Evaluating bioencapsulation of florfenicol in rotifers (Brachionus plicatilis)

The rotifer Brachionus plicatilis is one of the most important live‐feed organisms used in the larval culture of marine fish. Bioencapsulation of florfenicol in rotifers was investigated by delivering it directly to the organisms as particles and the doses ranged from 50 to 1000 mg L^?1. Analysis of the florfenicol concentrations in rotifers was performed using high‐performance liquid chromatography. The uptake increased with the dose and the enrichment time, and the highest concentration achieved in this study, 1.25 ng rotifer^?1, was obtained using a dose of 1000 mg L^?1 and 150 min of enrichment. The optimal time for satisfactory enrichment of rotifers with florfenicol was found to be dose dependent and ranged from 30 to 120 min for doses between 400 and 800 mg L^?1. The parameters affecting the concentrations achieved in rotifers were the size of the florfenicol particles, enrichment time and dose.     

Essential fatty acid enrichment of cultured rotifers (Brachionus plicatilis, Müller) using frozen-concentrated microalgae

There is a growing interest in preserving microalgal preparations to maintain constant properties over a long period. The aim is to ensure sufficient delivery of essential fatty acids (and other key nutrients) to mollusc and crustacean larvae and to zooplankton used as live prey in the first feeding of fish larvae. For example, the rotifer Brachionus plicatilis has to be enriched with polyunsaturated fatty acids (PUFA) prior to fish feeding. We used four microalgal species [ Isochrysis galbana (T-ISO), Chaetoceros muelleri (CHGRA), Pavlova lutheri (MONO), and Nannochloropsis sp.] both as fresh culture or in a frozen-concentrated form to enrich rotifers. Overall, rotifers had similar relative fatty acid levels when fed the frozen-concentrated or fresh microalgal diets. The levels of 20:4n-6, 22:6n-3, and 20:5n-3 between B. plicatilis and the microalgal diets were linearly correlated. The fatty acid 20:4n-6 was the most readily assimilated: the content found in rotifers reached half the level measured in the microalgal diets. Our results indicate that both the fresh and frozen-concentrated forms of the four microalgal species can be used to enrich PUFA levels in rotifers. Further experiments should be conducted to test if assimilation differs when rotifers are enriched with mono- or multispecific microalgal preparations.     

Biochemical and technical observations supporting the use of copepods as live feed organisms in marine larviculture

The use of live prey is still necessary for a large number of raised fish species. Small sized rotifers are usually used as live preys during the first days of feeding in small mouth fish. An alternative to this is the use of copepods as prey for first feeding. In this study, the sizes, weight and biochemical contents of two copepods and one rotifer species raised on similar algal food conditions were compared. Rotifers contained a higher proportion of essential amino acids in the free amino acid (FAA) fraction (43%) than copepods (30–32%). However, rotifers had lower levels of important fatty acids like DHA (7% compared with 23–32% in copepods) and their DHA/EPA ratio was lower than that in copepods (0.54 compared with 1.35–1.63 in copepods). The FAA pattern of the preys tended to be species‐specific and its implications from an aquaculture point of view is discussed. In contrast, the‐protein bound amino acids tended to be very conservative among the studied organisms. The second part of the work is focused on ‘the price’ of hatching in Acartia tonsa eggs before or after cold storage at 3°C. The fatty acid contents in A. tonsa tended to decrease with the storage time. It also decreased with hatching of the nauplii, but its proportion compared with the dry weight remained constant.     

The effect of different HUFA enrichment emulsions on the nutritional value of rotifers (Brachionus plicatilis) fed to larval haddock (Melanogrammus aeglefinus).

A feeding study was conducted in the winter 2001 to determine the effects of feeding rotifers (Brachionus plicatilis) enriched with various levels of essential fatty acids on the growth and survival of haddock larvae (Melanogrammus aeglefinus). Rotifer enrichment treatments were: 1) mixed algae, 2) high DHA (docosahexaenoic acid, 22:6n-3), 3) high DHA and EPA (eicosapentaenoic acid, 20:5n-3), and 4) DHA, EPA, and AA (arachidonic acid, 20:4n-6). Larvae were fed rotifers enriched with the different treatments from days 1 to 16 post-hatch. From day 17 until 25 all treatment groups were fed rotifers reared on mixed algae and then weaned onto the International Council for Exploration of the SEA (ICES) Standard Reference Weaning diet (http://allserv.rug.ac.t/aquaculture/rend/rend.htm) over a five day period. The experiment was terminated on day 41 post-hatch. The enrichment treatments affected the fatty acid composition of the rotifers and correlated with the accumulation of these fatty acids in the haddock larvae. However, no significant differences in larval growth or survival to 40 days post hatch were detected, suggesting that all treatments provided the minimal essential fatty acid requirements for haddock.     

Effects of adult stocking density on egg production and viability in cultures of the calanoid copepod Acartia tonsa (Dana)

The effect of stocking density of the calanoid copepod Acartia tonsa was evaluated in a 96 h rearing experiment. Possible density‐dependent egg production and egg viability were analysed at stocking densities of 100, 200, 300, 400 and 600 adults L⁻¹. Temperature, oxygen saturation and algal concentration were kept optimal. A non‐density‐dependent mortality rate of 15–19% day⁻¹ was documented. A non‐significant density‐dependent egg production was observed between 100 and 600 adults L⁻¹. The average egg production was 22.5±8.8 egg female⁻¹ day⁻¹ in all densities. The average egg hatching success was 84.7±4.8% and was never observed below 76.1%, with no significant differences across the stocking densities. Conclusively, as a practical recommendation for the aquaculture industry, copepod cultures with densities ranging from 100 to 600 adults L⁻¹ and presumably even more dense cultures are possible with the studied species obtaining a steady egg production and still high egg viability.     

Use of a potential probiotic Lactococcus lactis AR21 strain for the enhancement of growth in the rotifer Brachionus plicatilis (Müller)

The effect of a potential probiotic on the growth performance of a rotifer and its inhibition against Vibrio anguillarum was studied. Probiotic strain AR21 had no significant observable effect on the growth rate of rotifers under optimal culture conditions in three consecutive experiments. In the first and second experiments, the AR21 strain exhibited an inhibitory effect against the V, anguillarum strain when rotifer cultures were maintained at a suboptimal feeding regime. The growth rate of the rotifers in suboptimal feeding conditions was significantly higher in the treatment receiving AR21 and V. anguillarum than in the treatment where only V. anguillarum was added.     

Morphometric changes in a strain of the lineage 'Nevada', belonging to the Brachionus plicatilis (Rotifera) complex

The rotifer Brachionus plicatilis is an important component of aquaculture as a larval feed. Its taxonomic status has been recently re-defined as a species complex, consisting of at least 14 new species/lineages. This study deals with the lineage Brachionus 'Nevada', which has been shown to occur in European hatcheries. A strain of B . 'Nevada' was mass cultured using two commonly applied feeding regimes and analysed in terms of its morphometry. A new formula was proposed for the calculation of volume, which can be used as an index of adequacy of rotifers as feed for fish larvae. The results were related to life cycle parameters. The pre-reproductive and reproductive phases were divided into distinct size groups. Differences were also found between the two diets in morphometry and demography. Rotifers of a larger size (yeast-based diet) showed a lower growth rate and a longer reproductive period, lifespan and mean generation time compared with smaller-sized rotifers (Culture Selco^®-based diet). In terms of lorica length, the present study's strain of B . 'Nevada' (238.5 μm) was intermediate between values reported for Brachionus ibericus (193.5 μm) and B. plicatilis sensu stricto (299 μm).     

Salinity-induced quiescence in eggs of the calanoid copepod Acartia tonsa (Dana): a simple method for egg storage

We report the effect of salinity and temperature on the viability of stored culture-based subitaneous eggs of the calanoid copepod Acartia tonsa for use of copepods in fish larvae culture. Quiescence induction was recorded at 17 and 25 °C, in salinities from 0 to 30. Quiescence was strongly induced at 0 salinity and partially at 5 in both temperatures. Eggs incubated at 0 salinity for up to 12 days at both temperatures showed a decline in the fraction able to be induced into quiescence by abrupt salinity changes. The hatching success of eggs that were able to enter quiescence stabilized after a 1-day incubation and remained ∼25% viable for 12 days in 17 °C. On the contrary, the 25 °C trial showed a gradual decline in viability until stabilizing ∼10% at day 7 and onwards. Longterm 17 °C incubation for 35 days showed that eggs remained quiescent with a viability of ∼14%. Hence, we recommend salinity storage of A. tonsa subitaneous eggs as a relevant shortterm technique, and a suitable alternative to the recently proposed cold storage of eggs when eggs are to be shipped from the copepod producer to a given fish larvae hatchery.     

Evaluating the use of Lactobacillus acidophilus as a biocontrol agent against common pathogenic bacteria and the effects on the haematology parameters and histopathology in African catfish Clarias gariepinus juveniles

This study was carried out to evaluate the use of Lactobacillus acidophilus as a biocontrol agent against some common fish pathogenic bacteria (Staphylococcus xylosus, Aeromonas hydrophila gr.2 and Streptococcus agalactiae) in African catfish, Clarias gariepinus. Eight treatments were designed inclusive of 10 C. gariepinus juveniles (mean weight 190 g) per tank, each in triplicate. Four groups of fish were fed a diet supplemented with L. acidophilus, comprising about 3.01 × 10⁷ colony‐forming units per gram of diet (the probiotics diet), while the other four groups were fed a diet not supplemented with probiotics (the non‐probiotics diet). In the first group, fish were injected with 1 mL physiological saline and fed the non‐probiotic diet (non‐probiotic control); in the second, third and fourth groups, fish were injected with 1 mL each of S. xylosus, A. hydrophila gr.2 and S. agalactiae, respectively, and were all fed the non‐probiotic diet (designated as non‐probiotic treatments; NPsx, NPah and NPsa respectively). In the fifth group, fish were injected with 1 mL physiological saline but fed the probiotic diet (probiotic control), while fish in the sixth, seventh and eighth groups were each injected with 1 mL of S. xylosus, A. hydrophila gr.2 and S. agalactiae, respectively, and were all fed the probiotic diet (and designated as probiotic treatments; Psx, Pah and Psa respectively). Blood samples were collected for haematology analysis, while samples of the liver and kidney were examined for pathohistology after 7 and 21 days of infection. The results showed that the haematology parameters, packed cell volume, haemoglobin, erythrocyte sedimentation rate, red blood cell, white blood cell, total serum protein, Mg²⁺, Ca²⁺, Cl^?, glucose, cholesterol and total immunoglobulin concentrations and the pathohistology of the liver and kidney were better in the challenged fish (infected) maintained on the probiotic diet than those in the groups fed the non‐probiotic diet. It is concluded, based on these results, that L. acidophilus is useful as a probiotic agent in C. gariepinus against these pathogenic bacteria (S. xylosus, A. hydrophila gr.2 and S. agalactiae).     

Use of Cyclop-eeze as a substitute for Artemia nauplii in larval rearing of giant freshwater prawn Macrobrachium rosenbergii (De Man 1879)

Four feeding experiments, replacing 25% (T₁), 50% (T₂), 75% (T₃) and 100% (T₄), by dry weight, of the live feed Artemia nauplii for Cyclop‐eeze, a new larval feed that was claimed to contain the highest known levels of astaxanthin and omega‐3 polyunsaturated fatty acids, were compared against a control that was fed with Artemia and egg custard alone, to the larvae of giant freshwater prawn Macrobrachium rosenbergii (De Man 1879). Analysis of different production characteristics of the larvae revealed that the highest survival up to postlarvae (PL) stage was obtained for T₂ in which 50% of the Artemia nauplii were replaced by Cyclop‐eeze [freeze‐dried (FD) deep frozen (DF)], and the highest astaxanthin content of the larval tissue obtained in T₄ in which the larvae were fed 100% Cyclop‐eeze, although the survival rate was the lowest in this treatment. The costs of different treatments were also compared. The Artemia consumption million⁻¹ larvae was the highest in control (11490 g), followed by T₁ (8240 g), T₂ (4990 g), T₃ (3730 g) and T₄, which completely replaced Artemia from stage 5 onwards (1830 g). The highest consumption of Cyclop‐eeze million⁻¹ larvae was in T₄ (1670 and 10 880 g), followed by T₃ (850 and 5560 g), T₂ (410 and 2690 g) and T₁ (230 and 1490 g) of FD and DF, respectively. The astaxanthin contents of the late‐stage larvae fed under the four treatments were 24.90, 27.40, 28.60 and 35.60 μg g⁻¹ tissue for T₁, T₂, T₃ and T₄, respectively, while that of the control was 23.70 μg g⁻¹. The lowest cost of live feeds million⁻¹ PL was obtained for T₂ (US$ 428.60), followed by T₁ (US$ 490.46), control (US$ 529.07) and T₃ (US$ 583.26), while it was the highest for T₄ (US$ 890.93). The results indicated that Cyclop‐eeze could economically replace Artemia nauplii at 50% level that could significantly improve the survival and carotenoid composition of the larvae of M. rosenbergii.     

Suitability of the copepod, Acartia clausi as a live feed for Seabass larvae (Lates calcarifer Bloch): Compared to traditional live-food organisms with special emphasis on the nutritional value

Though artificial propagation of Asian seabass Lates calcarifer (Bloch) in captivity through induced breeding techniques is standardized under Indian conditions, larval and nursery rearing techniques including suitable nursery feeds have to be standardized to obtain better survival and growth. Feeding experiments in triplicate were conducted to evaluate the suitability of the marine copepod Acartia clausi as live prey for fourteen day-old seabass larvae (6.53 ± 0.06 mm; 8.58 ± 0.33 mg) and compared with the traditional live prey, rotifers and Artemia nauplii. While A. clausi and rotifers were mass produced using algae Isochrysis galbana, Chaetoceros affinis and Chlorella marina, Artemia nauplii were produced using cysts. Nutritional quality of cultured copepods was evaluated based on the proximate composition, amino acid and fatty acid composition, and compared with that of rotifers and Artemia nauplii. Proximate composition varied significantly (P < 0.05) among the different live feeds. A. clausi showed higher protein (63.12%) and lipid (16.65%) content than Artemia nauplii and rotifers. Total essential amino acids content was 2% lower in A. clausi compared to that in Artemia nauplii. Fatty acid profiles of the live feed organisms showed that A. clausi is a rich source of n − 3 fatty acids. The total n − 3 fatty acid content of A. clausi was 33.94%. Length, weight overall weight gain and survivorship were significantly (P < 0.05) different among the dietary treatments, and weight gain was comparatively higher in A. clausi fed larvae. Survival of seabass larvae fed A. clausi was obtained highest as 58.13% against the lower values of 39.93% and 41.62% in larvae fed rotifer and Artemia nauplii respectively. Final carcass composition of the larvae of L. calcarifer fed different live-food organisms showed significant differences (P < 0.05) among the dietary treatments. The fatty acid composition of the dietary treatments was reflected to a certain extent in the fatty acid composition of the seabass larvae. The present investigation revealed the nutritional value of calanoid copepod and thus underlining its usefulness as a suitable live-food organism for rearing larvae of the commercially valuable Asian seabass.     

Panagrellus redivivus (Linné) as a live food organism in the early rearing of the catfish Synodontis petricola (Matthes)

The nematode Panagrellus redivivus (Linné) has been suggested as a source of live food in the rearing of larval fish and shrimp species. This study tested the use of P. redivivus in the early rearing of the bottom‐feeding catfish Synodontis petricola (Matthes). A comparison of feeding rates of 5000–10 000 nematodes larva⁻¹ day⁻¹ showed that fish receiving 5000 nematodes larva⁻¹ day⁻¹ grew faster than those fed a dry diet, but slower than treatments fed 200 and 600 Artemia larva⁻¹ day⁻¹. Enrichment of nematodes with SuperSelco^® improved fish growth relative to a non‐enriched control treatment, with both treatments receiving 5000 nematodes larva⁻¹ day⁻¹. In the first two trials, feeding commenced 2 days after hatching. In the third study, fish were fed nematodes 6 days after hatching and there was no difference in growth between Artemia‐fed fish (600 Artemia larva⁻¹ day⁻¹) and fish fed 5000 nematodes larva⁻¹ day⁻¹. Thus, it is suggested to feed S. petricola at a nematode density of at least 10 000nematodes larva⁻¹ day⁻¹ in order to achieve growth comparable to that of fish fed Artemia, or, alternatively, to feed 5000 nematodes larva⁻¹ day⁻¹ to improve growth relative to that achieved with a dry diet. Furthermore, nematodes may be enriched with essential fatty acids to improve the growth of S. petricola larvae.     

Use of biomass of the marine microalga Isochrysis galbana in the nutrition of goldfish (Carassius auratus) larvae as source of protein and vitamins

The effect of the replacement of fish protein hidrolizate and vitamin premix by freeze‐dried biomass of the marine microalga Isochrysis galbana in the feed for goldfish (Carassius auratus) larvae was tested. Larvae (3.4±0.7 mg) were fed with three experimental microparticulated diets that differ from each other in the percentage of replacement of fish protein hidrolizate (25% or 100%) or vitamin premix by I. galbana biomass. The control diet and the diet containing microalgae biomass as a substitute of 25% of fish protein hidrolizate (MP₂₅) presented the highest survival, being almost 100%, with no significant differences between them. Survival in diets in which 100% of fish protein hidrolizate (MP₁₀₀) or vitamin premix (MV) had been substituted by microalgal biomass was 78% and 66% respectively. Growth, measured as weight, was lower than with the control diet in all treatments in which microalgal biomass was included, with lowest results being obtained with the MP₁₀₀ diet. Differences between treatments and control were lower when growth was measured as length. The harvesting and processing microalgae biomass is crucial to maintain the nutritive value and could be the cause for the obtained results.     

Biofouling as a reservoir of Neoparamoeba pemaquidensis (Page, 1970), the causative agent of amoebic gill disease in Atlantic salmon

Amoebic gill disease (AGD) is currently the most important disease affecting the Tasmanian salmonid industry and is caused by a marine amoeba, Neoparameoba pemaquidensis (Page, 1970). In this study biofouling communities on salmon cages were surveyed for the presence of the disease agent over a period of 4 months. Malt–yeast–seawater (MYS) agar plates were used to culture N. pemaquidensis with its presence confirmed by immunofluorescent antibody test (IFAT). Positive percentages of categorised samples ranged from 0% to 55%. The survey detected the presence of N. pemaquidensis on a number of macrofouling species (in particular bryozoan Scrupocellaria bertholetti and solitary ascidian Ciona intestinalis), and in microfouling and water samples. High percentages of positive IFATs occurred in microfouling aggregates, the solitary ascidian, C. intestinalis, and centrifuged water samples. No positive IFATs occurred from samples of Caprella sp. The presence of N. pemaquidensis was sporadic and varied in species and over sampling month. Experimental exposure of Atlantic salmon, Salmo salar, to lightly fouled netting was conducted to assess the potential for microfouling to act as a source of infection. No signs of the disease were detected in fish exposed to lightly fouled netting treatments, while 100% of positive control fish were infected and had an average of 4.24±1.79 amoebae per field of view in IFAT of mucus smears. When combined with N. pemaquidensis loads in the water column, the loads of amoebae in biofouling communities may contribute to disease outbreaks. Thus, biofouling should be considered a risk factor for AGD outbreaks.     

Preliminary evaluation of the seaweed Gracilaria cervicornis (Rhodophyta) as a partial substitute for the industrial feeds used in shrimp (Litopenaeus vannamei) farming

The aim of this study was to evaluate the use of Gracilaria cervicornis meal as a partial substitute for the industrial feeds used in shrimp (Litopenaeus vannamei) farming. A total of 90 L. vannamei juveniles (0.34 g) were assigned randomly into nine experimental units at a stocking density of 10 shrimp tank⁻¹ and fed a commercial shrimp feed (CSF; 35% crude protein) as a control treatment, a feed made entirely of G. cervicornis (GCM), and a mixture of equal parts of the commercial shrimp feed and the Gracilaria meal (MIX) for 30 days. Over the first 2 weeks of the experiment, the survival was high (100%) in all dietary treatments. However, at the termination of the feeding trial survival decreased to 40% in shrimp fed GCM, significantly lower (P<0.05) than survival of shrimp fed the commercial diet control (CSF) or MIX treatments (100%). The highest growth performance was obtained in the CSF or MIX treatment groups. The absolute growth increase in these groups was significantly higher than for shrimp fed GCM. Similarly, the specific growth rates (SGRs) of shrimp given feeds containing CSF (5.11% day⁻¹) and MIX (4.71% day⁻¹) were significantly greater (P<0.05) than that of shrimp fed GCM pellets (0.44% day⁻¹). The feed efficiency ratios (FERs) were 64 for CSF, 54.3 for MIX and 3.3 for GCM. The results obtained in this study indicated the effectiveness of using G. cervicornis as a partial substitute for shrimp feeds. To our knowledge, this is the first time that the concept that macroalgae can partially substitute for the industrial feeds used in shrimp (L. vannamei) farming has been demonstrated.     

Evaluation of flocculated concentrates from intensive shrimp pond water as a substitute for microalgal concentrates in the nursery culture of juvenile oyster (<Emphasis Type="Italic">Crassostrea belcheri</Emphasis>)

Intensive shrimp pond water typically contains high densities of microalgae and may have a great potential as a substitute for microalgae in the nursery culture of juvenile oysters as this stage needs large amount of microalgae. Two experiments with different phytoplankton composition in flocculated concentrates from shrimp pond water were investigated to compare the effect on preservation and use of flocculated concentrates from intensive shrimp pond as a partial substitute for microalgae concentrates for the nursery culture of juvenile oysters (Crassostrea belcheri) was evaluated. The results show that total crude protein content in flocculated concentrates mostly contain unidentified nanocyanobacteria preserved in refrigerator at 4 °C gradually decreased from the first week in experiment 1, while a slight decrease in crude protein content appeared after the third week in flocculated concentrates dominated by the Bacillariophyceae and unidentified nanocyanobacteria groups in experiment 2. The pheophytin a:chlorophyll a ratio suddenly increased during the third week of storage and most of the fatty acid composition was absent after four weeks of storage in both experiments. Substituting 75 % of microalgal concentrates in feed with flocculated concentrates from shrimp pond water showed no significant differences in growth performance in experiment 1, but higher growth performance in experiment 2 in comparison with control treatment (100 % microalgal concentrates). Our findings indicate that a partial substitution of flocculated concentrates of up to 75 % from shrimp pond water for microalgal concentrates would lead to better growth in juvenile oysters.     

Study on the distribution and expression of a DNA vaccine against lymphocystis disease virus in Japanese flounder (Paralichthys olivaceus)

The distribution and expression of lymphocystis disease virus (LCDV) vaccine, on the basis of DNA vaccine (pEGFP-N2-LCDV0.6 kb) construction, were analyzed in tissues of the Japanese flounder by PCR, RT-PCR and fluorescent microscopy. Results from PCR studies indicated that the vaccine-containing plasmids were distributed in injected muscle, muscle located opposite the injection site, hind intestine, gill, spleen, head kidney, liver and gonad 7 days after vaccination. However, these vaccine-containing plasmids disappeared by 90 days following vaccination. Fluorescent microscopy observations revealed that green fluorescence appeared in muscle, muscle located at the opposite side of the injection site, hind intestine, gill, spleen, head kidney and liver of fish 36 h after vaccination, and that green fluorescence did not appear in control tissue. The green fluorescence became weaker at 60 days post-vaccination, however, it remained detectable in the spleen 90 days post-vaccination. Results from RT-PCR studies indicated that the Mcp gene is expressed in all tissues of vaccinated fish 7-20 days after vaccination. These results demonstrate that the DNA vaccine is distributed and expressed in different tissues of vaccinated fish, and therefore, may have provided an antigen producing specific immune response.     

An analysis of refractometry as a method of determining blood total protein concentration in the American lobster Homarus americanus (Milne Edwards)

Given the high unit value of live American lobsters (Homarus americanus), a non‐destructive field method to assess physiological state is desirable during out‐of‐water transport conditions. This study compared an Uricon® specific gravity refractometer, with a commercial veterinary blood analyser (Vet‐Test), as a method for determining the blood total protein concentration in live, out‐of‐water individuals. Regression analysis of R² = 0.8641 (n = 64) was observed in determination of blood total protein concentration, y = 0.0036x + 1.0163 where x is the protein concentration in mg dL^?1 in Vet‐Test. Our results (R² = 0.864, SE ± 0.003) support the results (R² = 0.985) of the previous study conducted by Leavitt & Bayer (1977 ) in which serum total protein was compared with the refractometric method. We therefore confirm that the refractometric method can be used as a reliable method to indicate health of a lobster by measuring the blood total protein concentration. The results show good correlation between the protein concentrations observed using the refractometric method and a Vet‐Test blood chemistry analyser. anova analysis was significant between the protein refractometer and the Vet‐Test (P < 0.05). Although protein concentration units obtained from both methods were different the results followed the same trends. Refractometry as a method is reliable to determine blood total protein concentrations in the American lobster. Consequently, a refractometric method can be used directly by commercial growers and distributors to assess responses to holding facility conditions and to feeding regimes. Whole blood protein concentrations may provide more information than serum protein concentrations as measured in the study of Leavitt & Bayer (1977 ).     

Quantification of vitellin/vitellogenin-like proteins in the oyster Crassostrea corteziensis (Hertlein 1951) as a tool to predict the degree of gonad maturity

The oyster's reproductive process is poorly documented, especially in terms of a quantitative approach. In recent years, investigations with this species have been directed at determining important reproductive factors. Within this scope, techniques that allow standardized and accurate quantitative estimations of gonad development have become of primary importance. In this study, the histological characteristics and the levels of vitellin/vitellogenin-like proteins (Vn/Vtg) from ovaries of the Mexican Pacific 'pleasure' oyster Crassostrea corteziensis (Hertlein 1951) were analysed during different stages of gonad maturation using quantitative histological techniques and an enzyme-linked immunosorbent assay. This was performed in order to evaluate a possible quantitative tool to predict the degrees of gonad maturity and to analyse the biological implications of the findings relative not only to broodstock conditioning but also to natural populations. Using this information, we expect to be able to undertake further research on different reproductive aspects of this oyster species, including, among others, evaluation of the response in Vn/Vtg concentrations to different diets and environmental conditions during laboratory conditioning.     

Potential of the use of peanut (Arachis hypogaea) leaf meal as a partial replacement for fish meal in diets for Nile tilapia (Oreochromis niloticus L.)

The rapid growth of tilapia culture has stimulated the expansion of tilapia feed production and a search for novel protein sources to replace fish meal. Vegetable or plant sources are promising alternatives and legumes are both naturally abundant and high in protein content. A study was carried out to evaluate the effects of replacing the protein from fish meal with peanut ( Arachis hypogaea ) leaf meal (PLM) in diets for male tilapia ( Oreochromis niloticus , initial body weight 75.3 g). Four isonitrogenous (35% CP) and isocaloric (18.834 kJ g⁻¹) diets were prepared to include 0% (CON), 10% (PLM10), 20% (PLM20) and 30% (PLM30) of PLM protein. Average fish weights at the end of the 126-day experiment were not statistically different among the fish fed CON, PLM10 and PLM20 diets. The PLM30 diet produced the poorest growth performance. Organic matter and protein contents of fish were similar in the CON, PLM10 and PLM20 diets. Carcass chemical composition showed a decrease in body fat content as PLM replacement levels increased. The high survival ratio in all dietary groups (>97%) suggests that PLM can be used in O. niloticus feeds for long periods without affecting fish growth performance or health.