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

Gonadal development, spawning, growth and survival of the crayfish Procambarus llamasi at three different water temperatures

A study was done of the effect of three water temperatures (16, 21 and 26 degreesC on the growth, survival, gonad development and spawning rates of Procambarus ilamasi during a 90-day trial. Juveniles (<40 mm total length) were stocked at 76 org /m(2) density, and at a 1:1 M/F ratio. Growth improved in all treatments with increasing temperature, showing significant differences between sexes. Males grew more than females and achieved larger sizes with statistical differences (p<0.05) between treatments. Survival rate exhibited a negative relationship to temperature, with significant differences (p<0.05) between the 16 degreesC treatment and the others, but not between the 21 and 26 degreesC. Survival rate decreased from 90% at 16 degreesC to 42% at 26 degreesC. Ovary development increased as temperature increased. The gonadosomatic and maturation indexes were significantly different (p<0.05) between the 16 degreesC treatment and the others, but not between the 21 and 26 degreesC treatments. Spawning rate exhibited no relationship to temperature, with optimum results (22%) at 21 degreesC. (C) 2004 Elsevier B.V. All rights reserved