Comparative study of the reproductive biology of two congeneric and introduced goby species: implications for management strategies

A full understanding of life history characteristics of invasive species is a fundamental prerequisite for the development of management strategies. Two introduced goby species (Rhinogobius cliffordpopei and Rhinogobius giurinus) have established highly abundant populations in Lake Erhai (China). In the present study, we examined the reproductive biology of these two species with the aim of improving the efficiency of management strategy. The results indicated that R. cliffordpopei spawned from February to June, whereas R. giurinus spawned from April to August. Rhinogobius cliffordpopei showed higher gonado-somatic indices and had larger eggs than R. giurinus. The adult sex ratio of R. cliffordpopei was female skewed, but that of R. giurinus was equal. Rhinogobius cliffordpopei showed a male-skewed sexual size dimorphism, whereas the body size of R. giurinus varied only slightly between males and females. The different reproductive traits appear as a crucial biologic aspect for developing control programs. Specifically, control measures should be implemented and/or intensified from September to February for R. cliffordpopei and from January to April for R. giurinus. The body size of the smaller R. cliffordpopei females is the determinant for minimal mesh size of the nets used in physical removals of R. cliffordpopei.A full understanding of life history characteristics of invasive species is a fundamental prerequisite for the development of management strategies. Two introduced goby species (Rhinogobius cliffordpopei and Rhinogobius giurinus) have established highly abundant populations in Lake Erhai (China). In the present study, we examined the reproductive biology of these two species with the aim of improving the efficiency of management strategy. The results indicated that R. cliffordpopei spawned from February to June, whereas R. giurinus spawned from April to August. Rhinogobius cliffordpopei showed higher gonado-somatic indices and had larger eggs than R. giurinus. The adult sex ratio of R. cliffordpopei was female skewed, but that of R. giurinus was equal. Rhinogobius cliffordpopei showed a male-skewed sexual size dimorphism, whereas the body size of R. giurinus varied only slightly between males and females. The different reproductive traits appear as a crucial biologic aspect for developing control programs. Specifically, control measures should be implemented and/or intensified from September to February for R. cliffordpopei and from January to April for R. giurinus. The body size of the smaller R. cliffordpopei females is the determinant for minimal mesh size of the nets used in physical removals of R. cliffordpopei

Habitat segregation between two congeneric and introduced goby species

Spatial segregation is one of the most important mechanisms that facilitates coexistence among competing species. Large populations of two introduced and congeneric goby species (Rhinogobius giurinus and Rhinogobius cliffordpopei) now co-occur in Lake Erhai, a plateau lake in the Yunnan-Guizhou Plateau (China). Herein we quantified the spatio-temporal distribution of the two species to determine whether spatial segregation occurred within the same ecosystem. A total of 67,819 individuals of R. giurinus and 36,043 of R. cliffordpopei were sampled across four seasons. The results indicated that R. giurinus mostly occupied profundal habitat (PH) while R. cliffordpopei mainly used littoral habitat (LH). Correlation analysis revealed the abundance of R. giurinus was positively associated with deep water, silt and coarse sand substrata, whereas the distribution of R. cliffordpopei was positively associated with high densities of macrozooplanktons and high abundances of other fish species, high concentration of dissolved oxygen and high densities of submerged macrophytes. Except in spring, the body condition of R. giurinus was significantly higher in the PH than in the LH. The body condition of R. cliffordpopei did not differ significantly between habitats in the four seasons. These findings demonstrate that the two congeneric and introduced goby species occupy distinct habitats, indicating that spatial segregation enables coexistence of the two invasive species at high abundances within an ecosystem.Spatial segregation is one of the most important mechanisms that facilitates coexistence among competing species. Large populations of two introduced and congeneric goby species (Rhinogobius giurinus and Rhinogobius cliffordpopei) now co-occur in Lake Erhai, a plateau lake in the Yunnan-Guizhou Plateau (China). Herein we quantified the spatio-temporal distribution of the two species to determine whether spatial segregation occurred within the same ecosystem. A total of 67,819 individuals of R. giurinus and 36,043 of R. cliffordpopei were sampled across four seasons. The results indicated that R. giurinus mostly occupied profundal habitat (PH) while R. cliffordpopei mainly used littoral habitat (LH). Correlation analysis revealed the abundance of R. giurinus was positively associated with deep water, silt and coarse sand substrata, whereas the distribution of R. cliffordpopei was positively associated with high densities of macrozooplanktons and high abundances of other fish species, high concentration of dissolved oxygen and high densities of submerged macrophytes. Except in spring, the body condition of R. giurinus was significantly higher in the PH than in the LH. The body condition of R. cliffordpopei did not differ significantly between habitats in the four seasons. These findings demonstrate that the two congeneric and introduced goby species occupy distinct habitats, indicating that spatial segregation enables coexistence of the two invasive species at high abundances within an ecosystem

Growth and energy budget of juvenile lenok Brachymystax lenok in relation to ration level

We evaluated the effect of ration level (RL) on the growth and energy budget of lenok Brachymystax lenok. Juvenile lenok (initial mean body weight 3.06 +/- 0.13 g) were fed for 21 d at five different ration levels: starvation, 2%, 3%, 4% bwd (body weight per day, based on initial mean values), and apparent satiation. Feed consumption, apparent digestibility, and growth were directly measured. Specific growth rates in terms of wet weight, dry weight, protein, and energy increased logarithmically with an increase in ration levels. The relationship between specific growth rate in terms of wet weight (SGR(w), %/d) and RL (%) was characterized by a decelerating curve: SGR(w)=-1.417+3.166ln(RL+1). The apparent digestibility coefficients of energy exhibited a decreasing pattern with increasing ration level, and there was a significant difference among different RLs. Body composition was significantly affected by ration size. The relationship between feed efficiency rate in terms of energy (FERe) and RL was: FERe=-14.167+23.793RL-3.367(RL)(2), and the maximum FERe was observed at a 3.53% ration. The maintenance requirement for energy of juvenile lenok was 105.39 kJ BW (kg)(-0.80)/d, the utilization efficiency of DE for growth was 0.496. The energy budget equation at satiation was: 100IE=29.03FE+5.78(ZE+UE)+39.56 HE+25.63 RE, where IE is feed energy, FE is fecal energy, ZE+UE is excretory energy, HE is heat production, and RE is recovered energy. Our results suggest that the most suitable feeding rate for juvenile lenok aquaculture for wet weight growth is 2.89% bwd, whereas for energy growth, the suggested rate is 3.53% bwd at this growth stage

Trophic niche differences between two congeneric goby species: evidence for ontogenetic diet shift and habitat use

Food partitioning is one of the primary mechanisms facilitating the stable co-occurrence of competing species, but very few studies have investigated how food resource use of competing and closely related species varies with life-history stages and habitats. In Lake Erhai (China), the trophic niche of 2 congeneric and co-occurring invasive goby species (Rhinogobius cliffordpopei and R. giurinus) was examined to test the existence of an ontogenetic diet shift and to determine potential differences in trophic niche between species within a habitat and between habitats (i.e. littoral and profundal) within species. Results obtained from gut content and stable isotope analyses revealed a strong trophic niche shift during ontogeny, whereby juveniles mainly consumed macrozooplankton while sub-adults and adults increasingly consumed aquatic insects and Tubificidae. The trophic niche of juveniles was similar between species in each of the 2 habitats but significantly different for sub-adults and adults, notably in littoral habitat. Moreover, the trophic niche was similar between habitats for juveniles of each species, whereas it differed significantly between habitats for sub-adults and adults. This study demonstrates the importance of ontogeny and shows that habitat use can significantly affect food resource use and trophic relationships between 2 co-occurring fish species.Food partitioning is one of the primary mechanisms facilitating the stable co-occurrence of competing species, but very few studies have investigated how food resource use of competing and closely related species varies with life-history stages and habitats. In Lake Erhai (China), the trophic niche of 2 congeneric and co-occurring invasive goby species (Rhinogobius cliffordpopei and R. giurinus) was examined to test the existence of an ontogenetic diet shift and to determine potential differences in trophic niche between species within a habitat and between habitats (i.e. littoral and profundal) within species. Results obtained from gut content and stable isotope analyses revealed a strong trophic niche shift during ontogeny, whereby juveniles mainly consumed macrozooplankton while sub-adults and adults increasingly consumed aquatic insects and Tubificidae. The trophic niche of juveniles was similar between species in each of the 2 habitats but significantly different for sub-adults and adults, notably in littoral habitat. Moreover, the trophic niche was similar between habitats for juveniles of each species, whereas it differed significantly between habitats for sub-adults and adults. This study demonstrates the importance of ontogeny and shows that habitat use can significantly affect food resource use and trophic relationships between 2 co-occurring fish species

Maintaining Economic Value of Ecosystem Services Whilst Reducing Environmental Cost: A Way to Achieve Freshwater Restoration in China

Freshwater fisheries are central to food security in China and this remains one of the most important priorities for the growing human population. Thus, combining ecosystem restoration with economics is pivotal in setting successful conservation in China. Here, we have developed a practical management model that combines fishery improvement with conservation. For six years, a ban on fertilizer and a reduction of planktivorous fish stocking along with the introduction of both mandarin fish Siniperca chuatsi and Chinese mitten crab Eriocheir sinensis was apparent in Wuhu Lake, a highly eutrophic lake located in the middle reaches of the Yangtze River. Annual fish yield decreased slightly after the change in management, whereas fisheries income increased 2.6 times. Mandarin fish and Chinese mitten crab accounted for only 16% of total fisheries production but for 48% of total fisheries income. During this six year period, water clarity increased significantly from 61 cm to 111 cm. Total nitrogen, total phosphorus and chlorophyll decreased significantly from 1.14 to 0.84 mg/L, 0.077 to 0.045 mg/L, and 21.45 to 11.59 mu g/L respectively, and macrophyte coverage increased by about 30%. Our results showed that the ecological status of shallow lakes could be rapidly reversed from eutrophic to oligotrophic using simple biomanipulation, whilst maintaining fisheries economic value. It also offers a better approach to shallow fisheries lake management in Asia where traditionally the stocking of Chinese carp and use of fertilizers is still popular