Pedro J. Barón

Analysis of the ontogenetic variation in body and beak shape of the Illex argentinus inner shelf spawning groups by geometric morphometrics

In this paper we analysed size and shape differences of body (mantle and fins) and inferior beak of the squid Illex argentinus from two Patagonian inner-shelf spawning groups. A new method was developed to reconstruct three-dimensional coordinates based on the 2-D projection of the beak on a plane. Shape of the beak did not vary between groups, sexes and maturity condition of individuals. Also, no beak shape changes were observed through the ontogeny. In contrast, as larger and heavier squids were considered in shape analysis, body widened near the fin insertion, and fin area increased. Our results suggest that shape adaptations of I. argentinus through the ontogeny reflect modifications to optimize swimming performance rather than to increase gamete holding capacity.

Schedule of Reproductive Events and Maturity at Size of the Patagonian Stone Crab Platyxanthus Patagonicus (Brachyura, Platyxanthidae)

The most significant events of the reproductive cycle of the Patagonian stone crab, Platyxanthus patagonicus, were studied in specimens sampled in northern Patagonian gulfs from August 2004 to May 2006. Male and female crabs were assigned to stages of a scale of gonad maturity. Females were also classified according to the presence/absence of embryos on the pleopods and of spermatic content in the spermathecae. Ogives were fitted to maturity at size data. The highest frequency of pre-ovigerous females and spermathecae with hardened seminal contents occurred during the fall and winter. Fifty percent of the females reached ovarian maturity at 66.4 mm CW. Ovigerous females were frequent from mid-fall to mid-spring, peaking during early winter and mid-spring, and were unusual or absent during the summer months. Post-ovigerous females were present in samples in all months but May and June 2005, being frequent from late-spring to early-fall. Specimens with spent ovaries were common in all seasons but summer, while those with mature or recovering ovaries were present in samples taken in all months but August 2004 and May-June 2005. Fifty percent of the males reached testes maturity at 54.7 mm CW. Males larger than this size showed mature gonads year round, but a pulse of individuals with recovering testes was observed during the winter of 2005 and early-fall of 2006. Our results show that mating occurs during the fall months, spawning and embryonic incubation extends from fall to early spring, and hatching takes place during late-spring and early-summer.

Multiple spawning and length of embryonic development of Munida gregaria in northern Patagonia (Argentina)

Munida gregaria is a small galatheid widely distributed around the southern hemisphere, considered a key species in food webs of coastal and shelf marine ecosystems. Previous studies conducted at 55°S and 46°S on the Atlantic coast of South America, have shown that the species can adapt its reproductive patterns to different environmental conditions. The objectives of this work are to complete this analysis by determining: (1) the reproductive season span; (2) the potential of the species to produce multiple clutches of eggs; (3) the length of its embryonic development; and (4) based on previous objectives, the potential number of clutches produced by M. gregaria by reproductive season in the northern range of its coastal distribution (42–43°S, northern Patagonia). In this region, brooding females were present from June to December, representing more than 80% of total females between July and October. Females presented previtellogenic oocytes beginning maturation just after egg extrusion, and fully developed vitellogenic oocytes just before hatching. From November to February increasing proportions of females showed signs of athresia and resorption of mature oocytes. The complete embryonic development of M. gregaria lasted 26–29 days at 11oC constant temperature. Considering the pattern of synchronous ovary re-maturation and embryonic development, the length of embryogenesis at water temperatures typical from costal waters off northern Patagonia during the breeding season, it is concluded that female M. gregaria have the potential to consecutively lay more than three egg clutches per reproductive season.

Seasonal abundance and vertical distribution of crab larvae from northern Patagonia (Argentina): implications for their transport in a biogeographic boundary region

Abstract In species with meroplanktonic larval phases, some reproductive traits (i.e. seasonality and larval behaviour) interact with hydrographic features to determine larval transport. This work reports the seasonal, diel and ontogenetic changes in vertical distribution of crab larvae in the boundary region between the Argentine and the Magellanic biogeographic provinces of the Atlantic coast off northern Patagonia (Golfo Nuevo; 42.75°S, 65.00°W). Larval seasonality was studied from 47 plankton hauls taken from August 2004 to July 2005. Vertical distribution was studied from 45 stratified plankton hauls carried out in August 2005, December 2005 and April 2006. Crab larval stages were detected throughout the year, but abundance was higher from midwinter to midsummer. Species from southern regions – Munida gregaria, Peltarion spinosulum and Halicarcinus planatus – were abundant during winter and aggregated mainly near the surface, regardless of the hour of the day. In contrast, species from northern regions – Platyxanthus patagonicus, Ovalipes trimaculatus, Leucippa pentagona, Leurocyclus tuberculosus, Cyrtograpsus spp. and Pachycheles chubutensis – were abundant during spring and summer and were usually aggregated near the surface during the night and dispersed in subsurface layers during the day. Ontogenetic changes in vertical distribution were not observed. Residual currents reported in the area (3–6 km·day−1) and duration of larval life (approximately 15–70 days) suggests a minimum potential transport on a 100-km scale. Biological information reported in this work could be explicitly incorporated in a circulation model to accurately predict larval transport and connectivity.

Feeding physiology of the Argentine mussel Mytilus edulis platensis (d'Orbigny, 1846): does it feed faster in suspended culture systems?

The feeding behavior of Mytilus edulis platensis, one of the most important aquaculture resources on the East Coast of southern South America, was studied by analyzing clearance rate (CR) and ingestion rate (IR) to test the hypothesis that cultivated mussels can attain higher clearance and ingestion rates than their wild counterparts. A number of morphometric relationships between cultivated and wild mussels were also compared. Gill surface (GS) growth relative to length (L) is isometric in M. e. platensis, with no significant differences between wild and cultivated mussels. At low food concentrations (<15 Chaetoceros gracilis cells μl−1), the CR is maximum and similar in both cultivated and wild mussels, decreasing when the concentration of experimental food surpasses a threshold level. This concentration threshold is higher in cultivated mussels than in wild ones. While culture conditions do not affect either GS growth or potential CR, they do affect CR regulation patterns in response to fluctuations in food concentration, allowing the attainment of higher maximum IR.

Pasteurization Conditions and Evaluation of Quality Parameters of Frozen Packaged Crab Meat

ABSTRACT Ovalipes trimaculatus is a crab recognized as a new resource with fishing value to obtain frozen products. Pasteurization conditions of meat crab at temperatures below 85ºC (60, 72, and 82ºC) were established to achieve better quality attributes in the frozen product. The lethality curves of Staphylococcus aureus and Listeria monocytogenes were measured, and the decimal reduction times (D) and Z values were determined. Heat transfer during the pasteurization process of pouches containing crab meat was simulated using a computational code in finite elements, and the mathematical model was experimentally validated. Thermal histories were coupled to the microbial lethality kinetics of the most heat resistant pathogen microorganism in order to establish pasteurization times necessary for the process system design. The predicted pasteurization conditions were microbiologically validated. The pouches were frozen under industrial conditions and stored at −22ºC for 1 year. The influence of the type of packaging (vacuum and nonvacuum plastic pouches) on physicochemical and sensory quality parameters of frozen crab meat (color, exudate, lipid oxidation, water holding capacity, and overall acceptability) were analyzed observing better performance under vacuum conditions.