δ13C-δ15N values as indicators of trophic position and competitive overlap for Pacific salmon (Oncorhynchus spp.)

Analysis of δ¹³C and δ¹⁵N isotope values for five species of Pacific salmon indicate that they form a trophic hierarchy on the high seas. On the basis of an analysis of these stable isotope ratios, chinook salmon feed at the upper end of the food chain and pink salmon at the lower end, in the sequence pink → sockeye → coho → chinook, with chinook and pink salmon separated by ca. 0.8 of a trophic level. Chum salmon occupy a peculiar position, with low δ¹³C values and high δ¹⁵N values, possibly reflecting an unusual diet that includes large amounts of gelatinous zooplankton (salps, ctenophoi;s, and medusae). Chum appear to occupy a unique trophic position, at a trophic level nearly as high as that of chinook but at the end of a different branch of the food chain. If true, the potential for trophodynamic competition with other salmon species is small. Our results suggest that the greatest potential for trophodynamic competition occurs within the pink-sockeye-coho grouping. A similar analysis, restricted to five stocks of North American sockeye, shows that four widely separated stocks have similar heavy isotope compositions but that the separation between these stocks is still statistically significant. The Chilko stock is strikingly different, however, suggesting that it is located in the central Gulf of Alaska, a region of intense upwelling. Circumstantial evidence supporting the possibility that the Chilko and other sockeye stocks are geographically separated within the Gulf of Alaska is reviewed.     

Growth performance,survival, feed utilization and nutrient utilization of African catfish (Clarias gariepinus) larvae co‐fed Artemia and a micro‐diet containing freshwater atyid shrimp (Caridina nilotica) during weaning

Problems of limited number of dry feeds as supplement or replacement of live feeds have led to poor larval nutrition in many species of fish. Therefore, the suitability of co‐feeding 8‐day‐old African catfish (Clarias gariepinus) posthatch larvae using live feed (Artemia salina) and formulated dry diet containing freshwater atyid shrimp (Caridina nilotica) during weaning was investigated. The experiment ended after 21 days of culture and respective groups compared on the basis of growth performance, survival, feed utilization and nutrient utilization. Larvae co‐fed using 50%Artemia and 50% formulated dry diet resulted in significantly (P < 0.05) better growth performance, food gain ratio (FGR), protein efficiency ratio (PER) and productive protein values (PPV) than other treatments. The lowest growth performance occurred in larvae weaned using 100% formulated and commercial dry diets. Better survival of over 90% was obtained in larvae weaned using 50%Artemia and 50% dry diet, while abrupt weaning using 100% dry diets resulted in lower survival (<75%). These results support a recommendation of co‐feeding C. gariepinus larvae using a formulated dry diet containing C. nilotica and 50% live feed when weaning is performed after 8 days posthatching period.     

Sea cucumber habitat differentiation and site retention as determined by intraspecific stable isotope variation

Stable carbon and nitrogen isotope ratios (δ¹³C/δ¹⁵N) were assessed as a means to ascertain the recent in situ feeding history of the common New Zealand sea cucumber Australostichopus mollis in relation to nutrient enrichment from a longline green‐lipped mussel (Perna canaliculus) farm in Northern New Zealand. δ¹³C and δ¹⁵N isotopic signatures and the ratios of sea cucumbers sampled from within the impact footprint of the mussel farm were compared with those of sea cucumbers residing on adjacent natural reefs. Sea cucumbers from beneath mussel farming longlines had significantly different δ¹³C stable isotope signatures in comparison with sea cucumbers collected from neighbouring natural reef habitats. This difference supports the hypothesis that sea cucumbers in the same bay maintain distinctly different feeding histories, with those residing beneath mussel farming longlines deriving tissue carbon from sediment impacted by farming activities. This hypothesis is further supported by the finding that the isotope signature of sediment collected from beneath the mussel farm is consistent with the expectation that sea cucumbers were feeding on and consuming sediment enriched with bivalve waste (faeces and pseudo‐faeces). In contrast, the nitrogen stable isotope signature (δ¹⁵N) was found to be similar between sites for both sea cucumbers and assumed food sources. Both findings lend support to the viability of future sea cucumber/green‐lipped mussel farm polyculture systems. Sea cucumbers in different locations (mussel farm, natural reef) possessed distinctly different isotope signatures, suggesting that mixing of sea ranched sea cucumbers with natural reef populations would be negligible or non‐existent. Similarities between the isotope signatures in low metabolic tissue of sea cucumbers residing at the mussel farm site to that of mussel farm‐impacted sediment suggest that cucumbers beneath mussel farms appear to have high rates of retention at the farm site.     

Establishing larval feeding regimens for the Forktail Blenny Meiacanthus atrodorsalis (Günther, 1877): effects of Artemia strain,time of prey switch and co‐feeding period

This study aimed to establish feeding strategies covering the whole larval period of the forktail blenny, Meiacanthus atrodorsalis, based on the standard hatchery feeds of rotifers and Artemia. Three purposely designed experiments were conducted to determine the appropriate times and techniques to transition larvae from rotifers onto Artemia nauplii of a Great Salt Lake (GSL) strain, and a specialty AF strain, as well as subsequent transition onto enriched metanauplii of GSL Artemia. With a 3‐day co‐feeding period, larvae adapted well to a transition from rotifers to newly hatched GSL Artemia nauplii as early as 5 days posthatching (DPH), and as early as 3 DPH when fed the smaller AF Artemia nauplii. However, prolonging the rotifer‐feeding period up to 11 DPH did not negatively affect survival. Larvae fed Artemia nauplii of the AF strain showed 17–21% higher survival, 24–33% greater standard length and body depth, and 91–200% greater dry weight, after 20 days relative to those fed nauplii of the GSL strain. Meanwhile, enriched Artemia metanauplii of the GSL strain were shown to be an acceptable alternative to AF Artemia nauplii for later larvae, producing similar survival and growth when introduced from 8 DPH. Based on our findings, we recommend feeding M. atrodorsalis larvae rotifers as a first food between 0 and 2 DPH, introducing AF Artemia nauplii from 3 DPH, followed by enriched GSL Artemia metanauplii from 8 DPH onward, with a 3‐day co‐feeding period between each prey change.     

Daily food intakes and optimal food concentrations for red king crab (Paralithodes camtschaticus) larvae fed Artemia nauplii under laboratory conditions

Daily food intakes, optimal feeding regimes and food concentrations for laboratory reared Paralithodes camtschaticus (Tilesius, 1815) larvae were investigated. Artemia nauplii hatched at standard conditions were used as food. Daily food intakes of zoeae I–IV at 7–8 °C comprised 11.3, 22.4, 33.2, and 41.8 nauplii individuals (ind)^?1 day^?1, respectively, taking into account that wet weight of Artemia nauplii used for the experiments constituted 0.026 mg, dry weight 0.0042 mg. Optimal initial Artemia nauplii concentrations for feeding zoeae I–IV was determined as 400–600, 600–800, 800–1000 and 1000–1200 nauplii L^?1 respectively. Recommendations on using Artemia nauplii as food for red king crab larvae were outlined on the basis of experimental results. Growth, development and survival rates of zoeae I–IV reared in recycling water system at 7–8 °C and fed Artemia nauplii according to these recommendations were described.     

Ecological influences on the difference in δ15N and δ13C values between fish tissues: implications for studies of temporal diet variation

Temporal diet changes can be detected by comparing δ¹³C and δ¹⁵N values between tissues with different isotopic turnover times. However, other factors contribute to disparities in δ¹³C and δ¹⁵N signatures between tissues and could confound the interpretation of stable isotope data. We examined the effects of ecological factors on differences in muscle and liver δ¹³C and δ¹⁵N signatures of Arctic charr [Salvelinus alpinus, (L.)] to determine whether their effects were large enough to influence studies of diet change. In addition, we examined whether differences in lipid content accounted for a significant portion of the differences in δ¹³C values between tissues. Results indicated that life history, diet, reproductive status and gender had significant effects on the differences in δ¹³C values between tissues, while gender and diet significantly affected differences in δ¹⁵N values. Differences in % lipid content between tissues also explained approximately 74% of the observed variation in the difference in δ¹³C values between tissues. The differences in δ¹³C values observed between muscle and liver tissues may be partially explained by physiological differences in lipid storage and use between tissues associated with ecological factor effects. These results demonstrate that ecological factors other than a change in diet can influence the differences in δ¹³C and δ¹⁵N signatures between muscle and liver tissues. However, the impact of ecological factors on studies of diet change depends on how the magnitude of the factor effects compared with a biologically meaningful change in diet.     

Tissue‐specific stable isotope ratios of shortfin mako (Isurus oxyrinchus) and white (Carcharodon carcharias) sharks as indicators of size‐based differences in foraging habitat and trophic level

We evaluated whether the trophic level and feeding grounds (coastal versus offshore) of white and shortfin mako sharks captured in the northern Mexican Pacific varied as a function of size using carbon (δ¹³C values) and nitrogen (δ¹⁵N values) stable isotope analysis of soft tissues. A step increase in δ¹⁵N values was observed at approximately 85 cm TL and 150–170 cm TL for shortfin mako and white sharks, respectively, consistent with the dilution of the maternal isotopic signal following the incorporation of exogenous food. Shortfin mako and white shark muscle tissue and whole blood were enriched in ¹⁵N as a function of size, which is consistent with increasing trophic level, but this pattern may be confounded by differences in habitat. To infer differences in foraging habitat throughout life, we compared isotope ratios of liver and blood fractions with those of white muscle tissue; these tissues have relatively faster and slower isotope turnover rates, respectively. Whole blood and muscle δ¹³C values of small white sharks (<200 cm total length) caught near the coast suggested benthic foraging. Very limited differences between δ¹³C values of muscle tissue and whole blood from small and medium mako (<196 cm TL) and small white sharks indicated equilibrium to local feeding grounds. In contrast, differences in the δ¹³C values of liver tissue from small and medium mako and small white sharks indicated changes in diet or feeding grounds. The δ¹³C values of plasma and muscle tissue of large white sharks (>350 cm total length) caught offshore indicate feeding in coastal and oceanic areas and are consistent with recent migration to pelagic feeding grounds. Our study provides insight into size‐based habitat use and migration patterns of two species of migratory sharks for which there is limited information, particularly in their nursery grounds in Mexican waters.     

Quantification of waste feed and fish faeces in sediments beneath yellowtail pens and possibility to reduce waste loading by co‐culturing with sea cucumbers: an isotopic study

To evaluate environmental impacts of yellowtail culture and to examine the efficiency of the sea cucumber Apostichopus japonicus in reduction of waste loading, surface sediments were sampled and A. japonicus were cultured at a yellowtail farm in Owase Bay, Japan. Waste feed‐ and faeces‐derived organic matter (WOM, FOM) in sedimentary organic matter (SOM) was estimated based on the δ¹³C and δ¹⁵N of the fish feed (?21.7‰, 9.2‰), yellowtail faeces (?20.6‰, 6.2‰) and SOM reference (?24.4‰, 4.4‰). Small WOM (0–22% in SOM) but substantial FOM (28–61%) loadings in the fish farm area and high sulphide concentrations in the sediments (1.0 mg g^?1) suggest that reduction in the fish stocks or mitigation of the faeces should be considered. A. japonicus juveniles were cultured in three cages deployed below a pen and growth was assessed after three different periods (62, 107, 181 days). A. japonicus grew well during the first 107 days (daily specific growth rate, 3.7%) and their survivorship was high (80–90%). Growth ceased after 107 days, probably due to fouling on the cages. The δ¹³C and δ¹⁵N of their hypothetical diet (–19.7‰, 5.5‰) were close to the FOM values, suggesting assimilation of FOM.     

Effect of Salinity on Larval Rearing of Pacu,Piaractus mesopotamicus,a Freshwater Species

The aim of this study was to evaluate the growth and survival of pacu, Piaractus mesopotamicus, larvae reared in different salinities and to determine the Artemia nauplii life span in freshwater and in saline water. First feeding 5‐d‐old pacu larvae were reared in freshwater or at 2, 4, 6, 8, 10, 12, and 14 ppt salinities. The larvae were reared in 1.5‐L aquaria at a density of 10 larvae/L with three replicates per treatment. After 10 d of rearing, significant differences (P < 0.05) were observed for growth and survival. Larval growth was higher at 2 and 4 ppt, and survival at 2 ppt was 100%. In freshwater and at 4, 6 and 8 ppt, the survival was 91.1, 93.3, 73.3, and 39.9%, respectively. At higher salinities, there was 100% mortality after 2 h (12 and 14 ppt) and 8 h (10 ppt) of exposure. The slightly saline water of at least 2 ppt increased the Artemia nauplii life span compared to the life span in freshwater. Later, in a second trial, 5‐d‐old pacu larvae were reared in freshwater and at 2 and 4 ppt salinities during the first 5 or 10 d of active feeding, and then the fish were transferred to freshwater. At the end of 15 d, larval growth was lower in freshwater (42 mg) than in treatments 2 and 4 ppt (59–63 mg). The abrupt transfer of fish from freshwater to slightly saline water and the return to freshwater did not affect the survival rates (89–97%). The larvae were able to adapt to these saline environments and handle abrupt changes in salt concentration. We concluded that salinity concentration of 2 ppt can be used for pacu larval rearing, allowing the Artemia nauplii lifetime to last longer and cause faster fish growth.     

Relationship between prey utilization and growth variation in hatchery‐reared Pacific bluefin tuna,Thunnus orientalis (Temminck et Schlegel), larvae estimated using nitrogen stable isotope analysis

In mass culture of Pacific bluefin tuna Thunnus orientalis, a marked growth variation is observed after they start feeding at 6–7 mm in body length (BL) on yolk‐sac larvae of other species, and the growth variation in tuna larvae is a factor leading to the prevalence of cannibalism. To examine the relationship between prey utilization and growth variation, nitrogen stable isotope ratios (δ¹⁵N) of individual larvae were analysed. A prey switch experiment was conducted under two different feeding regimes: a group fed rotifers (rotifer fed group), and a group fed yolk‐sac larvae of spangled emperor, Lethrinus nebulosus (fish fed group) from 15 days after hatching (6.87 mm BL). The fish fed group showed significantly higher growth than the rotifer fed group. Changes in the δ¹⁵N of the fish fed group were expressed as an exponential model and showed different patterns from those of the rotifer fed group. The δ¹⁵N of fast‐growing tuna larvae collected in an actual mass culture tank after the feeding of yolk‐sac larvae was significantly higher than those of the slow‐growing larvae, indicating that slow glowing larvae depended largely on rotifers rather than the yolk‐sac larvae.     

Effect of cultivated copepods (Acartia tonsa) in first‐feeding of Atlantic cod (Gadus morhua) and ballan wrasse (Labrus bergylta) larvae

The aim of this study was to compare the nutritional composition and effects of short periods with cultivated copepod nauplii versus rotifers in first‐feeding. Atlantic cod (Gadus morhua) and ballan wrasse (Labrus bergylta) larvae were given four different dietary regimes in the earliest start‐feeding period. One group was fed the copepod Acartia tonsa nauplii (Cop), a second fed enriched rotifers (RotMG), a third fed unenriched rotifers (RotChl) and a fourth copepods for the seven first days of feeding and enriched rotifers the rest of the period (Cop7). Cod larvae were fed Artemia sp. between 20 and 40 dph (days posthatching), and ballan wrasse between 36 and 40 dph, with weaning to a formulated diet thereafter. In addition to assessing growth and survival, response to handling stress was measured. This study showed that even short periods of feeding with cultivated copepod nauplii (7 days) had positive long‐term effects on the growth and viability of the fish larvae. At the end of both studies (60 days posthatching), fish larvae fed copepods showed higher survival, better growth and viability than larvae fed rotifers. This underlines the importance of early larval nutrition.     

Trophic relationships between a native and a nonnative predator in a system of natural lakes

Abstract – Bull trout, a species of char listed as threatened under the US Endangered Species Act, have been displaced from portions of their historic range following the introduction of nonnative lake trout. It has been suggested that competitive exclusion as a result of trophic overlap between bull trout and lake trout may be the causal mechanism associated with displacement of bull trout. This study used stable isotope data to evaluate trophic relationships among native bull trout, nonnative lake trout and other fishes in seven lakes in Glacier National Park (GNP), Montana. Bull trout and lake trout had greater δ¹⁵N values relative to other fishes among lakes (δ¹⁵N ≥ 3.0‰). Lake trout had greater δ¹⁵N values relative to bull trout (δ¹⁵N = +1.0‰). Bull trout had greater δ¹³C values relative to lake trout in six of the seven lakes examined. Although both bull trout and lake trout had greater δ¹⁵N values relative to other fishes within lakes in GNP, differences in δ¹⁵N and δ¹³C between bull trout and lake trout suggest that they are consuming different prey species or similar prey species in different proportions. Therefore, displacement of bull trout as a direct result of complete overlap in food resource use is not anticipated unless diet shifts occur or food resources become limiting. Additionally, future studies should evaluate food habits to identify important prey species and sources of partial dietary overlap between bull trout and lake trout.     

Evaluation of frozen Umbrella‐stage Artemia as first animal live food for Litopenaeus vannamei (Boone) larvae

An alternative larval shrimp feeding regime, in which umbrella‐stage Artemia were constituting the first zooplankton source was evaluated in the culture of Litopenaeus vannamei. In a preliminary experiment, umbrella‐stage Artemia were fed to larvae from zoea 2 (Z2) to mysis 2 (M2) stages to identify the larval stage at which raptorial feeding starts and to determine daily feeding rates. The following experiment evaluated the performance of two feeding regimen that differed during the late zoea/early mysis stages: a control treatment with frozen Artemia nauplii (FAN), and a treatment with frozen umbrella‐stage Artemia (FUA). The ingestion rate of umbrella‐stage Artemia increased from nine umbrella per larvae day^?1 at Z2 stage to 21 umbrella per larvae day^?1 at M2. A steep increase in ingestion and dry weight from Z3 to M2 suggests a shift to a raptorial feeding mode at the M1 stage. Treatment FUA exhibited a significantly higher larval stage index (P < 0.05) during the period that zoea larvae metamorphosed to the mysis stage, and a higher final biomass, compared with treatment FAN. Based on these results and on practical considerations, a feeding regime starting with umbrella‐stage Artemia from Z2 sub‐stage can be recommended for L. vannamei larvae rearing.     

Effect of Rearing Density and Feeding Regimes on Growth and Survival of African Catfish,Heterobranchus longifilis (Valenceinnes, 1840) Larvae in a Closed Recirculating Aquaculture System

Heterobranchus longifilis larvae were reared over a 35 d period to evaluate the effects of stocking densities and feeding regimes on growth and survival. In experiment 1, larvae (12.3?±?2.1 mg) were stocked into glass aquaria at densities of 1, 2, 5, 10, 15, 20, and 25 larvae L^?1. Larvae were fed on Artemia nauplii ad libitum. Significant variations in terms of growth performance and feed utilization occurred at all levels of density treatments. Specific growth rate (SGR), body weight gain (BWG), and feed efficiency (FE) of the larvae decreased significantly as density increased. However, survival rate increased with the increase of stocking density. In experiment 2, larvae (13.4?±?1.1 mg) stocked at a density of 15 larvae L^?1, in the same conditions as experiment 1, were fed on three different regimes: Artemia nauplii; 35%?protein beef brain; and 35%?protein commercial catfish feed (CN⁺). SGR, BWG, and coefficient of variation (CV) of larvae fed on Artemia nauplii were significantly higher than those fed on beef brain and CN⁺. The survival rate of larvae fed on beef brain was significantly higher (88.40?±?9.75%) than those of Artemia (69.21?±?6.69%) and CN⁺ (40.40?±?6.22%). The results of this study suggest that the optimum stocking density is 15 larvae L^?1 and the beef brain can be used as alternative feed to Artemia in rearing H. longifilis larvae.     

Preliminary study on the activity of protease enzymes in Persian sturgeon (Acipenser persicus Borodin, 1897) larvae in response to different diets: effects on growth and survival

The specific activity of alkaline protease, trypsin and pepsin‐like enzymes was measured in yolk sac stage Acipenser persicus larvae and over a 1‐month feeding experiment using live Artemia nauplii (ND), formulated feed (FD) or mixed food (MD). Artemia nauplii group larvae showed significantly higher growth and survival during the first 15 days while FD larvae showed the lowest growth and survival. At day 30, MD larvae exhibited significantly higher growth than the ND group. Alkaline protease activity showed the lowest activity on day 15; the highest activity was observed in the MD group larvae. Pepsin‐like activity showed a drastic increase from day 1 to 5 in all treatments, but remained stable throughout the next 25 days, with the lowest and the highest activity in the FD treatment on day 10 and in the MD treatment on day 30 post‐feeding respectively. Trypsin‐like activity in group ND remained almost the same from day 5 to 30, whereas in groups MD and FD, it decreased significantly from day 10 to 30. The contribution of the naupliar proteases was moderate but effective. Additionally, better performance in Artemia fed sturgeon larvae may also be due to the structure and digestibility of proteins and the food intake stimulation by the nauplii.     

Investigation of geographic origin,salinity and feed on stable isotope profile of Pacific white shrimp (Litopenaeus vannamei)

Increasing numbers of mislabelled seafood products in the globalized market underline the need for approaches to identify the origin of these products. Pacific white shrimp cultured in different salinities (Litopenaeus vannamei) from 16 locations in China and USA were collected and differentiated based on δ¹³C and δ¹⁵N values. The δ¹³C and δ¹⁵N values of 16 commercial feeds used in shrimp culture were measured and effects of feed on C and N stable isotope composition in shrimp were investigated. Carbon and nitrogen isotopic analysis of the shrimp did not provide means to discriminate farmed shrimp from China and USA. However, the shrimp cultured in water with high salinity were enriched in ¹³C compared to shrimp cultured in freshwater and this provided another basis for discrimination. The correlation between δ¹³C in feed and shrimp was not significant, while the δ¹⁵N in feed and shrimp showed a trend of positive correlation.     

Altered sex ratio in giant fresh water prawn, Macrobrachium rosenbergii (de Man) using hormone bioencapsulated live Artemia feed

Artemia nauplii cultured for 24 h in lipid‐enriched media contained 0, 0.38, 1.67, 0.79, 5.71 and 5.14 ng 17α‐methyl testosterone (MT) mg^?1 dry weight for the control, 5, 15, 30, 50 and 100 mg of 17α‐MT L^?1 of media respectively. Giant fresh water prawn Macrobrachium rosenbergii larvae were fed hormone‐enriched Artemia nauplii for 50 days. A significant difference in sex ratios (0.92, 0.69 and 0.93) was obtained in relation to the control group. These results suggest that further research is needed with regard to standardization of doses and duration of treatments for complete hormonal control of sex differentiation in M. rosenbergii.     

Rearing juvenile tench (Tinca tinca L.) under controlled conditions using Artemia nauplii as supplement to a dry diet

A 120-day experiment was performed with 4-month-old juvenile tench [initial mean weight: 0.31 g; total length (TL): 32 mm] to evaluate live Artemia nauplii as supplement to a dry diet for salmonids. All groups received the dry diet. Five treatments, differing in the amount of supplemented Artemia, were tested: without supplement, 450, 900, and 1,800 nauplii g⁻¹ initial fish biomass, and nauplii in excess. Groups that received Artemia supplement had significantly higher survival (between 89.4 and 98.7%) compared to those that received dry diet alone (49.2%), while among them there was no significant difference. Juvenile tench fed the dry diet supplemented with Artemia in excess had a specific growth rate (1.98), weight (3.40 g), and TL (63.90 mm) significantly higher than those in the rest of the treatments. The latter three features were not significantly different under limited co-feeding (450, 900, and 1,800 nauplii g⁻¹ biomass) averaging 1.26 specific growth rate, 1.40 g weight, and 48.50 mm TL. Tench fed the dry diet alone grew significantly less than the rest. Thus, the drawbacks of feeding juvenile tench with dry foods originally formulated for other fish species can be overcome by providing a supplement of Artemia nauplii.     

Effect of Artemia enrichment on the growth and survival of Pacific bluefin tuna Thunnus orientalis (Temminck & Schlegel) larvae

This study was carried out to investigate the suitability of Artemia enriched with docosahexaenoic acid (DHA) and choline as live food on the growth and survival rate of the Pacific bluefin tuna (PBT; Thunnus orientalis) larvae. The PBT larvae were fed either Artemia enriched with oleic acid (Diet 1), DHA (Diet 2), DHA+choline 1.0 mg L^?1 (Diet 3) and DHA+choline 2.0 mg L^?1 (Diet 4) or striped knifejaw larvae (Diet 5, reference diet), in duplicate for 12 days. Enrichment of Artemia with DHA significantly increased the DHA levels to 13.9, 13.8 and 12.5 mg g^?1 on a dry matter basis in Diets 2, 3 and 4 respectively; however, the levels were significantly lower than the reference diet (26.9 mg g^?1 dry matter basis; Diet 5). Although growth and survival rate were significantly improved by the enrichment of Artemia with DHA and choline, the improvement was negligible compared with the enhanced growth and survival rate of the fish larvae‐fed group (P<0.05). The results demonstrated that enriched Artemia does not seem to be the right choice to feed the PBT larvae perhaps because of the difficulties in achieving the correct balance of fatty acid with higher DHA/EPA from Artemia nauplii.     

Weaning of bullseye puffer (Sphoeroides annulatus) from live food to microparticulate diets made with decapsulated cysts of Artemia and fishmeal

Two experiments were carried out to test microparticulate diets forweaning hatchery-produced larvae and juveniles of bullseye pufferSphoeroides annulatus. The diets were formulated with differentprotein sources: diet 1 with a combination of decapsulated cysts ofArtemia and fishmeal, and diet 2 with a combination offishmeal, squid, tuna gonad and shrimp meal. In the first experiment60-days-old fish were weaned with the microdiets over five days. Fishsurvival after 11 weeks of feeding was 92% for diet 1, 85%for diet 2, and 95% for the control fish fed Artemianauplii. Once it was determined that bullseye puffer can be adequatelyreared with artificial dry diets, diet 1 was used to test earlier timesfor weaning to reduce the period of Artemia feeding. In thesecond experiment, three different times were tested for initiation ofweaning in sibling fish larvae, i.e., at 29, 34, and 39 days post-hatch.Small differences in weight, length and survival were found amongweaning treatments after 23 days of feeding. When weaned at day 29post-hatch, fish larvae grew from an initial weight of 38.4 mg andlength of 11.1 mm to a final weight and length of 405.7 mg and 25.1 mmrespectively. Final survival in this treatment was 49.3%. Thereduced period of Artemia feeding would provide an economicalalternative for the species to take into consideration for its cultureat commercial scale.