restoration portfolio and increase genetic diversity in restored populations. In both natural systems and culture scenarios, algae proliferation negatively impacts coral growth and survival. Growing coral with native herbivores may represent a strategy for increased efficiency. We tested A. cervicornis recruits raised in replicate aquaria with identical densities of juvenile Lithopoma americanum or juvenile Batillaria minima snails plus a no-snail control. Each of three replicates per treatment contained tiles with similar numbers of recently settled, visually healthy, A. cervicornis. Tiles were photographed every three weeks for five months and coral growth, survivability, turf algae cover, and crustose coralline algae (CCA) cover were quantified. Labor time for cleaning was carefully recorded for each treatment. Results indicated improved growth and survival when A. cervicornis recruits were raised with either snail species in comparison to a no-herbivore control. Further, including snails decreased labor and eliminated turf algae cover. Interestingly, L. americanum significantly reduced CCA cover relative to the other treatments. We report some of the highest survival rates observed to date for sexually propagated Atlantic corals. Ultimately, results suggest that rearing sexually propagated A. cervicornis with native herbivores could improve the ability to employ these corals in reef restoration.

Effect of fishmeal and fish oil replacement by algal meals on biological performance and fatty acid profile of hybrid striped bass (Morone crhysops ♀ × M. saxatilis ♂)

A 6-week growth trial was conducted to assess the replacement of fishmeal (FM), soy protein concentrate (SPC) and fish oil (FO) by Arthrospira sp. and Schizochytrium limacinum meals in diets for hybrid striped bass (Morone chrysops × M. saxatilis) juveniles of 10.6 ± 0.2 g initial individual weight (±standard deviation). A control diet was formulated with equivalent contributions of FM and SPC to provide 40% crude protein. Menhaden FO was the main lipid source, providing 10% crude fat. Five experimental diets replaced 10, 20, 30, 40 and 50% of FM, SPC, and FO from the control diet by combining two algal meals derived from the freshwater autotroph Arthrospira sp. and the marine heterotroph S. limacinum. Each diet was randomly assigned to three replicate aquaria, and twelve group-weighed fish were stocked per aquarium. Fish were group-weighed weekly to adjust the feeding ration, which started at 6% and gradually decreased to 3%, confirmed by visual feeding cues to avoid overfeeding. At the end of the trial, no statistical differences for responses such as condition factor (P = 0.6778), hepatosomatic index (P = 0.4542), intraperitoneal fat ratio (P = 0.0997), or feed efficiency (P = 0.2210) were detected. However, statistically significant differences were observed for percent weight gain (WG; P = 0.0323) and thermal growth coefficient (TGC; P = 0.0164). Weight gain (209.5%) and TGC (0.088) of fish fed the control diet was significantly lower than in fish fed the 30 and 50% replacement diets (WG: 232.8–235.3%), but no differences were detected among fish fed any other replacement level (WG: 217.1–227.9%). Whole-body proximate composition showed no statistical differences among fish for crude protein, moisture, or ash, except for crude fat content (P < 0.0001); the highest percentage of fat (9.3%) was observed in fish fed the 30% replacement level. The dietary fatty acid profile influenced the fatty acid profile of fish, eliciting an increment in the content of specific fatty acids, such as 16:0, 18:2n-6 and 22:6n-3. Although higher docosahexaenoic acid (DHA) content was observed in whole-body of hybrid striped bass fed the experimental diets, this fatty acid did not contribute to a higher body lipid content. The findings indicate that the combination of Arthrospira sp. and S. limacinum meals can replace a significant proportion of fish-derived feedstuffs in hybrid striped bass feeds, promoting suitable growth performances with up to 50% replacement under these conditions, and promoting the accumulation of DHA in fish tissues, which would ultimately benefit consumers.

Effect of temperature on gonadal growth and maturation of Paracentrotus lividus (Lamarck, 1816)

Effect of temperature on gonadal growth and maturation of Paracentrotus lividus (Lamarck, 1816)

Constant Flux of Spatial Niche Partitioning through High-Resolution Sampling of Magnetotactic Bacteria.

Magnetotactic bacteria (MTB) swim along magnetic field lines in water. They are found in aquatic habitats throughout the world, yet knowledge of their spatial and temporal distribution remains limited. To help remedy this, we took MTB-bearing sediment from a natural pond, mixed the thoroughly homogenized sediment into two replicate aquaria, and then counted three dominant MTB morphotypes (coccus, spirillum, and rod-shaped MTB cells) at a high spatiotemporal sampling resolution: 36 discrete points in replicate aquaria were sampled every ∼30 days over 198 days. Population centers of the MTB coccus and MTB spirillum morphotypes moved in continual flux, yet they consistently inhabited separate locations, displaying significant anticorrelation. Rod-shaped MTB were initially concentrated toward the northern end of the aquaria, but at the end of the experiment, they were most densely populated toward the south. The finding that the total number of MTB cells increased over time during the experiment argues that population reorganization arose from relative changes in cell division and death and not from migration. The maximum net growth rates were 10, 3, and 1 doublings day-1 and average net growth rates were 0.24, 0.11, and 0.02 doublings day-1 for MTB cocci, MTB spirilla, and rod-shaped MTB, respectively; minimum growth rates for all three morphotypes were -0.03 doublings day-1 Our results suggest that MTB cocci and MTB spirilla occupy distinctly different niches: their horizontal positioning in sediment is anticorrelated and under constant flux.IMPORTANCE Little is known about the horizontal distribution of magnetotactic bacteria in sediment or how the distribution changes over time. We therefore measured three dominant magnetotactic bacterium morphotypes at 36 places in two replicate aquaria each month for 7 months. We found that the spatial positioning of population centers changed over time and that the two most abundant morphotypes (MTB cocci and MTB spirilla) occupied distinctly different niches in the aquaria. Maximum and average growth and death rates were quantified for each of the three morphotypes based on 72 sites that were measured six times. The findings provided novel insight into the differential behavior of noncultured magnetotactic bacteria.

Supplementation of organic acids and algae extracts in the diet of red drum Sciaenops ocellatus : immunological impacts

The evaluation of a wide variety of immunostimulatory compounds in the diet of cultured fish has received heightened attention in recent years. However, two organic acids, polyhydroxybutyrate (PHB) and potassium diformate (KDF), have been researched to only a limited extent with aquatic species but have been shown to have various positive effects on terrestrial animals. Two algae extracts, carrageenan and alginic acid, also have been shown to elicit immunostimulation in some fish. Therefore, this study was conducted with red drum, Sciaenops ocellatus, as a model marine species to study the effects of organic acids and algae extracts as feed supplements by evaluating several humoral and cellular immune responses. A 7-week feeding trial was conducted with disease-free juvenile red drum (average initial wt. 2.6 ± 0.2 g). Semipurified diets were formulated to be isocaloric and contain 40% crude protein. Based on previous studies with other fish species, experimental diets were produced by supplementing the basal diet with KDF at 0.6%, PHB at 2%, alginic acid at 1% or carrageenan at 0.5% by weight in place of cellulose. Fish were stocked into 110-L aquaria operated as a recirculating system with each diet assigned to three replicate aquaria containing 15 fish. At the end of 7 weeks, weight gain and feed efficiency were significantly (P < 0.0001) reduced in fish feed PHB compared to the basal diet and both algae extracts. The greatest phagocytic activity was found in fish fed the diet containing PHB. Total immunoglobulin level was higher in fish fed the diet supplemented with carrageenan. Goblet cell proliferation was greatest in the posterior end of the gastrointestinal tract but not different among dietary treatments. Organic acids and algae extracts evaluated in this study produced variable immunological responses in red drum with carrageenan showing the greatest potential as an immunostimulant.

The effect of astaxanthin on resistance of juvenile prawns Macrobrachium nipponense (Decapoda: Palaemonidae) to physical and chemical stress.

In recent years, the use of new scientific techniques has effectively improved aquaculture production processes. Astaxanthin has various properties in aquaculture and its antioxidant benefits have been closely related to stress resistance; besides, it is an essential factor for growth in many crustaceans and fish. The objective of this study was to evaluate the resistance of prawn (Macrobrachium nipponense) fed diets containing different amounts of astaxanthin (AX) to the shock and stress of different physicochemical environments. A 70-day trial was conducted to evaluate the effect of supplementation of a source of astaxanthin (Carophyll Pink, 10% astaxanthin, w/w, Hoffman-La Roche, Switzerland) at various levels in the diet of M. nipponense juveniles. Four dry diets were prepared: AX0 without astaxanthin, AX50 with 50 mg/kg, AX100 with 100 mg/kg, and AX150 with 150 mg/kg astaxanthin. The feeding trial was conducted in a recirculation water system consisting of 12 fiberglass tanks (1000L) used for holding prawns. Three replicate aquaria were initially stocked with 36 org/m2 per tank. During the trial, prawns were maintained on a 12:12-h light:dark photoperiod with an ordinary incandescent lamp, and the water quality parameters were maintained as follows: water temperature, 25-26°C; salinity, 1 g/L; pH, 8.5-8.8; dissolved oxygen, 6.0-6.5 mg/L; and ammonia-nitrogen, 0.05 mg/L. Incorporation of AX, production output, and physiological condition were recorded after 10 weeks of feeding. At the end of the growing period, the prawns were exposed to thermal shock (0°C), ammonia (0.75 mg/L), and reduced oxygen (0.5 mg/L). The time to lethargy and the time to complete death of the prawns were recorded. The results showed that control prawns had the shortest time to lethargy and death compared with prawns subjected to the other treatments. The results of this study have shown that the amount of muscle tissue and gill carotenoids in prawn fed with an AX150 diet showed greater reduction than those exposed to other treatments. It is possible that higher levels of astaxanthin in the body under oxygen reduction stress can be beneficial for prawns. These results suggest that male prawns showed lethargy earlier than females, and the percentage of carotenoid reduction in muscle and gill tissues was higher in males.

Growth and Stress Resistance of Advanced Sized Nile Tilapia Fed Diets Containing Fuel-Based DDGS and Yeast

A feeding trial investigated the use of a diet comprised of yeast and distillers' dried grain with solubles (DDGS) to improve growth, feed utilization, and stress resistance of tilapia. Six diets were formulated (as-fed basis) with 8% menhaden fishmeal and 20%, 25%, or 30% DDGS with or without 0.125% yeast probiotic. Aquaria (110 L) were stocked with eight Nile tilapia (mean weight = 43.6 ± 1.3 g) with four replicate aquaria per diet. Weight gains, food conversion ratios (FCR), protein efficiency ratios (PER), blood cortisol levels, and survival rates did not significantly differ (P ≥ 0.1) among or between fish fed differing diets. Overall, results indicated that the inclusion of low-level yeast probiotics did not increase the utilization of DDGS nor did it improve the growth or acute stress resistance (i.e., short-term stressor) of juvenile Nile tilapia.

Effect of light intensity on first feeding of the chub mackerel Scomber japonicus larvae

This study investigated the effect of different light intensities on first feeding of chub mackerel Scomber japonicus larvae. Fertilized eggs, obtained from LHRHa-induced spawning of captive broodstock, were stocked (60 larvae/l) into twelve 30-l aquaria under light intensities of 0, 100, 200, 500 and 1000 lx, with three replicate aquaria per treatment. Temperature was maintained at 20°C and salinity was 35 psu. Larvae were fed the rotifer Brachionus rotundiformis at a density of five rotifers/ml. Feeding incidence was measured as the percentage of larvae with prey in the digestive tract. Feeding intensity was evaluated as the number of prey in the digestive tract of the larvae. Larvae fed in darkness (0 lx) had significantly lower (P<0.05) feeding incidence (13±0.05% larvae with prey) and feeding intensity (1.00±0.05 rotifers per larva) than those larvae fed at 100 (30±0.07%, 1.17±0.09 rotifers per larva), 200 (43±0.08%, 1.24±0.11 rotifers larvae−1), 500 (53±0.08%, 1.48±0.14 rotifers per larva) and 1000 lx (60±0.08%, 1.38±0.13 rotifers per larva). The feeding incidence of S. japonicus larvae increased with light intensity while feeding intensity showed no significant difference (P>0.05) between light treatments.

Sensitivity of the seagrass Cymodocea nodosa to hypersaline conditions: A microcosm approach

Marine water desalination is an emergent strategy to satisfy water demand in coastal regions. The brine originated as a by-product (60–90 psu) can have a significant impact on important marine ecosystems, yet the tolerance thresholds of most key species remain unknown. Therefore, with the aim of filling this gap and providing useful information to mitigate such impacts, we have experimentally assessed the response to hypersaline conditions of the seagrass Cymodocea nodosa. We exposed plants in microcosms to 4 treatments: control (37.2 psu), 44 psu, 54 psu and 62 psu, with three replicate aquaria per treatment for 17 days, and we measured plant response and status. We found that the seagrass shoots endured 44 psu without any apparent damage, but vitality decreased in 54 and 62 psu treatments. Plants at both 54 and 62 psu displayed reduced leaf growth and higher incidence of leaf necrosis, relative to control conditions. In addition, in plants at 62 psu, photosynthetic performances (measured as leaf quantum efficiency) dropped shortly after salt addition, and by the end of the experiment they also suffered substantial mortality. These findings should be viewed with caution, due to the relatively short time-span of the experiment, as in the long-term plants may be less tolerant than reported here. However, our results highlight the need for careful management of brine disposal to prevent deterioration of seagrass habitats; salinity should never exceed 44 psu inside the meadows, to prevent deterioration of C. nodosa habitats.

Mortality Rates in Golden Shiners Fed High‐Fat Diets with or without a Dairy‐Yeast Prebiotic before Challenge with Flavobacterium columnare

AbstractColumnaris, caused by Flavobacterium columnare, is a major bacterial disease of the golden shiner Notemigonus crysoleucas, especially when fish become stressed during handling and transport. Feed additives, such as a dairy‐yeast prebiotic, can decrease disease susceptibility in some fish species. Previous studies have indicated that diets with higher fat concentrations have improved the growth and survival of golden shiners. We conducted a study to determine whether a high‐fat diet alone or supplemented with a dairy‐yeast prebiotic could decrease mortality rates of golden shiners subjected to columnaris challenge. Golden shiners were assigned one of three diets with four replicate aquaria per diet and fed to apparent satiation twice daily for 16 weeks before the challenge. Diets (30.3 ± 0.31% crude protein; mean ± SE) were similar to a commercial formula and contained (1) 4% poultry fat (control), (2) 10% poultry fat, or (3) 10% poultry fat and 2% dairy‐yeast prebiotic. After the 16‐week feeding period, 15 golden shiners (2.2 ± 0.03 g) from each aquarium were stocked into different aquaria (experimental replicates were maintained) and exposed to 20 mL of columnaris bacteria in Sheih broth (optical density, 0.395 Å; at 560 nm; Sheih broth blank) for 18 h. Kidney cultures taken from moribund fish were streaked on Sheih agar to confirm the presence of columnaris and an active infection. Mortality in the 4% poultry fat (41.7 ± 12.9%) and 10% poultry fat (40.0 ± 6.1%) diets was high and not significantly different. Mortality for the dairy‐yeast prebiotic (6.7 ± 2.7%) diet was much lower and significantly different from that for the 4% and 10% poultry fat diets. Thus, the dairy‐yeast prebiotic effectively reduced mortality rates in golden shiners exposed to columnaris, but a high‐fat diet alone provided no protection relative to the lower‐lipid control diet.

Effects of stocking density on the survival, growth, size variation and condition index of juvenile rabbitfish Siganus rivulatus

Spinefoot rabbitfish, Siganus rivulatus, is an economically important species of herbivorous fish that is relatively easy to rear and thus considered to be suitable for aquaculture. Juveniles are generally reared in nursery systems before being stocked into growout cages or ponds. We report here our evaluation of the effects of stocking density on the survival, growth, feed efficiency and condition index of S. rivulatus juveniles in nursery tanks. The experiment was conducted in a recirculating system of twelve 52-l aquaria connected to a biological filter and a sand filter. Juvenile fish (average weight 6.5 g) were stocked into aquaria at four stocking densities (10, 20, 30, and 40 fish/aquarium) with three replicate aquaria per treatment. Diet was provided at 3% body weight daily divided into two feedings. Fish were weighed weekly for 8 weeks and the diet increased accordingly. Survival was greater than 95% in all treatments, with no significant differences observed among treatments. There were also no differences in specific growth rate (SGR 2.12-2.27) of the fish among treatments. Growth rate was linear during the 8 weeks in all treatments, and harvested biomass increased propor- tionally to stocking density (198, 401, 600 and 785 g per increasing stocking density, respectively). Feed efficiency (FE 0.67-0.71) of the fish did not vary significantly among treatments. The coefficient of variation was high (35-41%) among the harvested fish, but it also did not differ significantly among treatments. The final condition indices of the fish in all treatments were similar to each other but significantly greater than the initial values (P \ 0.05). The results suggest that there is no apparent effect of stocking density at the levels tested on the survival and growth of juvenile rabbitfish.

Effect of Dietary Lipid Level and Protein Energy Ratio on Growth and Body Composition of Largemouth Bass Micropterus salmoides

A feeding trial was conducted in aquaria with juvenile largemouth bass Micropterus salmoides to examine the effects of increasing dietary lipid levels on growth and body composition. Feed-trained largemouth bass fingerlings were graded to a similar size (16.3 ± 2.4 g) and randomly stocked into 15 113.6-L glass aquaria at 25 fish/aquarium. Fingerlings were fed twice daily to apparent satiation with one of five isonitrogenous extruded experimental diets based on practical ingredients. Diets contained approximately 40% crude protein and either 0, 5, 10, 15, or 20% added lipid. Due to background lipids in the ingredients, this equated to total lipid levels of 7, 10, 16, 20, and 23%, respectively. These diets had protein to energy ratios of 137, 120, 106, 95, and 86 mg/kcal, respectively. There were three replicate aquaria per dietary treatment. After 12 wk, there were no statistically significant differences (P > 0.05) in average weight (g), specific growth rate (% body weight/d), survival (%), or protein efficiency ratio (PER, %) among fish fed the five diets, which averaged 79.3 ± 5.6, 1.9 ± 0.1, 99.5 ± 1.5, and 2.11 ± 0.19, respectively. Juvenile largemouth bass fed diets containing 15 and 20% added lipid had significantly lower (P± 0.05) feed conversion ratios (FCR) (1.1 ± 0.0 and 1.1 ± 0. 1, respectively) than fish fed diets containing 0, 5, and 10% added lipid (1.4 ± 0.1, 1.3 ± 0. 1, and 1.3 ± 0.2, respectively). Proximate analysis of whole body samples indicated a significantly higher (P ± 0.05) lipid content in fish fed 15 and 20% added lipid compared to fish fed lower lipid levels. While FCR was lowest in fish fed the 15 and 20% added lipid diets, increased whole body lipid deposition may indicate that these levels are above optimal levels for juvenile largemouth bass. It appears that 7–16% total dietary lipid (P/E:137–106 mg/kcal) is sufficient to support efficient growth without impacting body composition in juvenile largemouth bass when fed a diet containing 40% crude protein.

Evaluating the Benefits of Size-Sorting Tilapia Fry Before Stocking

Size-grading is routinely practiced in fish hatcheries for reasons such as increased growth among small fish, reduction of cannibalism, decrease in size variability among harvested fish, and facilitated feeding; yet there is little information with regards to growth potential of sorted groups. Two growth trials were conducted with 30-day-old, size-sorted tilapia, to evaluate growth depensation and the influence of social interactions. In the first experiment, sibling juvenile tilapia were sorted into three size classes, small (2.6 g), medium (3.7 g), and large (4.9 g), and 15 fish were stocked into 60-L aquaria with three replicate aquaria per treatment. A fourth treatment (mixed) consisted of five fish from each size category stocked together. Diet was offered at 5% body weight per day over a 7-week growth trial. Average final weights of the fish at harvest were 13.3, 18.8, 27.0, and 24.7 g for small, medium, large and mixed treatments, respectively. Fish in the large treatment grew faster than fish in the medium treatment, which in turn grew faster than fish in the small treatment. Condition index of fish in the large treatment was significantly greater than in the small treatment (P < 0.05). In the second experiment sex-reversed juvenile tilapia were sorted and divided into small (0.9 g), medium (1.2 g), and large (1.5 g). Methods were as previously described except after eight weeks of culture, the tilapia were harvested and then transferred into larger tanks (150 L) to accommodate for their increased size. Average final weights after 13 weeks were 61.3, 78.8, 95.0, and 75.8 g for small, medium, large, and mixed treatments, respectively. Fish in the large treatment grew significantly faster (P < 0.05) than fish in the medium, small, and mixed treatments. Results suggest that size grading before stocking would improve commercial returns for farmers.