Exotic plus native: findings in an unscheduled fish duoculture

The development of native fish aquaculture represents an important alternative to mitigate ecological displacement generated by exotic fish. The introduction of native fish in polyculture systems with high commercial value fishes has provided a useful strategy for sustainable aquaculture development. The present study aims to provide information on tilapia, as an exotic species, and Dormitator latifrons, as a native species, in a duo culture not programmed as such. Using juveniles of Pacific fat sleeper D. latifrons leftovers from another experiment, we decide to analyze and report the biological feasibility of a duoculture system with this species and Nile tilapia (Oreochromis niloticus). Two hundred fifty organisms of each species were placed for 90 days in a concrete tank with a capacity of 50 m3 to evaluate the compatibility of these species. The biological variables measured were growth, survival, feed conversion rate, and protein efficiency. The findings suggest a good interaction between species, with adequate growths and a survival rate of 98%. No antagonistic behavior was observed during confinement, suggesting the duoculture of these species may represent a good alternative for tropical sustainable aquaculture.

Calculating the carbon footprint of the artisanal common hake fishery (Merluccius gayi gayi) in Caleta Portales, Valparaíso, Chile

Society's awareness of environmental issues increases every day. In this context, the concept of carbon footprint (CF) arises as a calculation tool that quantifies greenhouse gasses (GHG) emitted during the life cycle (LC) of a product. This calculation method is used in many productive sectors throughout the world; however, the Chilean fisheries sector has not notified the use of this tool or initiatives in that sense. This study performs a calculation of the CF of artisanal gillnet hake (Merluccius gayi gayi) fishery of the Caleta Portales, located in Valparaíso, Chile. The ISO 14040: 2006 methodology was used. The analysis was limited from the boat departure until the catch is landed, as a gate-to-gate life cycle assessment (LCA). The fuel consumption data and information related to the fleet were used as the main source of information. The Caleta Portales hake landings were 1,340.484 kg in 2011 and 703,411 kg in 2012. This fleet released into the atmosphere in 2011, 0.47 CO2 equivalent per kg of hake landed, and 0.58 kg CO2 eq, in 2012. It is the first result of CF reported in a Chilean fishery. This result can lead to an increase in the competitiveness of this hake fishery, as it can generate a positive impact on encouraging consumers to prefer the consumption from those places that have calculated the CF and are less than other food products.

Impact of unilateral eyestalk ablation on Callinectes arcuatus (Ordway, 1863) under laboratory conditions: behavioral evaluation

Eyestalk ablation allows the removal of neurohormones that inhibit early reproduction and decreases the time to complete the molting cycle. The present study evaluated the impact of unilateral eyestalk ablation on the behavior of blue crab breeders Callinectes arcuatus in the short term under laboratory conditions. Immature male and female crabs and individuals in the intermolt stage were collected in Ohuira Bay, Ahome, Sinaloa, Mexico. Three bioassays were performed: males, females, and male-females each with three treatments; control + xylocaine (50 μL, 5%), squash ablation + xylocaine (50 μL, 5%), ablation by string ligation + xylocaine (50 μL, 5%), each with three replicas and three periods of evaluation after the ablation procedure (10 min, 2 h, and 24 h). Kruskal-Wallis and Chi-square (χ2) tests were used to evaluate significances (P < 0.05) in the behavior of C. arcuatus. The sizes of blue crab C. arcuatus were 9.72 ± 1.0 cm of carapace width. The feeding behavior of the male-females bioassay was significant at 2 h (P < 0.05). The results obtained were satisfactory using two techniques, unilateral eyestalk ablation by squash and ligation in which pain and aggressiveness indicators were mitigated. Disorientation and aggressiveness in males were significant at 2 h (P < 0.05), and in females after 10 min, and 2 h after ablation (P < 0.05). In the male-females bioassay, aggressiveness was significant at 2 h (P < 0.05). Courtship and copulation were recorded in those crabs subjected to unilateral eyestalk squash ablation (13 and 8, respectively).

Distribution and abundance of Euphausia mucronata: development stages and its relationship with temperature and chlorophyll-a concentration

Euphausia mucronata abundance and distribution of the developmental stages (calyptopis, furciliae, juveniles, and adults) was analyzed as a function of seawater temperature and chlorophyll-a concentration between Paposo (25°S) and Coquimbo (30°S), Chile. Zooplankton samples were obtained using bongo nets during February of three consecutive years (2014-2016). The Q coefficient was used to explore the relationship between the distribution and abundance of the development stages of E. mucronata with the temperature recorded throughout the water column. The adults were considerably more abundant than the rest of the ontogenetic development stages during the study period. The abundance of adults decreased from February 2014 to 2016, having a negative correlation with temperature. Relative abundance of juveniles and larvae increased positively related to the total euphausiid abundance. The Q coefficient showed a significant association of all development states concerning the low-temperature intervals recorded throughout the seawater column. Q coefficient showed no association with chlorophyll-a concentration through the recorded intervals throughout the water column and neither with the vertical abundance and distribution of E. mucronata specimens.

Lactobacillus strains isolated from oysters improve the production of Crassostrea gigas larvae

One of the main problems in laboratories of oyster seed production occurs in the stage of settlement or fixation and metamorphosis of the larvae. The organisms develop drastic morphological and physiological changes at this stage, exposing them to attack by pathogenic microorganisms. Numerous studies indicate that before larval settlement to a substrate, they require bacteria to stimulate and induce the process. In this study, Japanese oyster (Crassostrea gigas) larvae were fed with combinations of microalgae and bacteria previously selected for their probiotic potential; their impact on survival, growth, and settlement was evaluated. Larvae D of 12 days old were provided by a private company and transported to the laboratory under controlled conditions. Probiotic bacteria Lactobacillus plantarum 69Cr, L. fermentum 101Cc, and L. casei 43Cg were reactivated on MRS and applied at a concentration of 1×104 CFU mL-1. Microalgae Isochrysis galbana and Chaetoceros calcitrans were grown in F2 medium and supplied at a concentration of 3×104 cells mL-1. Results showed, in all treatments, a survival range of 39-53%, growth of 300-310 μm, and 34-56.5% settlement. However, the best bacteria combined with I. galbana and C. calcitrans was L. plantarum 69Cr with a 54% survival, 310 μm growth, and 56.5% settlement. It is concluded that the combination of L. plantarum 69Cr with I. galbana and C. calcitrans has the potential to be used in the production of Japanese oyster larvae.

Persistent organic pollutants (POPs) in fish from two coastal lagoons of the central Mexican Pacific

Mexico has a great variety of aquatic ecosystems; however, most of them present significant contamination levels. Despite the efforts to monitor toxic and bioaccumulative persistent pollutants, they are still insufficient and outdated data from Mexican coasts, especially in polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs), due to the number of aquatic bodies that have received little or no attention. In this regard, the Mexican Pacific's coastal zones and their aquatic ecosystems monitoring PCBs and PAHs in biota is critical because it allows us to estimate the potential risk to human health. This work aimed to determine the total concentration of polychlorinated biphenyls (ΣPCBs) and total polyaromatic hydrocarbons (ΣPAHs) in the muscle of fish collected in two coastal lagoons of the central Mexican Pacific and to determine the non-carcinogenic risk ratio (HQ) based on the monthly per capita consumption of national fish and the consumption of fish associated with fishing communities in Mexico. It was found that the potential risk for fishing communities is considerably higher and correlates to the rate of fish consumption, highlighting their vulnerability to these contaminants.

Histological structure of the digestive tract and digestive enzymatic activity of juvenile Pacific seahorse (Hippocampus ingens)

The histological structure, histochemical features, and enzymatic activity of the digestive tract of juvenile Pacific seahorse (Hippocampus ingens) are described to provide information during the cultivation of this species. Serial histological sections were stained with either hematoxylin-eosin, alcian blue-PAS, toluidine blue, Sudan black, Masson's trichome, and ninhydrin-Schiff to describe the general features and the presence of glycogen, mucopolysaccharides, lipids, muscle layers, and proteins, respectively. The enterocytes height and the mucosal villi height in the esophagus and intestines were measured. Additionally, the digestive enzymes trypsin, chymotrypsin, lipase, amylase, aminopeptidase, acid phosphatase, and alkaline phosphatase activities were recorded. The esophagus showed two distinctive regions, the anterior with numerous mucous cells secreting acid mucins and the posterior with longitudinal folds and no mucous cells. The intestine was differentiated into three regions. The anterior showed goblet cells secreting acid and neutral mucins, while the middle and posterior regions presented goblet cells secreting only acid mucins. The activity of aminopeptidase, chymotrypsin, and amylase showed low levels, while the trypsin and acid phosphatase activity levels were intermediate. Lipase and alkaline phosphatase showed the highest activities. The results point that juvenile H. ingens presents a digestive structure similar to other teleost species. The high levels of lipase suggest that juvenile H. ingens have high requirements for lipids during this stage.

Influence of different concentrations of chia (Salvia hispanica) and flaxseed (Linum usitatissimum) meal on fillet fatty acid profile of Nile tilapia (Oreochromis niloticus)

The nutritional quality of tilapia fillet is characterized by low omega-3 polyunsaturated fatty acids (n-3 PUFAs). The objective of the present study was to evaluate the effect of different dietary concentrations of chia (Salvia hispanica) and flaxseed (Linum usitatissimum) meal on the omega-3 fatty acid content of tilapia (Oreochromis niloticus) fillet. Six experimental diets incorporating 5, 10, and 15% chia or flaxseed meals, respectively, were given to the fish (238.36 ± 7.61 g, initial weight) for 45 days before harvesting. The α-linolenic acid (ALA) and n-3 PUFA contents in the fillet differed significantly among diets (P < 0.05). Diets containing 15% chia or flaxseed meal had the highest concentrations of ALA (4.80 and 4.75%, respectively) and n-3 PUFA (13.65 and 15.92%, respectively). Thus, chia or flaxseed meal dietary inclusion increased the ALA and n-3 PUFA contents in the tilapia fillet. Chia or flaxseed meals are useful and potential alternatives to improve the nutritional value of O. niloticus fillets.

Digestible protein requirements for maintenance, growth, and efficiency of protein utilization in pacu (Piaractus mesopotamicus) juveniles: an exponential nitrogen utilization model

The present study aimed to estimate digestible protein (DP) requirements for maintenance and growth and assess the efficiency of protein utilization in pacu (Piaractus mesopotamicus) juveniles. A complete randomized design consisted of seven treatments, and five replicates (tanks) per treatment was used. After a one-week acclimation period, 350 pacu juveniles of 27.48 ± 1.8 g (initial average body weight - BW) were equally distributed among 35 tanks (10 fish per tank) of 450 L. Fish were fed with seven graded digestible protein levels (64.5, 111.8, 164.6, 217.1, 264.4, 316.2 and 369.5 g kg-1) three times a day until apparent satiation for 120 days. The monomolecular model parameters including nitrogen maintenance requirement (NMR) (37.76 mg BW0.67 kg-1 d-1), daily nitrogen deposition (ND) (194.8 mg BW0.67 kg-1 d-1), and protein intakes (based on metabolic BW) of 1638, 1902, and 2241 mg kg-1BW0.67 d-1 for 75, 80 and 85% maximum theoretical nitrogen retention (NRmaxT), respectively and the efficiency of protein utilization (529×10-6) were estimated through the relationship between nitrogen intake (NI) and ND. The digestible protein requirements for 75, 80, and 85% of NRmaxT were estimated as 187, 217, and 256 g kg-1 respectively by the monomolecular model based on the daily feed intake of 2% of live BW of pacu juveniles.