José Manuel Mazón-Suástegui

Changes in the composition and diversity of the bacterial microbiota associated with oysters (Crassostrea corteziensis, Crassostrea gigas and Crassostrea sikamea) during commercial production

The resident microbiota of three oyster species (Crassostrea corteziensis, Crassostrea gigas and Crassostrea sikamea) was characterised using a high-throughput sequencing approach (pyrosequencing) that was based on the V3-V5 regions of the 16S rRNA gene. We analysed the changes in the bacterial community beginning with the postlarvae produced in a hatchery, which were later planted at two grow-out cultivation sites until they reached the adult stage. DNA samples from the oysters were amplified, and 31 008 sequences belonging to 13 phyla (including Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes) and 243 genera were generated. Considering all life stages, Proteobacteria was the most abundant phylum, but it showed variations at the genus level between the postlarvae and the adult oysters. Bacteroidetes was the second most common phylum, but it was found in higher abundance in the postlarvae than in adults. The relative abundance showed that the microbiota that was associated with the postlarvae and adults differed substantially, and higher diversity and richness were evident in the postlarvae in comparison with adults of the same species. The site of rearing influenced the bacterial community composition of C. corteziensis and C. sikamea adults. The bacterial groups that were found in these oysters were complex and metabolically versatile, making it difficult to understand the host-bacteria symbiotic relationships; therefore, the physiological and ecological significances of the resident microbiota remain uncertain.

Suspension culture of catarina scallop Argopecten ventricosus (=circularis) (Sowerby II, 1842), in Bahia Magdalena, Mexico, at different densities

Abstract Hatchery-reared spat (5 mm) of catarina scallop ( Argopecten ventricosus (=circularis )) were cultured in plastic trays suspended from a long line at Rancho Bueno, Baja California Sur, Mexico. The mean surface temperature range was 20 to 29 °C and salinity remained steady at 37 ppt during the 320-day experiment. Every 1 or 2 months, the trays and the scallops were cleaned, the scallops measured, and survival recorded. Three densities were tested on each of the culture stages; called nursery (from day 1 to day 80), intermediate (80 to 136) and growout (136 to 320). Average densities were 1500, 2500, and 4000 scallops/m 2 for the nursery stage; 400, 700, and 1000 for the intermediate; and 150, 250, and 400 for the growout stages. At the end of nursery and intermediate stages, scallops of the modal size class were selected to begin the following stage using scallops of homogeneous size. In the nursery stage, growth rate was higher at low density. At the intermediate stage, growth rates were highest in low and medium densities ( P P 91% at the end of the experiment and did not correlate with density. Mortality began to occur in animals older than 8 months, during the spawning season at the onset of summer. Two hypothetical growth curves were constructed from the data taking for each stage those densities producing the fastest and slowest growth. Results indicate maximum shell length could be attained in 273 (fastest) and 398 (slowest) days. A cost analysis indicates that, regardless of the longer time, culturing scallops at high density would be less expensive than at low density, taking into account the muscle-weight loss caused by crowding.

Prospective Culture of the Cortez Oyster Crassostrea corteziensis from Northwestern Mexico: Growth, Gametogenic Activity, and Condition Index

Abstract This study examined growth, gametogenic activity, condition index, as well as the relationship of the life cycle to environmental parameters of the Cortez oyster Crassostrea corteziensis, which was cultured for 25 mo in the lagoon of Las Guásimas (Sonora, Mexico). We used oocyte diameter and cytological characteristics of the gonad to determine reproductive stages in females and males. The condition index was used to describe the oysters physiological health. Temperature, salinity, seston, and chlorophyll a, b, and c were recorded at the study site. The Cortez oyster had isometric shell growth, reaching 103.2 ± 1.82 mm height and 150.3 ± 4.98 g total weight. Data were adjusted to the von Bertalanffy growth equation (L∞ = 132.2 mm and K = 1.08 y−1), and survival was about 70%. This native species exhibited a distinctive gametogenic cycle, with the beginning and end of the cycle controlled by seawater temperature fluctuation (15–33°C), which once started, is continuous over a 9-mo period (March to November). Elevated temperature (>25°C) produced high gametogenic activity, exhibiting primary, growing, and mature oocytes, and partial spawning in April, September, and November. The peak spawning event occurred in August, when seawater reached peak temperatures of 31°C to 33°C, which was followed by a significant reduction of the condition index. During winter, storage of nutrients took place, and this appears to be used in the following season for gametogenesis. In general, the condition index was high throughout the study period. Energy for growth and reproduction came from phytoplankton blooms in summer and high concentration throughout the year of nonchlorophyll particulate organic matter. Observations show that this oyster is a protandrous species. High survival, elevated yields, and a long, continuous gametogenic cycle indicate that C. corteziensis has importance in aquaculture in Gulf of California.

Isolation and in vitro selection of actinomycetes strains as potential probiotics for aquaculture.

Aim: This study was designed to describe a series of in vitro tests that may aid the discovery of probiotic strains from actinomycetes. Materials and Methods: Actinomycetes were isolated from marine sediments using four different isolation media, followed by antimicrobial activity and toxicity assessment by the agar diffusion method and the hemolysis of human blood cells, respectively. Extracellular enzymatic production was monitored by the hydrolysis of proteins, lipids and carbohydrates. Tolerance to different pH values and salt concentrations was also determined, followed by hydrophobicity analysis and genetic identification of the most promising strains. Results: Five out of 31 isolated strains showed antimicrobial activity against three Vibrio species. Three non-hemolytic strains (N7, RL8 and V4) among these active isolates yielded positive results in hydrophobicity tests and exhibited good growth at salt concentrations ranging from 0% to 10%, except strain RL8, which required a salt concentration >0.6%. Although these strains did not grow at pH<3, they showed different enzymatic activities. Phylogenetic analysis revealed that strains N7 and V4 have more than 99% identity with several Streptomyces species, whereas the closest matches to strain RL8 are Streptomyces panacagri and Streptomyces flocculus, with 98% and 98.2% similarity, respectively. Conclusion: Three actinomycetes strains showing probiotic-like properties were discovered using several in vitro tests that can be easily implemented in different institutions around the world.

Digestive enzymes of the Californian two-spot octopus, Octopus bimaculoides (Pickford and McConnaughey, 1949)

Octopus bimaculoides is an important commercially fished species in the California Peninsula with aquaculture potential; however, to date limited information is available regarding its digestive physiology. The objective of this study was focused on biochemically characterizing the main enzymes involved in the digestion of O. bimaculoides. Optimum pH, temperature and thermostability were determined for amylases, lipases, trypsin and chymotrypsin; optimum pH and protease inhibitor effect were assessed for acidic and alkaline proteases, and the effect of divalent ions on trypsin and chymotrypsin activity was evaluated in enzymatic extracts from the digestive (DG) and salivary glands (SG) and crop gastric juices (GJ). High amylase activity was detected in GD and GJ whereas this activity is very low in other cephalopods. Salivary glands had the greatest activity in most of the enzyme groups, showing the importance of this organ in digestion. Optimum pH was different depending on the organ and enzyme analyzed. The optimum pH in DG was 3 showing the predominance of acidic proteases in the digestion process. All enzymes were resistant and stable at high temperatures in contrast with other marine species. Trypsin and chymotrypsin activity were highly incremented with the presence of Mg2+, Co2+, Cu2+ and Zn2+ in some tissues. The inhibitor assay showed the importance of serine proteases, metalloproteases and aspartic proteases in the digestive process of this species. This study is the first in assessing the main digestive enzymes of O. bimaculoides and in remarking the importance of other digestive enzyme groups besides proteases in octopuses.

Chapter 29 - Scallop Fisheries and Aquaculture in Mexico

This chapter describes the three most important Mexican scallop species (lions paw: Nodipecten subnodosus; Pacific calico scallop: Argopecten ventricosus; Vogdes scallop: Euvola vogdesi), their ecology, fisheries and aquaculture. All commercially important scallops in Mexico occur in the Pacific Northwest and Gulf of California, especially in the lagoon systems along the coast in shallow waters to depths of about 100 m. The three scallop species are fast growing, reproduce early in life, and form large banks that have been commercially exploited over the past decades by hooka-diving from small fibreglass skiffs with outboard engines. As happened in many scallop fisheries around the world, exploitation is characterised by boom and bust phases. Commercial fisheries of Mexican bay scallop started in the early 1980s and represented the most important mollusc fishery in the country from 1985 to 2013, when the banks in Magdalena bay were diminished so much, that the fishery was closed. Vogdes scallop was only locally exploited for a short time, the lions paw, however, has sustained a small commercial fishery in Ojo de liebre and Guerrero Negro lagoons from the early 1990s to 2010 with a maximum production of about 150 mt of meats. In 2010, the population crashed, probably due to a disease, the cause of which is still being investigated. This species was also fished at different sites in the Gulf of California (Loreto, Bahia de Kino), but on a much smaller scale. Today, all scallop fisheries in Mexico are in a serious crisis and are deemed unsustainable. Therefore, large efforts have been undertaken to develop commercial aquaculture of A. ventricosus and N. subnodosus. While hatchery techniques for the former are fully developed and commercial spat production has been accomplished routinely, hatchery production of the latter is still on a small scale, and no commercial spat supply is as yet available, despite a large number of scientific studies on the subject. Small-scale pilot and commercial cultures of both species have been conducted at >15 sites on the Baja California Peninsula and the coasts of Sonora and Sinaloa over the past two decades, with varying results. No active scallop cultures are in operation as of 2015, which shows that they have not been commercially viable for the most part. Lack of spat production, site selection, El Nino years, diseases, handling, market failures, competition with the capture fishery and mismanagement have been quoted as possible reasons, and the Mexican government does not have a comprehensive programme to promote scallop aquaculture. Unfortunately, the large body of scientific studies on scallop aquaculture in Mexico has not translated into an economic alternative for the aquaculture and fishing industry in the region. As fisheries in the region are clearly in decline, efforts should be strengthened to promote sustainable aquaculture of native species and thereby improve the livelihood of coastal communities.

Internal Energy Management Associated with Seasonal Gonad Development and Oocyte Quality in the Horsemussel Modiolus capax (Bivalvia; Mytilidae)

ABSTRACT Qualitative and quantitative histological and histochemical techniques were used to study seasonal dynamics of energy reserves associated with gonad development and oocyte quality in the horsemussel Modiolus capax in Bahía de La Paz during the period February 2013 to January 2014. Thirty adult mussels were collected on a monthly basis and evaluated for gonad developmental stages and changes in oocyte features (theoretical diameter, nucleus/cytoplasm ratio, lipid index, and carbohydrate index). The overall somatic coverage area versus gonad coverage area and energy reserves in the gonad (carbohydrates and neutral lipids) was also analyzed. In summer (26.5 ± 1.4°C and 2.3 ± 0.7 mg m-3 chlorophyll a), oocytes achieved greater sizes that were significantly correlated with higher lipid reserves in the gonad. This suggests that female gonads have superior breeding capacity in summer, compared with those in the autumn and winter periods, when oocyte performance and ovarian energy reserves were minimal. The evidence indicates that M. capax follows a conservative strategy to sustain gametogenesis relying on energy reserves previously stored in somatic tissue between autumn and winter. By contrast, optimal reproductive performance between April and August associates more with decreasing somatic coverage area and increasing gonad coverage area; this reflects a period of energy (lipids) transfer from storage tissues to the gonad to fuel gametogenesis. These results help establish the biological basis for gonad conditioning and maturation of M. capax to ensure continuous production of spat at the laboratory.

Carbohydrate-Rich Diets Meet Energy Demands of Gametogenesis in Hatchery-Conditioned Mussels (Modiolus capax) at Increasing Temperatures

ABSTRACT This study reports the basic nutritional requirement of subtropical Modiolus capax broodstock conditioned under nine diet—temperature treatments. The value of carbohydrate-rich diets was not only assessed to ensure maturation outside of the main breeding season but also to understand the interaction between diet—temperature over conditioning periods larger than the 30 days usually recommended for tropical bivalves. The experimental design included a natural diet prepared with a blend of the microalgae Tisochrysis lutea and Chaetoceros calcitrans (Micro100) and two carbohydrate-enriched diets composed of Micro100 + wheat flour (MicroW) at 7% total dry weight of body tissues and Micro100 + cornstarch (MicroC) at 7% total dry weight of body tissues. Maximum gonad development occurred in mussels fed MicroC at higher temperatures (26°C) where the highest frequency of partial spawning accompanied the highest lipid content in gonad and lower carbohydrate content in somatic tissues. This result reflects an early maturation compared with brood stock fed the natural Micro100 diet at 24°C. Lower temperatures (22°C) delayed maturation in all treatments and favored accumulation of carbohydrate reserves in somatic tissues with the MicroC diet. Natural diets supplemented with carbohydrate-rich sources by cereal flours are reliable alternatives to fuel and sustain gametogenesis in M. capax broodstock at high temperatures and to increase carbohydrate reserves in somatic tissues at low temperatures.

Streptomyces effect on the bacterial microbiota associated to Crassostrea sikamea oyster.

To determine the composition and diversity of the microbiota associated to Crassostrea sikamea treated during 30 days with Streptomyces strains N7 and RL8.