Juvenile Diet Research Articles

Diet and Food Choice in Peruvian Red Uakaris (Cacajao calvus ucayalii): Selective or Opportunistic Seed Predation?

Even primates considered dietary specialists tend to eat a combination of fruit pulp, seeds, other plant parts, or animals. Specialist seed predators could either feed on seeds preferentially, or to avoid competition when ripe pulps are scarce. Pitheciin monkeys have specialized dentition that allows them to feed on seeds protected by hard shells, and the upper limit on the hardness of these is likely to be a function of jaw size. We recorded the diet of Peruvian red uakaris (Cacajao calvus ucayalii) on the Yavari River, Peru, to test the prediction that this seed predator would feed on the seeds of hard-shelled fruits preferentially over softer ones in relation to their availability in the forest. We also tested predictions that adult male, adult female, and juvenile diets would differ, with larger individuals eating more hard fruits. Uakaris ate 55.4% seeds, 38.9% pulps and arils, and 5.6% other items, but proportions varied through the year. More pulps, especially from the palm Mauritia flexuosa, were eaten when fruit availability was low, and more hard fruits were positively selected for than softer ones. Juveniles did not open the hardest fruit species opened by adults, and adult males ate harder fruits than females. These results provide evidence that seed eating in some primates has evolved beyond a means of avoiding competition for the ripe pulps typically preferred by many primates. Specialist seeding-eating primates therefore occupy divergent niches that require separate consideration from those of similar-sized primates.

Feeding ecology and trophic level of the banded guitarfish, Zapteryx exasperata, inferred from stable isotopes and stomach contents analysis

The feeding ecology and trophic level of the banded guitarfish, Zapteryx exasperata, from the Gulf of California, were assessed using stable isotope analysis (SIA) of carbon and nitrogen in muscle samples, and stomach contents analysis (SCA). Males and females showed similar diet preferences with a high diet overlap (Cλ = 0.99) and similar values of δ13C and δ15N (ANOVA, F = 0.0 p = 0.94 for δ13C; F = 0.1 p = 0.78 for δ15N). The main prey groups found were demersal fishes dominated by the daisy midshipman, Porichthys margaritatus, (>90%IRI), however, pelagic fishes were also found (Engraulis mordax 2%IRI). An ontogenetic diet shift was found, indicated by the importance of crustaceans in the juvenile diet and the significant isotopic differences between juveniles and adults (δ13C, ANOVA, F = 13.3 p = 0.0004 and δ15N, ANOVA, F = 4.7 p = 0.03). An overall trend of increase in δ15N values with increasing body length (F = 8.15 p = 0.005) was observed. The mean trophic level estimated in this work by the two methods was ~4.1, indicating that this species is a top predator in the Gulf of California. Zapteryx exasperata is a specialist feeder (Bi = 0.11, H’ = 2.32), consuming mainly benthic fishes in coastal areas of the Gulf of California. The importance of this species in the benthic ecosystem equilibrium as a top predator is an important point to keep in mind when developing future management plans of the batoid fishery in the Gulf of California.

Biology and invasive potential of the introduced swordtail Xiphophorus hellerii Heckel (Poeciliidae) in Western Australia

Abstract The swordtail Xiphophorus hellerii is a popular ornamental freshwater fish that occurs as an introduced species in the aquatic habitats of at least 31 countries. Although introduced populations are found in other Australian states, the only known Western Australian population occurs in the Irwin River (29°15′S). The biology of X. hellerii in the Irwin River in south‐western Australia is described from four seasonal samples, collected by seine net, between spring 2002 and winter 2003. Pregnant females were collected in all seasonal samples, though juveniles were absent in spring, implying that juvenile mortality during late winter is high. Although mean length of pregnant females (38.7 mm) and mean gonadosomatic index (GSI) (14.7) were similar to reported data for X. hellerii populations in Queensland, mean fecundity was markedly lower in Western Australia, i.e. 34.1, cf. 60.15. Logistic analysis of the percentage of female and male X. hellerii with developing and mature gonads predicted that the length at which 50% of the sexes mature was 30.8 and 31.5 mm SL, respectively. The sex ratios of females to males did not differ statistically from a ratio of 2:1. The diet of all X. hellerii size classes was omnivorous (primarily vegetal matter/algae), although a significant difference was observed between the diet of juveniles and that of the two larger size classes (i.e. juveniles consumed greater quantities of aquatic invertebrates). A melanic polymorphism (i.e. pigmented caudal peduncle and fin) was observed in approximately 5% of X. hellerii collected. If released, the range of X. hellerii is likely to expand in anthropogenically modified habitats in tropical and temperate latitudes of Western Australia. Potential ecological impacts on indigenous fishes may be magnified owing to the depauperate nature of the endemic ichthyofauna including a lack of predators. Copyright © 2011 John Wiley & Sons, Ltd.

Diet of juvenile southern elephant seals reappraised by stable isotopes in whiskers

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 424:247-258 (2011) - DOI: https://doi.org/10.3354/meps08769 Diet of juvenile southern elephant seals reappraised by stable isotopes in whiskers China Newland1,*, Iain C. Field1,2, Yves Cherel3, Christophe Guinet3, Corey J. A. Bradshaw4,5, Clive R. McMahon1,6, Mark A. Hindell1 1Antarctic Wildlife Research Unit, School of Zoology, University of Tasmania, PO Box 252-05, Hobart, TAS 7001, Australia 2Marine Mammal Research Group, Graduate School of the Environment, Macquarie University, Sydney, NSW 2109, Australia 3Centre d’Etudes Biologiques de Chizé, UPR 1934 du CNRS, BP 14, 79360 Villiers-en-Bois, France 4The Environment Institute and School of Earth and Environmental Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia 5South Australian Research and Development Institute, PO Box 120, Henley Beach, South Australia 5022, Australia 6School for Environmental Research, Charles Darwin University, Casuarina Campus, Darwin, Northern Territory 0909, Australia *Email: cnewland@utas.edu.au ABSTRACT: Declines in marine predator populations have been attributed to anthropogenic activity and environmental change. Southern elephant seals Mirounga leonina are major consumers of biomass in the eastern region of the Southern Ocean and have been declining in numbers since the 1960s. Previous studies have identified evidence for habitat and diet partitioning over a range of spatial and temporal scales between juveniles and adults in the Macquarie Island population. We first analysed the stable isotopes (SI) of 6 entire vibrissae from a dead adult female southern elephant seal from Kerguelen Islands to determine moult and growth patterns. Secondly we analysed the SI from the vibrissae of 102 juvenile southern elephant seals to investigate diet. The results from the growth pattern analysis indicated that vibrissae do not grow or moult simultaneously. However, it is likely that at least part of the vibrissae will have been produced sometime during the most recent trip to sea and will give a broad indication of diet. The subsequent SI analysis confirmed that juveniles are consuming greater proportions of fish species, and identified myctophids as the primary component of juvenile diet. Myctophids are also consumed by king penguins Aptenodytes patagonicus which have greatly increased in numbers recently in the Macquarie Island area. This may have presented the juvenile southern elephant seals with increased competition and may influence survival. KEY WORDS: Stable isotopes · Vibrissae growth patterns · Diet · Fish · Squid · Resource partitioning · Inter-specific competition Full text in pdf format PreviousNextCite this article as: Newland C, Field IC, Cherel Y, Guinet C, Bradshaw CJA, McMahon CR, Hindell MA (2011) Diet of juvenile southern elephant seals reappraised by stable isotopes in whiskers. Mar Ecol Prog Ser 424:247-258. https://doi.org/10.3354/meps08769 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 424. Online publication date: March 01, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

The Effect of Partial Replacement of Dietary Fishmeal with Fermented Prawn Waste Liquor on Juvenile Sea Bass Growth

A feeding trial was conducted for 49 days to evaluate the effect of partially substituting fishmeal with fermented prawn waste liquor (FPWL) in juvenile sea bass diets at 10%, 20%, and 30% of the total diet. Growth performance of sea bass from 16 g up to 40 g fed with FPWL-supplemented diet was not significantly different from the all fishmeal control diet. The most cost-effective diet included FPWL at 30%, with weight gain, feed conversion ratio, and protein efficiency ratio of 180%, 1.78%, and 1.2% respectively.

Lipid composition of the Antarctic fish Pleuragramma antarcticum. Influence of age class

Larvae and juvenile stages of Pleuragramma antarcticum have been collected in the Dumont D’Urville Sea (East Antarctica) during summer 2008 on board the TRV Umitaka Maru during the CEAMARC survey. Detailed analyses of their lipid class and fatty acid compositions were carried out. P. antarcticum showed a pronounced ontogenic lipid accumulation with increasing size. Larvae displayed a dominance of polar lipids (83% of total lipids) and low percentage of triglycerides (7%). Conversely juveniles showed an increasing accumulation of triglycerides (up to 72.4%). The fatty acid composition of polar lipids remained rather stable between stages with 22:6n−3 and 20:5n−3 as dominant contributors. The relatively minor ontogenic changes, e.g. increase of monounsaturated and decrease of C18 polyunsaturated fatty acids, may reflect the influence of differences in diet. Triglycerides showed that all three age classes are well segregated in term of fatty acid composition. Larvae triglycerides are characterized by significant percentages of 16:0, 20:5n−3, 20:6n−3 and to a minor extent 18:4n−3, which suggest a prymnesiophyte based diet. Juveniles are characterized by larger percentages of C20:1 and C22:1 acids, considered as markers of Calanus type copepods. The increasing contribution of 18:1n−9 in the triglycerides of the older juveniles suggests a gradual and increasing shift from a copepod dominant diet to an euphausiid dominant diet. Fatty acid trophic markers pattern suggests a shift from a phytophagous and omnivorous diet for larvae to a carnivorous diet for juveniles.

UTILIZATION OF CORN GLUTEN MEAL AS A PROTEIN SOURCE IN DIETS FOR GILTHEAD SEA BREAM (Sparus aurata L.) JUVENILES

The utilization of corn gluten meal (CGM) was evaluated as a partial fish meal (FM) substitute in practical diets for gilthead sea bream juveniles. Four test diets (isonitrogenous and isoca-loric, 52% protein and 10% lipid, 19 kJ/g diet) containing increasing levels of CGM were for-mulated to replace anchovy meal at levels of 0%, 10%, 20%, and 30%. Triplicate groups of ju-venile sea bream (initial body weight of 1.5 g) were reared in a Recirculating Aquaculture System (RAS) over 45 days at 18±2°C. Fish fed a diet containing 10% of CGM showed com-parable growth performance similar to the control diet containing FM as the sole protein source. No mortality was observed in all treatment groups. Dietary CGM inclusion levels of 20% and 30% showed lower growth performance, feed utilization, and protein efficiency com-pared to the control and the 10% CGM inclusion diets. However these values were not signifi-cantly different among fish fed the CGM10 and CGM20 diets. Economical analyses also con-firmed the growth related experimental results in terms of best profit obtained with the 10% CGM inclusion diet. Results in the present study showed that CGM alone without any amino acid supplements can substitute FM up to 10% with no adverse effects on growth performance, feed utilization, or economical inputs in gilthead sea bream juveniles.

Condition dependence of male display coloration in a jumping spider (Habronattus pyrrithrix)

In many animals, conspicuous coloration functions as a quality signal. Indicator models predict that such colors should be variable and condition dependent. In Habronattus pyrrithrix jumping spiders, females are inconspicuously colored, while males display brilliant red faces, green legs, and white pedipalps during courtship. We tested the predictions of the indicator model in a field study and found that male body condition was positively correlated with the size, hue, and red chroma of a male’s facial patch and negatively correlated with the brightness of his green legs. These traits were more condition dependent than non-display colors. We then tested a dietary mechanism for condition dependence using two experiments. To understand how juvenile diet affects the development of coloration, we reared juvenile spiders on high- and low-quality diets and measured coloration at maturity. To understand how adult diet affects the maintenance of coloration, we fed wild-caught adults with high- or low-quality diets and compared their coloration after 45 days. In the first experiment, males fed high-quality diet had redder faces, suggesting that condition dependence is mediated by juvenile diet. In the second experiment, red coloration did not differ between treatments, suggesting that adult diet is not important for maintaining the color after it is produced at maturity. Diet had no effect on green coloration in either experiment. Our results show different degrees of condition dependence for male display colors. Because red is dependent on juvenile diet, it may signal health or foraging ability. We discuss evidence that green coloration is age dependent and alternatives to indicator models for colorful displays in jumping spiders.

Sexual dimorphism in development and venom production of the insular threatened pit viper Bothrops insularis (Serpentes: Viperidae) of Queimada Grande Island, Brazil

Bothrops insularis is a threatened snake endemic to Queimada Grande Island, southern coast of São Paulo, Brazil, and the occurrence of sexual abnormalities in females (females with functional ovaries and rudimentary hemipenis) has been reported in this population. To date there are few data regarding developmental features of this particular species. The aim of this study was to follow some developmental features in specimens maintained in captivity for seven years in the Herpetology Laboratory at Instituto Butantan, São Paulo, Brazil. We verified a pronounced sexual dimorphism in development and venom production in the specimens analyzed. In this regard, females showed greater length, mass and amount of venom in comparison to males. Our results suggest a possible niche partitioning between the sexes that reduces (or minimizes) intraspecific disharmonic interactions (eg. competition) on their small living area (Queimada Grande Island). Taken together, our data suggest that males and females probably are divergent in their diets, with females feeding preferentially on endothermic prey (such as migratory birds), while males maintain the juvenile diet (with the major items being ectothermic prey).

Alimentação de juvenis de carpa capim com dietas à base de farelos vegetais e forragem

To evaluate the potential of plant-protein sources to replace porcine meat meal in diets for grass carp juveniles, 180 fish (15 per tank) were reared for 60 days in a re-use water system. We evaluated the replacement of porcine meat meal (FCS) for canola meal (FC), sunflower meal (FG) or a mixture of canola and sunflower meal (FCG). The diets were also composed of soybean meal as a protein source. Daily forage intake ranged from 1.24 to 2.11% body weight and did not differ among treatments. Final weight, weight gain, specific growth rate and feed conversion rate did not differ statistically among diets. The fillet yield was higher in FC and FCG diets, while the digestive-somatic index was higher in treatments FG and FCG. Higher fat, lower protein content in whole fish and ash in fillet were obtained in the treatment FCG. The FCG and FCS fillets showed higher L value (brightness). Fish fed the FCS diet had higher values of protein, triglycerides and total cholesterol in serum. We conclude that canola meal and sunflower meal can be used in diets for grass carp in the growing phase.

Studies on impact of the alien Red King Crab (Paralithodes camtschaticus) on the shallow water benthic communities of the Barents Sea

Summary The red king crab Paralithodes camtschaticus (Tilesius, 1815) was introduced in the Barents Sea from the North Pacific in 1961–1969 to establish a fishery. Currently the crab inhabits an area from Kolguyev Island in the east to Soroya in the west, and the total number of adults exceeds 40 million. The crab is a large generalist predator, so its potential impact on native bottom communities is expected to be high. The goal of this study was to review our publications related to the possible impact of the red king crab on the shallow water benthic communities of the Kola Peninsula inlets. First, we reviewed field and experimental data on feeding ecology of different size groups of the crab. Secondly, we examined the data on the benthic communities’ structure in the bays. Finally, assess possible changes in the community structure caused by the red king crab predation. The crab diet includes about 100 species of invertebrates, algae, and fish remnants. Diet of juveniles varied in three studied areas, but bivalve and gastropod mollusks dominated. Experiments on the juvenile feeding showed their positive selection for ophiuroids. Caught prey was usually not completely consumed. Food losses decreased from 50 to 60% in crabs with 35–40 mm carapace width (CW) to 25% in crabs with 70–80 mm CW. Within and between bays trends in the benthic community structure related to the crab density were revealed. Generally, proportion of the stations with disturbed community structure decreased eastward from 80% in the Kola Bay to 18% in the Dolgaja Bay and it was negligible in the Dal’nezelenzkaja Bay. This pattern coincides with the juvenile crab density decreasing eastward. On a smaller scale in the Kola Bay we observed a negative correlation between biomass of macrozoobenthos and juvenile crab density, which was likely related to the crab predation. Comparison of the new data obtained in 2006 with the detailed survey of soft bottom macrobenthos conducted in 1990 in Dolgaja Bay showed a decrease of the diversity of soft bottom communities as well as in species richness, density and biomass of bivalves. Our data demonstrate that the proposed impact of the crab on the bottom communities of the Barents Sea is not as dramatic as have been expected from its high feeding activity and wide diet. We hypothesize that the crab omnivory distributes its predation pressure among various groups of organisms and prevents elimination of particular species or taxa.

Evaluation of zinc supplementation in European sea bass (Dicentrarchus labrax) juvenile diets

This study aimed to investigate the effect of increased zinc dietary levels on the growth performance, feed utilization, immune status and induced wound healing in European sea bass (Dicentrarchus labrax). Fish weighing 10 g were fed five diets containing organic zinc at 30, 70, 110 and 150 mg kg−1 diet and one inorganic zinc source (zinc oxide) at 150 mg kg−1 diet for a period of 12 weeks. No significant (P>0.05) differences were found in the growth performance parameters (final weight, specific growth rate), immunological indices tested (respiratory burst activity in whole blood) and the wound-healing process. Zinc accumulation in the skin, vertebrae and liver increased significantly (P<0.01) with increased dietary zinc levels but not in muscle. The highest zinc concentrations were obtained in skin tissue, followed by vertebrae, liver and muscle tissue. Using the concentration of zinc in skin as a response criterion, broken-line analysis showed that the supplementation of 148 mg organic Zn kg−1 diet seemed to be the optimum dietary zinc supplementation level for sea bass juveniles.

Lipid dynamics during early development of Hippocampus guttulatus seahorses: Searching for clues on fatty acid requirements

The biochemical composition of eggs and the nutrient dynamics during early ontogeny can provide better understanding on the nutritional requirements of both broodstock and first-feeding fish, thus constituting a valuable tool for improvement of aquaculture procedures. This study constitutes the first record of lipid composition and fatty acid dynamics during early development of seahorses. Lipid content and fatty acid profile were determined for Hippocampus guttulatus eggs and newborn juveniles, and their patterns of consumption were analyzed during embryonic development. H. guttulatus produced small broods (426 ± 128 juveniles) but invested in the production of large eggs (2.44 ± 0.37 mm) that resulted in large fingerlings (15.53 ± 1.28 mm), which may have a high survival capacity. The total lipid content of seahorse eggs (17.6% DW) was within the typical range of marine fish eggs. Eggs were dominated by PUFA (43.9%), mainly n−3 HUFA (17.4% of DHA and 13.2% of EPA), and showed a lower MUFA content (22.5%). Extremely low AA levels (0.6%) and particularly high EPA concentrations resulted in a low DHA:EPA ratio (1.3) and high EPA:AA (22.3) and n−3:n−6 (12.2) ratios. Fatty acid consumption during embryonic development was considerably high (67.8%), reflecting the high requirements of seahorse embryos. Fatty acids were depleted at different rates, with PUFA being preferentially consumed (75.2%), while SFA were selectively retained (59.2%). PUFA constituted the major source of metabolic energy and the fatty acids 16:0, EPA and DHA were the main fatty acids to fulfill the energetic demands of seahorse embryos. Essential fatty acids (AA, EPA and DHA) were not preferentially retained, with EPA being catabolized at a particularly high rate (88.0%). These patterns of embryonic consumption resulted in newborn juveniles with an exceptionally low lipid content (5.0% DW), a predominance of SFA (41.0%) and extremely low EPA levels (5.0%). Fatty acid composition of H. guttulatus eggs and juveniles provided important clues to determine seahorse requirements, so that suitable feeding protocols could be developed. The use of broodstock and juvenile diets that reflect the lipid profile of eggs will allow the accomplishment of nutritional requirements and improvement of seahorse production.

Mananoligossacarídeo em dietas para juvenis de tilápias do Nilo

This study was carried out to assess the inclusion of mannanoligosaccharides (MOS) in diets for Nile tilapia juveniles. Two-hundred and twenty fish with an average initial weight of approximately 25 &plusmn; 1.0 g were used, during 53 days. Fish were distributed in a randomized block design. Each 1,000 L tank with four cages (0.12 m3 each), was considered as a block; fish in each cage received a different dietary treatment. A control diet with 28.5% of crude protein and 2,855 kcal of digestible energy kg-1 was used and dietary MOS was included at 0, 1, 2 and 3%. No effects of MOS on feed intake, hepatosomatic index, survival, moisture, body ash, apparent digestibility coefficients of dry matter, gross energy, crude protein, ether extract and ash availability, intestinal villi density and number of goblet cells per villus were observed. The best values of feed-to-gain ratio, protein efficiency ratio, body composition and villi height were observed in fish fed with dietary MOS. It was concluded that 1% of dietary MOS is adequate for Nile tilapia juveniles.

First record of the silver porgy ( Diplodus argenteus) cleaning green turtles ( Chelonia mydas) in the south-west Atlantic

The silver porgy (Diplodus argenteus) of the Sparidae is an occasional cleaner of two species of fish in the south-west Atlantic (Sazima, 1986; Krajewski, 2007). In a recent overview of fish that clean sea turtles (Sazima et al., 2010), 18 reef fish species in seven families are recorded as cleaners/grazers of epibionts of three turtle species of the Cheloniidae. Nine of these fish species (50%) are recorded for the south-west Atlantic (Sazima et al., 2010). The only sparid recorded associated with sea turtles is the sheepshead bream (Diplodus puntazzo), cleaning the loggerhead turtle (Caretta caretta) in the Mediterranean Sea off Greece (Schofield et al., 2006). We record herein for the first time a sparid (Diplodus argenteus) associating with green turtles (Chelonia mydas) and cleaning their carapaces in the south-west Atlantic. Field work was conducted at the rocky shores of Arvoredo Island (about 27817′S 48818′W), off Santa Catarina, southern Brazil. From 2004 to 2008, 334 SCUBA and snorkelling dives (227 hours) at depths 0.5–17 m were conducted in bays of Arvoredo Island, totaling 23 hours of direct underwater observation of turtle behaviour. Ad libitum and ‘behaviour’ samplings (Martin & Bateson, 1986) of general behaviours of focal animals were recorded in sessions that lasted 1–30 minutes. When a cleaning behaviour was sighted, both the turtle and the fish had their sizes estimated (curved carapace length (CCL) and total length (TL), respectively). One cleaned turtle was caught after a cleaning session to collect a sample of epibionts from the spot where the fish were feeding. Only immature individuals of the green turtle were recorded at the shores of Arvoredo Island, which seem to present a degree of residency at this protected area (Reisser et al., 2008). Silver porgy (Diplodus argenteus) juveniles 3–4 cm TL were observed repeatedly biting at the carapaces of green turtles (Chelonia mydas) 30–60 cm CCL on five occasions. One to two juvenile fish individuals feeding on the same turtle were recorded (Figure 1). The cleaned turtle was either swimming slowly in the water column (N 1⁄4 2) or hovering while feeding on red algae (Pterocladiella capillacea) belts on rocky reefs (N 1⁄4 3). The epibionts scraped from the green turtle were mostly Cyanobacteria (blue green ‘algae’) of the Chroococalles, both colonial (63.1%) and unicellular (27.6%), and Oscillatoriales including Lyngbya sp. (4.6%). Chlorophyta (green algae) comprised 3.7%, and the remaining microorganisms found on the carapace were Bacillariophyta (diatoms, 0.7%), and Ciliophora, Vorticellidae (ciliates, 0.2%). Juvenile porgies are omnivores that feed on benthic invertebrates, seaweeds, and zooplankton (Sazima, 1986; Carvalho-Filho, 1999), and most likely benthic microorganisms and epibionts such as those listed above are part of the diet of the small juveniles we recorded cleaning green turtles. Our findings are consistent with a study of the diet of the silver porgy in the same general area we conducted our observations (Dubiaski-Silva & Masunari, 2004). Juvenile silver porgies are able to change their cleaning stations while servicing fish (Krajewski, 2007), which is consistent with our observations of sea turtle cleaning. Our records, although admittedly few (N 1⁄4 5) demonstrate that juvenile porgies are able to move along with slowly swimming turtles, and that they join green turtles at their feeding grounds. Reef fish cleaning sea turtles has been claimed to be a localized phenomenon, restricted to particular populations and/or individuals (Losey et al., 1994). However, data from literature and the present study indicate that reef fish that graze on, clean, or use sea turtles as feeding grounds otherwise, are more common than the available records would indicate (Sazima et al., 2010). Corresponding author: I. Sazima Email: isazima@gmail.com

An investigation into the food and feeding ecology of a potential aquaculture candidate, Sarotherodon galilaeus multifasciatus in a meteoritic crater lake in Ghana

An investigation into the food and feeding ecology of the cichlid, Sarotherodon galilaeus multifasciatus in a tropical meteoritic lake in Ghana was undertaken. Stomachs of the fishes, at two length classes, representing adults and juveniles, were examined and the food items identified. The juveniles of Sarotherodon galilaeus multifasciatus feed mainly on insect and insect larvae and relatively small quantities of diatoms but avoiding macrophytes. A striking feature in the composition of juvenile diet was the considerable quantities of ingested sand, which constituted about 16% of stomach contents. Ingested sand may be helpful in maceration of food in the pyloric stomach. A sandy substratum may, therefore, appear ecologically important for juveniles of the species. Adult stomachs contained mainly phytoplankton, chironomid and insect larvae with no ingested sand. No significant differences were found in the stomach contents of the fishes for the dry and wet seasons due, partly, to the lack of any considerable seasonal differences in allochthonous inputs into the lake waters. The fishes exploit a wide range of food resources in the open, sub-littoral and littoral zones of the lake. Further studies to include growth and recruitment are recommended to enhance future production of the species under culture conditions .

Desempenho e morfometria intestinal de juvenis de tilápia-do-nilo alimentados com dietas suplementadas com L-glutamina e L-glutamato

Este estudo foi realizado para avaliar níveis de L-glutamina e L-glutamato em dietas para juvenis de tilápia-do-nilo (0,60 ± 0,1 g). Foi utilizado delineamento inteiramente casualizado com quatro dietas e três repetições e 90 peixes por unidade experimental. Foi utilizada dieta controle, com 29% de proteína digestível e 2.940 kcal/kg de energia digestível, suplementada mistura de L-glutamina e L-glutamato na proporção de 0, 1, 2 e 3% da dieta, durante 85 dias. Não foi observado efeito da L-glutamina e L-glutamato sobre o consumo, a conversão alimentar, a taxa de eficiência protéica, a eficiência de retenção de nitrogênio, o índice hepatossomático, a composição química corporal, a amônia e ureia sanguíneas. O aumento nos níveis de L-glutamina e L-glutamato nas dietas teve aumento linear sobre o ganho de peso e efeito quadrático na altura dos vilos. A adição de L-glutamina e L-glutamato melhora o ganho de peso e a altura das vilosidades intestinais de tilápia-do-nilo.

Utilização de levedura íntegra e seus derivados em dietas para juvenis de tilápia do Nilo

Neste trabalho, avaliou-se a adição de células íntegras de levedura e seus derivados em dietas para juvenis de tilápia do Nilo. Foram utilizados 144 juvenis machos de tilápia (peso médio de 52,1g) distribuídos em 12 tanques de fibra de vidro (250L), em delineamento inteiramente casualizado, composto por quatro tratamentos e três repetições. Os peixes foram alimentados ad libitum, duas vezes ao dia durante 60 dias, com dietas isoproteicas (28% PB) e isocalóricas (2.900kcal de ED kg-1) contendo levedura íntegra de cana-de-açúcar (LI), levedura autolisada (LA) e parede celular (PC) adicionados na proporção de 25% da proteína bruta total, comparadas com uma dieta controle (CO), sem adição de levedura. Não foram observadas diferenças significativas para conversão alimentar aparente e taxa de eficiência protéica. No entanto, o ganho em peso foi melhor nos peixes alimentados com as dietas LA (114,70g) e PC (131,03g), assim como em relação à taxa de crescimento específico (LA=1,79 e PC=1,93%), à proteína bruta no ganho de peso (LA=14,45 e PC=15,62%) e ao conteúdo corporal proteico (LA=14,89 e PC=15,67g 100g-1). As frações, a parede celular e a levedura autolisada de cana-de-açúcar podem ser utilizadas em dietas para juvenis de tilápia.

A preliminary study on the use of mannan oligosaccharides (MOS) in freshwater crayfish, Astacus leptodactylus Eschscholtz, 1823 juvenile diets

The effects of dietary mannan oligosaccharides (MOS) on the survival and growth of Astacus leptodactylus juveniles were evaluated. Experimental diets were prepared by using supplementation of 0 (Control), 1.5, 3.0, and 4.5 g MOS kg−1 commercial trout larvae diet containing 43 g kg−1 protein and 15.74 g kg−1 lipid. A. leptodactylus juvenile with an average total length of 3.6 ± 0.46 cm (TL) and average weight of 1.25 ± 0.43 g was stocked in 0.2-m2 aquariums at a rate of 50 crayfish/m2 and reared for 60 days at 22.8°C. The experiment consisted of four treatments with three replicates each. Each aquarium contained ten crayfish. Crayfish juvenile fed with 0, 1.5, 3.0, and 4.5 MOS attained 6.15 ± 0.49, 5.94 ± 0.29, 7.34 ± 0.39, and 5.94 ± 0.27 cm final total length and 50, 56.67, 46.67, and 50% survival rates, respectively. Moreover, molting frequencies in 0, 1.5, 3.0, and 4.5 g kg−1 MOS groups were detected as 44.44, 61.11, 83.33, and 38.88%, respectively. At the end of the experiment, a general enhanced growth performance (P 0.05) in percentage moisture, protein, and ash (wet-weight basis) in the tail meat of A. leptodactylus juvenile among treatments (diet) that averaged 82.3, 16.1, and 1.2%, respectively. However, lipid value was significantly different among the diets P < 0.05), with values between 0.13 and 0.32. From the current results, it could be advised to use MOS at the rate of 3.0 g kg−1 in A. leptodactylus juvenile diets.

Effect of early co-feeding and different weaning diets on the performance of cobia ( Rachycentron canadum) larvae and juveniles

Cobia ( Rachycentron canadum) is a very fast growing species. This can only be achieved if sufficient amounts of feed are provided from early larval development onwards. In this study, we examined the effects of early co-feeding and different co-feeding formulated diets on growth, survival and vitality of cobia larvae and juveniles. Two experiments were conducted to test the possibility of early co-feeding of the two formulated diets for cobia larvae (8–18 dph) and one experiment was conducted to compare the effect of three formulated diets for cobia juveniles (20–38 dph). During the larval stage, two formulated diets: Proton ® and an experimental diet (INVE, Belgium) were used along with live food from eight days post hatch (dph) and 13 dph compared to 18 dph as the control. Results from the study indicated that early co-feeding of Proton ® from eight dph had a significantly positive effect on growth ( P < 0.05), but not on survival and stress resistance in a salinity stress test ( P > 0.05) of cobia larvae. In the second trial, no significant difference ( P > 0.05) was detected between all treatments in terms of growth, vitality and survival. However, high mortality occurred in the treatment with the experimental diet as of 12 dph. The study suggested that early co-feeding of Proton ® to cobia larvae from eight dph is possible and research on the appropriate nutritional composition of weaning diets needs to be addressed. In the juvenile stage, three formulated diets, i.e. the experimental diet, Proton ® and NRD ® (INVE Aquaculture NV) were evaluated for growth performance and survival of early cobia juveniles (20–38 dph). The diets were manually introduced from 22 dph at a feeding frequency of every 2 h until satiation, while feeding of enriched EG Artemia was maintained until 30 dph. Average length and weight of the 38-dph juveniles fed the experimental diet were significantly higher ( P < 0.05) compared to larvae fed Proton ® and NRD ®. However, the coefficient of size variation as well as the cumulative stress index in a salinity challenge test was not significantly different ( P > 0.05). Survival in the Proton ® treatment was the lowest, while no significant difference was evident between the experimental diet and NRD ® treatments. The mortality rate of all three treatments had two peaks: one at the beginning of the experiment and one when live food feeding was discontinued. This result indicates that the nutritional requirements of cobia are age-dependent and prolongation of live food co-feeding during weaning may be necessary. The higher DHA/EPA ratio in the experimental diet can be a clue for the improvement of growth and survival of cobia during the weaning stage.