Studies focusing on the specific identification of the taxonomic cast within the genus Opisthonema are scarce and contradictory, in spite of this species commercial importance and of the potential ecological impact that fisheries may have on the pelagic ecosystem. In this study, the specific composition of thread herrings Opisthonema (O. bulleri, O. medirastre, and O. libertate) in the southeastern region of the Gulf of California was identified using meristic characters, morphometric data, and mtDNA sequences. In this paper we supported the hypothesis that the commercial catch comprises three evolutionary entities with meristic and morphometric differences. The results were based on the number of ceratobranchial gill rakers, the presence of spicules on the gill rakers, the form of insertion of the gill rakers base onto the ceratobranchial segment, the geometric morphometrics of body shape, and the genetic distances from a fragment of Cytochrome Oxidase Subunit I gene (COI) of mtDNA. Specimens of Pacific thread herring were obtained from landings of the small pelagic fleet at Mazatlan, Sinaloa during 2011-2012. Taxonomic categories were assigned to 1060 individuals according to the measurement of meristic characters. A total of 228 thread herrings O. bulleri, (n = 76), O. medirastre (n = 76), and O. libertate (n = 76) were used in the morphometric analysis, and 25 specimens (O. bulleri n = 8, O. medirastre n = 7, and O. libertate n = 10) were used for genetic comparisons. The morphometric results showed differences among the three groups that had been previously identified using meristic characters, giving support to the existence of three discrete morphotypes. The percentage of sequence divergence of the COI gene supports the existence of three clades. Genetic distances were considerably lower within each clade than between clades. The results of this study provide sufficient evidence for the existence of three Pacific thread herring species in the southern Gulf of California.U.S.

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<p><strong>Background. </strong>The <em>Macrobrachium tenellum</em> prawn is captured and commercialized by local fishermen along its distribution interval.  It is considered an euryhaline palemonid prawn.  If its cultivation is wanted, the best conditions for its growth and reproduction should be investigated, including proper intervals of temperature, salinity, density and dissolved oxygen. <strong>Objective.</strong> To determine the effect of two different salinities (0 and 15PSU) on the physiological rates that balance the energy equation in <em>M. tenellum</em> adults and to determine if energy use is more efficient under isosmotic conditions. <strong>Methodology</strong>. Specimens were collected in Guasave, Sinaloa, Mexico, in July 2018 and taken to the Aquaculture Laboratory at UAdeO.  The energy balance was calculated in hyposmotic (0 PSU) and isosmotic (15 PSU) conditions at preferred temperature (28.5 ± 1 ° C). The energy invested in respiration and excretion, the feces lost and the ingested food and the growth potential was calculated using a semi-open respirometer. <strong>Results.</strong> The highest energy expenditure occurred in the respiratory rate (routine metabolism), then feces production and finally ammonia production in both salinities. The highest total energy expenditure was observed in fresh water. The highest amount of energy directed to the growth or reproduction was observed in brackish water (15 PSU), as well as the highest rate of food ingestion. <strong>Implications.</strong> Knowledge on the use of energy in the feed in the best saline condition for its cultivation useful for culture purposes. <strong>Conclusion.</strong> The saline condition in where more energy is channeled for the growth of <em>M. tenellum</em> is 15UPS (isosmotic point) and in it is also in where less energy is spent.</p>

La liseta Mugil curema está entre las principales especies que explota la pesquería artesanal en la costa mexicana del Océano Pacífico. Abordar aspectos reproductivos de las especies por zona de pesca reducirá el sesgo en la evaluación del estado de sus poblaciones. El objetivo del presente estudio fue describir el ciclo reproductivo y estimar algunos parámetros biológicos de la liseta en dos sitios de pesca de la costa de Baja California Sur. Mensualmente, se muestreo la captura de Bahía de La Paz (BLP) y Bahía Magdalena (BM), durante 2010-2013. Se analizó histológicamente la maduración gonadal y se describió el ciclo reproductivo. Se estimaron, el índice gonadosomático (IGS), factor de condición (FC), índice hepatosomático (IHS), la relación peso-longitud y longitud promedio de madurez sexual (L50%). La longitud total de los peces varió entre 244 y 455 mm. Las hembras fueron más abundantes, grandes y pesadas que los machos en ambos sitios de pesca. Se identificó un patrón reproductivo con dos máximos anuales en BLP (marzo-junio y octubre-noviembre) y uno en BM (abril-agosto). Se identificó un patrón similar del IGS, FC e IHS por sexos en ambos sitios. La liseta mostró alometría negativa en crecimiento, rasgos de desovador total, desarrollo gonadal sincrónico por grupos y la L50% superior en hembras que en machos. Se recomienda reajustar la veda temporal por sitio de pesca y con base en la L50% ser precautorios en el tamaño de la luz de malla de las redes de pesca.