标题：Estimates of the size at first maturity from Gonadossomatic Index (IGS) data: Oligosarcus jenynsii, Oligosarcus robustus, Hoplias malabaricus, Cyphocharax voga, Astyanax fasciatus (Characiformes), Parapimelodus nigribarbis, Pimelodus maculatus
出版社：Faculdade de Biociências, Pontifícia Universidade Católica do Rio Grande do Sul
摘要：Correct estimates of the size at first maturity (L50) are necessary for fish
stock management and different methods have been proposed. In this study we
apply a modified logistic model to estimate the size at first maturity from
Gonadossomatic Index (GSI) data. This research results from a monthly sample
program carried out in Lagoa do Casamento (November 2002 to April 2004) and Lago
Guaíba (June 2005 to May 2006), Rio Grande do Sul, Brazil. The specimens were
sampled using gillnets of different mesh sizes (30 meters long; 15, 20, 25, 30,
35, 40, 50, 60 e 70 mm between knots, 36 hours/month). The length at first
maturity (LMAT) of each fish specie was estimated trough a modified logistic
equation, adjusted from GSI data through Levenberg-Marquardt algorithm (SPSS
11.5): IGSMED=IGSMIN+(IGSMAX-IGSMIN)/ (1+exp(-Tax*(LTOT-LMAT))); where IGSMED is
the average GSI for females in each size class; IGSMIN is the average GSI for
juvenile females; IGSMAX is the average GSI for adult females; Tax is the rate
of changing from juvenile to adult; LTOT is the average total length of each
size class; and LMAT is the length at first maturity. For species with sample
size too small to adjust the model, the first maturation (LMIN) were estimated
as the total length of the smaller female with GSI equal or larger than 30% of
the maximum registered GSI for the specie. The length at first maturity of
Oligosarcus jenynsii was estimated as 16.2cm (LMAT; SE=0.167). For Oligosarcus
robustus the reproductive activity starts at 21.4cm (LMAT; SE=0.463) of total
length. The first maturity was determined as 13.9 cm (LMIN) for Hoplias
malabaricus females. Cyphocharax voga starts to reproduce with 18.5cm (LMAT;
SE=0.738) of total length. The length of first maturity for Astyanax fasciatus
was estimated as 12.2cm (LMAT; SE=0.661). For Pimelodus maculatus females the
reproductive activity starts with 18.0cm (LMIN). The first maturity was
estimated at 8.0cm (LMIN) for Parapimelodus nigribarbis. Hoplosternum littorale
starts to reproduce with 14.1cm (LMAT; SE=0.199). For Loricariichthys anus
females, first maturity was estimated at 27.0cm (LMAT; SE=1.151). The length at
which Pachyurus bonariensis starts reproduction is 17.2cm (LMAT; SE=2.024).
Finally, the first maturity of Trachelyopterus lucenai was estimated as 13.7cm
(LMAT; SE=0.537).
关键词：Fish, first maturity, Guaíba, Laguna dos Patos, Lagoa do Casamento, GSI.
