Egg development and fecundity estimation in deep-sea red ... - redmic

374 V.M. Tuset et al. / Fisheries Research 109 (2011) 373–378
November–December 2006 (n = 21), coinciding with the spawning
period October–May (López Abellán et al., 2002). Individuals were
recollected using bottom traps at depths of 600–1000 m (Carvalho
et al., 2007) to the south of Gran Canaria (Canary Islands, northeastern
Atlantic) (Fig. 1). Only fresh samples, the last day of collecting,
were taken to the laboratory for the posterior study: 14 females
we used for the morphological study of eggs and 30 females for the
fecundity estimation. Carapace width (CW in mm) and total weight
(TW in g) were taken from each crab.
2.2. Egg development
The fresh egg mass was separated from the pleopods, placed on
a mesh of 100 m, and washed with seawater under pressure to
detach all the eggs. Then some eggs were placed in two Petri dishes
with seawater under a compound microscope with reflected light.
Four images for each Petri dish (one by quadrant) were taken in
each female with a digital video camera (Basler A310, Vision Technologies,
Basler AG, Ahrensburg) for the automated morphology
analysis (Fig. 2). Approximately, 40 eggs were measured in each
quadrant. Image-Pro Plus version 4.1.0 software (Media Cybernetics,
Inc.) was used to calculate the following shape parameters and
indices: projected area (A in mm 2 ), maximum diameter (D in mm),
minimum diameter (d in mm), roundness (4A/( D 2 )), and aspect
ratio (D/d)(Russ, 1990). Egg morphology was described and classified
according to Arshad et al. (2006) and Walker et al. (2006) for
other brachyuran crabs, and colour changes of the egg mass considering
previous studies in Chaceon spp. (Wigley et al., 1975; Haefner,
1978).
2.3. Estimation of fecundity
The gravimetric method was applied to determine fecundity
(AFE, annual fecundity estimation), which was defined as annual
egg production, considering that spawning might occur only once
a year, using a subsample of 5% by wet weight of the egg mass
(Lowerre-Barbieri and Barbieri, 1993). Two methodological procedures
were applied: (a) in method 1 (February–March sample), the
fresh egg mass was separated from the pleopods, placed on a mesh
of 100 m, and washed with seawater under pressure to detach all
the eggs. Then the eggs were placed in Petri dishes with seawater
Fig. 1. Location of the study area.
under a compound microscope with reflected light, to count the
eggs using a hand counter. (b) In method 2 (November–December
sample), fresh egg masses were stored in 4% buffered formalin,
detached from the pleopod filaments using tweezers, placed on
Fig. 2. Digitalized image of eggs for morphological analysis: (A) original image; (B)
modified binary image.