The influence of the absence of light on the onset of first maturity and egg laying in the crayfish Procambarus (Austrocambarus) llamasi (Villalobos, 1955)

Procambarus llamasi is a crayfish species endemic to southeastern Mexico. Of all the portions of a species lifecycle to be understood, reproduction is the most vital. In order to better understand the effect of external factors on the reproductive development of P. llamasi, an experiment was done testing the influence of complete darkness (CD) and a natural light cycle (NL) on first maturity and egg laying. During the 90-day experiment, three tanks were covered with dark plastic to prevent light from entering (complete darkness, CD), and another three were covered with transparent plastic to allow a natural light cycle (14L:12D, NL). Sexually immature juveniles were placed in the tanks and their growth and sexual maturation monitored. At the end of the experiment, the general spawning mean was 24% for the CD treatment and 15% for the NL treatment. The maturation index was 4.04 for the CD and 3.88 for the NL, and the gonadosomatic index was 3.90 for the CD and 4.20 for the NL. In contrast to many other crayfish species, it is determined that complete darkness does not affect growth, survival or reproduction in P. llamasi. Reproductive development in this species may respond to other external factors such as hydrological cycles. (C) 2002 Elsevier Science B.V All rights reserved

Effect of the protein-lipids ratio on growth and maturation of the crayfish Procambarus (Austrocambarus) llamasi

The effect of six isocaloric diets with different protein (10%, 20% and 30%) and lipids (6% and 12%) contents was evaluated on growth and maturation of male and female juvenile P. llamasi crayfish. The experiment was carried out using individual plastic chambers within a closed, recirculating system with constant temperature. After 90 days, specific growth rate (SGR) values were generally low for both sexes. Lowest SGR for females was 0.4 with diet D1 (10/6) and highest was 0.7 with diet D4 (20/12). The lowest SGR for males was 0.3 with diet D1 (10/6) and the highest was 0.6 with diet D4 (20/12). Feed conversion ratio (FCR) varied from 1.1 to 1.8, and survival was generally high (> 80%) for both sexes. The Maturation Index (MI) behaved in a similar way to the Gonadosomatic Index (GI), manifesting a close relationship with dietary protein and lipids contents. Diet had a significant effect on maturation in females. The effect of protein and lipids content was significant with a direct relationship between these values and the MI and GI. Diets with the highest protein content had the best GI and MI values and all diets with 12% lipids had better MI and GI values than diets with 6%. Unlike the growth performance, the best maturation results were produced by the 30/12 diet. Based on the different observed effects of the diets on growth and maturation, it is recommended the use of a 20/12 diet for growth and a 30/12 diet for maturation. (c) 2005 Elsevier B.V. All rights reserved

Sex reversal and growth performance in juvenile females of the freshwater crayfish Cherax quadricarinatus (Parastacidae): Effect of increasing temperature and androgenic gland extract in the diet

Monosex male culture of C. quadricarinatus is proposed for increasing yields because males reach a larger size at harvest than females. An experiment was done to evaluate the effects of androgenic gland extract and temperature on sex reversal and somatic growth in early juvenile females. Females were exposed to the following experimental conditions: C: control food and temperature maintained at 26 ± 1°C; HT (high temperature): control food and temperature maintained at 28. 5 ± 1°C; VHT (very high temperature): control food and temperature maintained at 31 ± 1°C; AG: food with enriched with androgenic gland (1/10 dose for each juvenile per day) and temperature maintained at (26 ± 1)°C. The juveniles were weighed, sexed, and growth increment (GI) and growth rate (GR) were calculated twice a month. The HT and AG groups differed from the C group in GI and GR indicating a greater somatic growth. At the end of the experiment, the HT and AG groups had similar weight but only the HT group had enhanced oocyte diameter, with some vitellogenic oocytes compared to the C group. In the HT group, there was significant sex reversal, as indicated by development of male and intersex male characteristics in different individuals. Both temperature and AG diet have a high potential for culture of this species because of their enhancement of somatic growth; higher temperature increases the proportion of males, a desirable characteristic of cultured populations.Fil: Sánchez, Mariana. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; ArgentinaFil: Lopez, Laura Susana. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin