Effects of stocking density on intermediate culture of the razor clam Ensis arcuatus (Pharidae: Bivalvia)

Commercial production of most bivalve species involves a phase of intermediate cultivation during which juveniles are grown under protected conditions until they can be transferred to the final grow‐out location. Consequently, the aim of this study was investigating the effect of density on growth and survival in the intermediate culture of the razor clam Ensis arcuatus in raft. Two series of experiments were performed, using in the first experiment two holding systems: 5‐L plastic bottles and PVC cylinders, both perforated, covered with a 1 mm mesh net to prevent razor clam escape and a 10‐cm layer of coarse grained sand (300–1200 μm grain diameter). In this trial, two stocking densities were tested: 0.15 and 0.30 kg m^?2. In the second one‐two densities were essayed (0.62 and 1.24 kg m^?2) in the PCV cylinders. In the first experiment after 27 of trial higher growth in cylinders at low density was observed. At the end of this trial all juveniles died in the 5‐L plastic bottles and higher growth and survival were recorded in the cylinders at low density. In the second experiment, significant differences in growth and survival were found on day 70, with the best results at low density. Five‐L plastic bottles must be rejected as holding system for the intermediate culture of E. arcuatus and the PVC cylinders at low densities could be a good alternative. At the end of the experiment razor clams reached the adequate size for their transfer into the grow‐out system.     

Histopathological and behaviour effects of formaldehyde treatment in juvenile mullet,Mugil liza (Valenciennes)

Considerable losses may be related to diseases caused by parasites in aquaculture. Formaldehyde (37% gas dissolved in water) is an effective chemotherapeutic, widely used to control ectoparasites in fish. However, for many species of fish used in aquaculture, the control of external parasites and the deleterious effects of formaldehyde in short‐term baths are still uncertain. In order to clarify some gaps, 1 h‐prophylactic baths (67.5, 135, 270, 405 and 540 mg L^?1 formaldehyde in triplicate) were performed in juvenile mullet, Mugil liza (Valenciennes). Results showed that prophylactic baths of 135 mg L^?1 formaldehyde by 1 h did not cause death in tested mullets. At this concentration, histopathologies were mild and fish survival was high. However, fish exposed to increasing concentrations of formaldehyde presented severe histopathologies in the gills besides behavioural and morphological alterations. The histopathological and behavioural implications of formaldehyde use in aquaculture are discussed.     

Genetic and morphological characterization of Acroceras macrum Stapf

Acroceras macrum is a warm‐season grass used for pastures, and it has high nutritive value. The scarce genetic and reproductive information about this grass is limiting its breeding for forage. The objective of this research was to determine the number of genotypes and cytotypes present in a collection established in Argentina, and to estimate the diversity of this species based on molecular markers, and morphological and agronomic characteristics. The number of genotypes among forty‐seven accessions was determined using ISSR markers. The identified genotypes were further characterized for ploidy levels. In addition, the genetic distances among them were estimated with ISSR markers. They were also propagated and planted into the field following a randomized complete block design with four replications, and a group of sixteen morphological and agronomic variables were evaluated. A total of twenty‐seven genotypes were identified in this collection; twenty‐two genotypes were tetraploid (2n = 4x = 36) and five were hexaploid (2n = 6x = 54). These two cytotypes were found clearly separated by both genetic and phenotypic characteristics. Above‐ground biomass, internode length, initial growth and number of spikelets per inflorescence were the most variable traits. The high diversity present in this collection will allow for the initiation of a breeding programme for A. macrum.     

Using cornstarch in microparticulate diets for larvicultured tropical gar (<Emphasis Type="Italic">Atractosteus tropicus</Emphasis>)

Aquaculture in Mexico has been developed by the cultivation of commercial species. In Tabasco, the cultivation of native species is mainly limited by the lack of nutrition studies to support its crop profitability. Among these species is the tropical gar (Atractosteus tropicus), which has great potential for cultivation. However, the nutritional value of carbohydrates in diets for this species which contribute to improved growth and survival, have not been evalulated,. Thus, in the present investigation, isoprotein and isolipid diets have been designed based on the substitution of cellulose by corn starch (D1: 0 % starch–15 % cellulose, D2: 7.5 % starch–7.5 % cellulose and D3: 15 % starch–0 % cellulose) and compared with a commercial trout diet (45 % protein and 16 % lipids). A total of 1800 larvae (0.008 ± 0.002 g and 10.5 ± LT 0.126 mm) were used, distributed in a recirculation system in order to evaluate growth and survival for 30 days. The results show higher growth and survival of 97 % of larvae fed the D3 diet, while cannibalism in the species was mitigated. Major digestive enzyme activities occurred (acid protease, alkaline protease, trypsin, chymotrypsin, leucine aminopeptidase, carboxypeptidase A, lipase, α-glucosidase and amylase) for larvae fed D3. It is concluded that the contribution of corn starch (15 %) replacing cellulose in the diet improves growth and survival of this species.     

Characterization,specificity and sensibility of produced anti-<Emphasis Type="Italic">Rhamdia quelen</Emphasis> vitellogenin in Brazilian fish species

Endocrine-disrupting chemicals (EDCs) are widespread used and can interfere on hormone regulation with adverse consequences for both biota and human. Vitellogenin (vtg) is a yolk precursor protein synthesized by the liver in response to estrogen. In order to characterize the vtg of tropical fish Rhamdia quelen and establish a molecular biomarker, adult male individuals were exposed to 17-β-estradiol (E₂) for vtg induction and anti-R. quelen vtg polyclonal antibodies production. Vitellogenic female fish were used as positive control group. E₂-induced vtg was characterized as a glycolipophosphoprotein of high molecular mass with peptide mass fingerprint very similar in E₂-exposed male and vitellogenic female fish. A polyclonal serum containing anti-R. quelen vtg antibodies was produced and showed high specificity and sensibility to detect the vtg of three fish species: R. quelen, Piaractus mesopotamicus and Prochilodus lineatus. Wildlife and laboratory studies reported that EDCs released into the environment may alter the levels of plasma vtg in male fish, making this protein a valuable biomarker of xenoestrogens exposure. Then, we propose the use of anti-R. quelen vtg as a tool for biomonitoring studies and water quality assessment in Brazil and South American countries where the three fish species occur.     

An insight on Octopus vulgaris paralarvae lipid requirements under rearing conditions

In this study, two new alternative preys: Grapsus adscensionis zoeae (as sole prey) and Palaemon elegans zoeae (in cofeeding with Artemia sp.), as well as, Artemia sp. juveniles were used as feed for octopus paralarvae, as a way to understand its lipid requirements. Total lipid (TL) content, lipid class (LC) and fatty acid (FA) profiles of preys, octopus hatchlings and 9‐day‐old paralarvae were analysed. Growth and survival of the paralarvae were also determined. Regardless the prey provided, a notable shift in the lipid profile of paralarvae was registered after 9 days of rearing. The highest index of growth rate (IGR) recorded when decapod crustacean zoeae were supplied might have some relation with levels of 20:4n‐6 (ARA) and DHA/EPA ratio observed. In this sense, Grapsus adscensionis zoeae leaded to a higher content of ARA and a lower content of EPA, which may indicate a possible competition between these two FA. For that a balanced EPA/ARA ratio might be significant in this species nutrition without disconsidering DHA levels as an essential fatty acid. Finally, the changes observed in paralarvae FA profile might not only be related to prey FA profile, but also with changes occurring in the lipid classes contents.