Reproductive performance of the Mesa silverside (Chirostoma jordani Woolman, 1894) under natural and controlled photoperiods

Chirostoma jordani is a native annual species inhabiting lacustrine waters of the Central Mexico Plateau. It is widely distributed and is currently facing high environmental pressures. Five experiments were performed to study the reproductive performance of this species. Four of the experiments were conducted in 270-L indoor recirculation tanks. Two males and one female at the first stage of reproduction were included in each test. A photoperiod of 14 light hours and 10 dark hours was used. In a fifth experiment, 10 females and 15 males were kept in an outdoor 3,000-L recirculation tank under natural photoperiod. The number of spawns, fertilised eggs and 30-day-old juveniles were counted and the survival rate was calculated. The results indicated significant differences (P< 0.05) between treatments. Higher spawn numbers and greater egg production were observed under controlled photoperiod, and higher numbers of juveniles and a higher survival rate were observed under natural photoperiod. The trials exhibited different patterns of egg production during the experiment. The egg production in the natural-photoperiod trials followed a polynomial curve model. In contrast, the trials under the controlled photoperiod showed an irregular pattern of increases and decreases in egg production.

Effects of salinity on growth and survival in five Artemia franciscana (Anostraca: Artemiidae) populations from Mexico Pacific Coast

Salinity is an important factor influencing growth and survival of aquatic organisms such as Artemia, a valuable aquaculture species. This study evaluated the effects of salinity on A. franciscana populations from different water bodies in Mexico’s Pacific Coast. With this purpose, five autochthonous bisexual Artemia populations were tested to assess their survival and growth values against salinities of 40, 60, 80, 100 and 120g/l, under laboratory conditions (25±2ºC; pH 8-10; constant light and aeration). The organisms were fed with 100mL of rice bran and 2L of Tetraselmis suecica (500 000cel/ml). The culture experiments were made in 200L plastic tanks, and survival and growth final values were obtained after 21 culture days. Survival and growth curves were determined by a regression analysis (R²). The significant differences between salinities were determined by ANOVA test (p<0.05). The best survival and growth rates were found at salinities of 100-120g/l. When the Mexican Artemia populations were cultivated at 40g/l of salinity, 100% mortality was observed in the juvenile stage. This study determined that survival and growth values of A. franciscana populations increased with salinity. The five A. franciscana populations presented significant differences in their survival rate under various salinity regimes. The studied populations experienced high mortality at salinities under 60g/l and over 200g/l, and especially during the metanauplius stage. The present study confirms that growth rates in Mexican A. franciscana populations from Pacific Coast habitats are not inversely proportional to salinity. These A. franciscana populations should be cultured at 100-120g/l of salinity to obtain better survival and growth rates. This data is useful to improve culture systems in aquaculture biomass production systems. Rev. Biol. Trop. 59 (1): 199-206. Epub 2011 March 01.

La salinidad es el factor más importante que modifica el crecimiento y la sobrevivencia de las poblaciones mexicanas de Artemia en el mundo. El efecto de este factor en las poblaciones costeras del Pacífico Mexicano ha sido poco estudiado. Cinco poblaciones bisexuales de Artemia provenientes de cuerpos de aguas costeras del Pacífico Mexicano, se estudiaron para determinar el efecto que tiene la salinidad de 40, 60, 80, 100 y 120g/l sobre la sobrevivencia y el crecimiento, en condiciones de laboratorio (25±2ºC, pH 8-10; luz y aireación continua). Los experimentos de cultivo fueron realizados en tanques de plástico de 200l. Los valores finales de sobrevivencia y crecimiento fueron determinados después de 21 días de cultivo. Los organismos fueron alimentados con 100ml de salvado de arroz y 2l de Tetraselmis suecica (500cel/ml). Las curvas de sobrevivencia y crecimiento fueron determinadas usando un análisis de regresión (R²). Las diferencias significativas entre los valores promedio a las distintas salinidades fueron determinadas por una prueba de ANDEVA (p<0.05). Las mejores tasa de sobrevivencia y crecimiento se encontraron a la salinidad de 100-120g/l. Cuando las poblaciones mexicanas fueron cultivadas a 40 g/l de salinidad, hubo una mortalidad del 100% de los organismos en estadio juvenil. A la salinidad de 80g/l, los valores de sobrevivencia y crecimiento, fueron menores que cuando se cultivaron entre 100 y 120g/l. Las cinco poblaciones bisexuales de A. franciscana presentaron diferencias significativas en sus tasas de sobrevivencia bajo las salinidades estudiadas. Las tasas de sobrevivencia fueron afectadas por la salinidad. Las poblaciones estudiadas experimentaron alta mortalidad a salinidades por debajo de 60 g/l y por arriba de 200g/l. Es importante mencionar que las altas mortalidades se observaron en el estadio metanauplios. El presente trabajo confirma que las tasas de crecimiento de las poblaciones que costeras del Pacífico Mexicano de A. franciscana no son inversamente proporcionales a la salinidad. Las poblaciones de A. franciscana deben de ser cultivadas a una salinidad de 100-120g/l para obtener mejores tasas de sobrevivencia y crecimiento. Estos datos permiten realizar mejoras en los sistemas de cultivo de este crustáceo para la obtención de biomasa para la acuicultura.

Age and growth of the tilapia, Oreochromis niloticus (Perciformes: Cichlidae) from a tropical shallow lake in Mexico

Age and growth of Nile tilapia (Oreochromis niloticus) were determined using 1 039 specimens collected in a tropical shallow lake of Mexico, from January to December 1993. Standard length of females ranged from 9.0 to 16.5 cm and males from 8.9 to 14.8 cm. The standard length-weight relationships for all individuals was BW=0.1207 SL2.469. The age data, derived from opercular bone readings, were used to estimate the growth parameters of the von Bertalanffy equation: or = 17.88 cm, K=0.3409, t o=-1.543, and W=149.21 g. The oldest male and female were 2.5 years old. The sex ratio (female:male) was of 1:1 (X²=0.02, p>0.05). Rev. Biol. Trop. 56 (2): 875-884. Epub 2008 June 30.

Se determinó la edad y el crecimiento de la tilapia del Nilo (Oreochromis niloticus) utilizando 1 039 organismos que fueron recolectados de Enero a Diciembre de 1993 en un lago somero tropical de México. La talla para las hembras osciló entre 9.0 y 16.5 cm longitud patrón y para los machos entre 8.9 y 14.8 cm. La relación peso total-longitud patrón para toda la población fue P=0.1207 L2.469. Los datos de edad obtenidos a través de los anillos del hueso opercular se utilizaron para estimar los parámetros de crecimiento del modelo de von Bertalanffy: o = 17.88 cm, K=0.3409, t o=-1.543 y P o = 149.21 g. La edad máxima obtenida para hembras y machos fue de 2.5 año. La proporción sexual (hembra:macho) para la especie fue de 1:1 (X²=0.02, p>0.05).

Desarrollo ovárico y su relación con las concentraciones séricas de 17β-estradiol y 17α-hidroxi- 4-pregnen-3-ona en hembras de primera maduración de pez blanco, Chirostoma humboldtianum (Atheriniformes: Atherinopsidae) / Association between ovarian development and serum concentrations of 17β-estradiol and 17α-hydroxy-4-pregnen-3-one in first maturation females of the shortfin silverside fish, Chirostoma humboldtianum (Atheriniformes: Atherinopsidae)

The first reproductive cycle of 50 females of the shortfin silverside, Chirostoma humboldtianum (Valenciennes) in culture conditions was analyzed. Ovarian developmental stages, gonadosomatic (GI) and hepatosomatic (HI) indexes were described. Histo-logical description of the ovaries and quantification of estradiol serum levels (E2) and 17α-hydroxy-4-pregnen-3-one (17-P4) by radioinmune assay were performed. Results showed a first reproductive season longer than six months. Females initiated spawning at the age of one year. Four ovarian maturation stages (I to IV) were determined during the spawning season and one (V) during the non-spawning season, the last one showed a non-defined pattern of development. The GI and HI indexes values indicate a positive lineal relation to body-weight only during the reproductive season (r² = 0.74 and r² = 0.86, P < 0.05, respectively). Histological analysis of the ovaries indicated that the species correspond to the pattern described as group-synchronous with multiple spawnings. The follicular population showed reproductive activity during the first stages of maturation with a predominant population of pre-vitellogenic follicles. As the ovarian maturation increased, the presence of all the follicular developmental stages was observed, with a tendency of an increase of vitellogenic and mature follicles. The concentration of circulating sexual steroid hormones of estradiol (E2) and 17α-hydroxy-4-pregnen-3-one (17-P4) were high during stage I (2.5 ± 0.7 ng/m L and 2.4 ± 0.3 ng/mLfor E2 and 17-P4, respectively); a decrease was observed during stage II, and the highest values were observed in stage IV (7.6 ± 2.1 ng/mL for E2 and 1.8 ± 0.9 ng/mL for 17-P4). The same pattern was observed during non-spawning season (ANOVA P < 0.05), these results are the first findings on the reproductive physiology of the shortfin silverside fish, suggesting an early steroidogenic activity in immature females. Furthermore, the species maintains its hormonal capacity during the post-spawning season, as it is supported by their follicular composition. The aforementioned will allow to have a better understanding of the mechanisms involved in their reproductive processes and to improve the mechanisms utilized to control their reproduction and for the production of eggs and larvae in culture conditions.

Se analizó el primer ciclo reproductivo de 50 hembras de pez blanco, Chirostoma humboldtianum (Valenciennes), en condiciones de cultivo. Se describieron los estadios de desarrollo ovárico y los índices gonadosomático (IG) y hepatosomático (IH). Se realizó una descripción histológica de los ovarios y se midieron los niveles séricos del estradiol (E2) y de la 17α-hidroxi -4-pregnen-3-ona (17-P4) por radioinmunoanálisis. Los resultados mostraron una primera época reproductiva de más de seis meses. Las hembras iniciaron sus desoves a la edad de un año. Se identificaron cuatro estadios de maduración ovárica (estadios I al IV) en la época de desoves y uno más (V) en la época no reproductiva, este último no tuvo un patrón de desarrollo definido. Los valores de los índices IG e IH mostraron una relación lineal positiva con el peso corporal únicamente en la época reproductiva (r² = 0.74 y r² = 0.86, P < 0.05, respectivamente). El análisis histológico de los ovarios indicó que la especie se clasifica como sincrónica por grupos múltiples. Los primeros estadios de maduración gonadal fueron caracterizados por ovarios cuyas poblaciones foliculares estuvieron compuestas predominantemente por folículos previtelinos. Conforme avanzó el proceso de maduración, se observaron todos los estadios de desarrollo folicular, con tendencia al incremento de folículos vitelinos y maduros. Durante el estadio I, las concentraciones de las hormonas esteroides sexuales circulantes de estradiol (E2) y de la 17α-hidroxi-4-pregnen-3-ona (17-P4) fueron altas (2.5 ± 0.7 ng/mL de E2 y 2.4 ± 0.3 ng/mL de 17-P4), se observó un decremento durante el estadio II y los valores más altos se registraron en el estadio IV (7.6± 2.1 ng/mL de E2 y 1.8 ± 0.9 ng/mL de 17-P4). Este mismo patrón fue observado durante la época de no desoves (ANDEVA P < 0.05); estos resultados son los primeros hallazgos en la fisiología reproductiva del pez blanco, los cuales sugieren una temprana actividad esteroidogénica en hembras inmaduras, además de que esta especie conserva su capacidad hormonal en la época posdesove, sustentada en su composición folicular. Lo anterior ayudará para comprender mejor los mecanismos involucrados en los procesos reproductivos y servirá de base para lograr su reproducción controlada y la obtención de huevos y larvas en condiciones de cultivo.

Growth of fresh-water prawn Macrobrachium tenellum (Smith, 1871) juveniles fed isoproteic diets substituting fish meal by soya bean meal

Growth parameters (standard length, weight, specific growth rate and daily weight gain) of prawn Macrobrachium tenellum juveniles fed 40 percent crude protein isoproteic diets substituting fish meal with soya bean meal at various levels (20, 40, 60, 80 and 100 percent) were evaluated for 45 days under laboratory conditions. Experimental diets were compared with a 100 percent fish meal based diet. Total survival was recorded for all the treatments at the end of the experiment. There were no significant differences (p > 0.05) for all the growth parameters among the dietary treatments. The initial mean weight (0.36 ± 0.10 g) increased almost three times (1.00 ± 0.13 g) after 45 days. The final specific growth fluctuated from 1.82 percent BW/d for the 60 percent soya bean meal inclusion diet, to 2.62 percent for the 100 percent fish meal diet. The mean final survival was 91.66 percent. Growth performance of M. tenellum juveniles was not affected by the dietary soya bean meal levels tested.

Os parâmetros do crescimento (comprimento padrão, peso, taxa de crescimento específica e ganho diário do peso) de juveniles do Macrobrachium tenellum alimentaram a 40 por cento a proteína crua as dietas isoproteic que substituem a refeição de peixes com feijão de soya a refeição nos vários níveis (20, 40, 60, 80 e 100 por cento) foi avaliada por 45 dias sob condições do laboratório. As dietas experimentais foram comparadas com uma dieta baseada da refeição de peixes de 100 por cento. A sobrevivência total foi gravada para todos os tratamentos no fim da experiência. Não havia nenhuma diferença significativa (p > 0.05) para todos os parâmetros do crescimento entre os tratamentos dietéticos. O peso médio inicial (0.36 ± 0.10 g) aumentado quase três vezes (1.00 ± 0.13 g) após 45 dias da cultura. O crescimento específico final flutuou de 1.82 por cento BW/d para a dieta do inclusion da refeição do feijão de soya de 60 por cento, a 2.62 por cento obtidos para a dieta da refeição de peixes de 100 por cento. A sobrevivência final média foi de 91.66 por cento. O desempenho do crescimento de juveniles do M. tenellum não foi afetado pelos níveis dietéticos da refeição do feijão de soya testados.

Morphological and genetic variation in seven species of the endangered Chirostoma "humboldtianum species group" (Atheriniformes: Atherinopsidae)

The Chirostoma "humboldtianum" group includes seven silverside species considered as a monophyletic assemblage because of their high genetic and morphological similarities. The group includes five moderately large species, "peces blancos" (117-300 mm standard length--SL) and two smaller species, "charales" (70-142 mm SL). These species are of great economical, cultural and ichthyological interest for local populations, and their management practices are controversial. We investigated the morphometric, meristic and allozyme variations of the seven species (13 populations) and related the variations with life history, habitat and management procedures. Nineteen morphometric variables, eight meristic variables (by multivariate analysis) and 23 allozyme loci of the seven species and populations of Chirostoma were compared. Principal component analysis (PC) of morphometric and meristic data indicate that both sets of data provided information to differentiate among the seven species. The variables that accounted for most of this differentiation were head length (HL), predorsal 1 length (PIL) and length of pelvic fin base (PfbL). PC and Discriminant Analysis (DA) with morphometric data also suggested the differentiation of populations within C. grandocule (83 correctly classified organisms), whereas PC and DA with meristic data differentiated populations of C. humboldtianum (80 correctly classified organisms). The most important morphometric variables for the differentiation were anal fin height (AfH), length of anal fin base (AfbL) and predorsal 2 length (P2L) and the meristic variables D2fR. PdS and AfR. The genetic variability data indicate changes in values of some of the species in relation to previously reported data. The present populations of C. grandocule show a reduction in He (0.002 vs. 0.009). Other species showed an increase; for instance, C. consocium consocium, C. humboldtianum, C. lucius, C. promelas and C. sphyraena averaged He = 0.069 vs 0.027. theta indicated significant genetic differentiation among the analysed species (0.247, S.D. 0.159) and theta s supported the morphological data that suggest intra-specific differentiation (0.360, S. D. 0.154).