Length–weight relationships for coastal fish species from the gillnet artisanal fishery in the central Mexican Pacific

This paper presents 43 length–weight relationships of coastal fish species of the families Carangidae, Lutjanidae and Haemulidae from the central Mexican Pacific. New maximum length values for 15 fish sepcies are included.     

Length–weight relationships for 24 fish species in a coastal lagoon of the Mexican South Pacific

Length–weight relationships were estimated for 24 species belonging to 16 families of fishes, representing a total of 15 312 measured fish, from the Carretas-Pereyra lagoon, Chiapas, Mexico. Significant length–weight relationships were found for all species. For 13 species, length–weight relationships are published for the first time.     

Length–weight relationships of deep-sea fishes from the western Bering Sea

Length–weight relationships are lacking for most deep-sea fishes. This study presents length–weight relationships for 42 species from the western Bering Sea. Results show significantly different relationships between females and males for 11 species and between juveniles and adults of four species. A plot of length–weight estimates, log a over b , showed the deep-sea fishes in this study to be more of the elongated shape compared with other marine fishes.     

Introduced predator elicits deficient brood defence behaviour in a crater lake fish

Introduced species represent one of the most serious global threats to biodiversity. In this field-based study, we assessed behavioural responses of brood tending cichlid fish to an invasive predator of their offspring. This was achieved by comparing parental defence responses of the endangered arrow cichlid (Amphilophus zaliosus), a fish species endemic to the crater lake Apoyo in Nicaragua, towards the bigmouth sleeper (Gobiomorus dormitor), a formidable predator of cichlid fry, and all other potential fish predators of offspring. The bigmouth sleeper was recently introduced into Apoyo but naturally co-exists with cichlids in a few other Nicaraguan lakes. Arrow cichlid parents allowed bigmouth sleepers to advance much closer to their fry than other predators before initiating aggressive brood defence behaviours. Interestingly, parents of a very closely related species, A. sagittae, which has coevolved with bigmouth sleepers in crater lake Xiloá, reacted to approaching bigmouth sleepers at comparable distances as to other predators of cichlid fry. These results provide a novel demonstration of the specific mechanism (i.e. naive parental behaviour) by which invasive predators may negatively affect species that lack the adequate behavioural repertoire.     

Length–weight relationships for 36 fish populations from a disturbed tropical estuary in northern Colombia

The study reports length–weight relationships for 36 species belonging to 20 families of the estuarine zone of the Sinú River in northern Colombia. To the best knowledge of the authors, this study presents the first study on length–weight relationships for 10 species worldwide as well as seven new maximum lengths.     

Depth and movement behaviour of the Pacific sleeper shark in the north-east Pacific Ocean

Satellite-linked radio telemetry was used to study the geographic movements and vertical movement behaviour of the Pacific sleeper shark Somniosus pacificus . The fish were tagged near Steller sea lion Eumetopias jubatus rookeries in the Gulf of Alaska during periods when Steller sea lions pups were most vulnerable to predation; when Steller sea lion pups first enter the water (July to August) and when Steller sea lion pups are weaned (April to May). Final locations recovered from most Pacific sleeper sharks (76%) were within 100 km of release locations, 16% were within 100–250 km and 8% were within 250–500 km. The most striking behavioural feature was their extensive, nearly continuous vertical movements. Median daily depth range was 184 m; the most time (61%) was spent between 150 and 450 m, but ascents above 100 m were common (58% of days). Median vertical movement rate was 6 km day⁻¹ and steady. The longest period of continuous vertical movement (> 60 m h⁻¹) was 330 h. Systematic vertical oscillations were most common (60%), followed by diel vertical migrations (25%) and irregular vertical movements (15%). The Pacific sleeper sharks travelled below the photic zone during the day and approached the surface at night. Pacific sleeper sharks appear to employ a stealth and ambush hunting strategy that incorporates slow vertical oscillations to search for prey, and cryptic colouration and cover of darkness to avoid detection by potential prey. The depth and geographic range of Pacific sleeper shark and Steller sea lions overlap near four important Steller sea lion rookeries in the northern Gulf of Alaska, so the potential exists for predation to occur. None of the tissues in the stomachs of the 198 Pacific sleeper sharks collected during a companion diet study, however, were identified as Steller sea lion.     

Length–weight relationships of eight fish species from the lower section of the Uruguay River (Río Negro, Uruguay)

This study reports length–weight relationships for Apareiodon affinis , Leporinus obtusidens , Cynopotamus argenteus , Loricariichthys melanocheilus , Parapimelodus valenciennis , Iheringichthys labrosus , Rhinodoras dorbignyi and Pachyurus bonariensis . Specimens were collected between 2006 and 2007 from the lower section of the Uruguay River. The study represents the first reference on weight–length relationships for three species and also provides the new maximum size for three species.     

Length–weight relationships for 12 fish species caught in Seyhan Dam Lake in southern Anatolia, Adana, Turkey

Presented are the length–weight relationships of 12 fish species [ Oncorhynchus mykiss (Walbaum, 1792); Cyprinus carpio, Linnaeus, 1758; Carassius carassius Linnaeus, 1758; Alburnoides bipunctatus (Bloch, 1782); Alburnus adanensis Battalgazi, 1944; Rutilus rutilus , Linnaeus, 1758; Squalis cephalus, Linnaeus, 1758; Tinca tinca (Linnaeus, 1758); Capoeta barroisi (Valenciennes, 1842); Silurus glanis Linnaeus, 1758; Gambussia affinis (Baird and Girard, 1853); and Sander lucioperca (Linnaeus, 1758)] from Seyhan Dam Lake, Turkey. This study provides the first estimation of length–weight relationships for two of the species ( A.   adanensis and C. barroisi ).     

Length–weight relationships for 20 species collected in the Jurumirim reservoir (Paranapanema Basin, Brazil)

Length–weight relationships were estimated for 20 species of the Jurumirim reservoir (southern Brazil): one Pimelodidae, one Callichthyidae, six Characidae, one Prochilodontidae, six Anastomidae, one Erythrinidae, two Curimatidae, one Paradontidae and one Cichlidae. The fishes were collected during 2001–2002 using three different types of fishing gear that allowed collection of both adult and juvenile specimens. The first reference of length–weight relationships for 12 species is provided.     

Biological Studies of the Pearl Spot Etroplus suratensis (Pisces,Cichlidae) from three Different Habitats in Sri Lanka

The morphometry, feeding habits and reproductive biology of Etroplus suratensis, an indigenous cichlid food fish, were studied for a period of one year on specimens from three different habitats in Sri Lanka. The morphometric studies implied that the length weight relationships are curvilinear. Macrophytic fragments formed the most important component of food, although detritus, diatoms, and animal matter are also ingested. First sexual maturity is attained in the length ranges 8.0-9.0 cm in females from brackish water habitats. Fecundity ranged from 700-3900 eggs in mature specimens. The wide range of the gonadosomatic index suggests that spawning occurs several times during the year.     

Diet of Pacific sleeper shark, a potential Steller sea lion predator, in the north-east Pacific Ocean

Pacific sleeper sharks Somniosus pacificus were captured near Steller sea lion Eumetopias jubatus rookeries during the period when Steller sea lion pups are most vulnerable to Pacific sleeper shark predation (first water entrance and weaning). Analysis of stomach contents revealed that teleosts were the dominant prey in August and cephalopods were the dominant prey in May ( n = 198). Marine mammals were found in 15% of stomachs regardless of season, but no Steller sea lion tissues were detected. Molecular genetic analysis identified grey whale Eschrichtius robustus and harbour seal Phoca vitulina remains in some Pacific sleeper shark stomachs. Most mammals were cetacean and at least 70% of the cetaceans were probably scavenged. Although Pacific sleeper shark and Steller sea lion ranges overlapped, so predation could potentially occur, the diet study suggested that predation on Steller sea lions is unlikely, at least when pups first enter the water or during weaning. Harbour seals were infrequent prey and may have been consumed alive. Pacific sleeper sharks consume fast-swimming prey like Pacific salmon Oncorhynchus sp., most likely live animals rather than scavenged animals. Pacific sleeper sharks appeared to be opportunistic consumers of the available prey and carrion, feeding both on the bottom and in the water column, and their diet shifted to teleosts and cetacean carrion as the fish grew larger.     

Spatial distribution and features of biology of Pacific sleeper shark Somniosus pacificus in the North Pacific

The results of the investigations of spatial and vertical distribution of Pacific sleeper shark Somniosus pacificus in the North Pacific Ocean conducted for many years are presented. In addition, the size distribution and features of biology of the species are studied. The largest abundance of the species is registered in the Bering Sea, western Gulf of Alaska, eastern Aleutian Islands, and Pacific waters of northern Kuril Islands and southeastern Kamchatka. The species is the most abundant near the bottom at the depth from 200 to 700 m and in the pelagic waters at a depth of 100–200 m. The average depths of the catches of Pacific sleeper shark substantially change over the year reaching minimum values in June and maximum values in December. Vertical daily migrations (to the water column at night and to the bottom during the day) are registered. The catches are represented by fish 26–352 cm in length, and sharks 100–200 cm in length prevail. The males are noticeably smaller than the females. In general, condition of the fishes decreases and feeding intensity increases with growth. Food composition substantially changes with the increase of body length: consumption of squids decreases and consumption of crustaceans, fishes, and fishery wastes increases. The food composition is slightly different in the females and males.     

Length–weight relationships of fish species caught in the Upper Uruguay River, Brazil

Length–weight relationships were estimated for 56 species, representing seven orders and 17 families of fishes from the Upper Uruguay River, Brazil. For most of these species, no length–weight relationships were previously available.     

Length–weight relationships of 21 fish species from the lower section of the Santa Lucía river basin (Canelones-Montevideo, Uruguay)

This study provides new length–weight relationship information for 21 neotropical fish species. Specimens were collected between 2004 and 2005 from the lower section of the Santa Lucía river basin (Uruguay). Presented are also the first reference on weight–length relationships for these 21 species, and new maximum sizes for six of these species.     

Length–weight and length–length relationships of fish species from the Aegean Sea (Greece)

We present the relationships between total (TL), fork (FL) and standard (SL) length for 37 fish species and the relationships between TL and wet weight for 40 fish species from the Aegean Sea (Cyclades; Greece). The relationships between TL, FL and SL were all linear (for all cases: r ² > 0.928). The values of the exponent b of the length–weight relationships ranged from 2.235 to 3.704.     

Specific biological features and genetic variation of Chinese sleeper <Emphasis Type="Italic">Perccottus glenii</Emphasis> (Odontobutidae) in aquatic bodies of Tyumen oblast

Specific biological features, morphology, and genetic variation of an invasive species, the Chinese sleeper Perccottus glenii, in several lake and river ecosystems of the Tyumen oblast have been studied. This species displays relatively high rate of linear and weight growths. The main feed of the Chinese sleeper in both the river and lake ecosystems is the chironomid larvae. The diet is richer in the river ecosystem; predation plays an important role; and cannibalism is observed. As has been shown, the qualitative and quantitative characteristics of the Chinese sleeper infestations with local helminth species are by one order of magnitude lower as compared with the native fish species. A significant infestation rate is observed only for Nippotaenia mogurndae, a parasite specific for the Chinese sleeper. The population of this introduced species displays a high genetic variation for DNA markers. The rate of polymorphic ISSR bands is 73% and Nei’s genetic diversity is 0.26. The Chinese sleeper populations in the not directly connected river and lake (distance, 90 km) display a genetic identity of 99.5%, suggesting the absence of genetic differentiation of local populations, explainable by their recent origin from a single source of invasion. Morphological differences of the Chinese sleeper in different ecosystems appear on the same genetic basis and suggest a wide reaction norm characteristic of this species, underlying its ecological plasticity.     

Length–weight and length–length relationships of three endemic butterflyfish species (Chaetodontidae) from coral reefs of the Northwestern Hawaiian Islands, USA

Length–weight and length–length relationships are presented for three species of butterflyfish endemic to the Hawaiian Islands and Johnston Atoll. From specimens collected within the Papahānaumokuākea Marine National Monument (PMNM), the weight–length relationships were determined for Chaetodon fremblii as W  = 0.029SL^3.17, Chaetodon miliaris as W  = 0.042 SL^3.00, and Chaetodon multicinctus as W  = 0.029SL^3.19 where weight, W , is reported in grams and standard length, SL, in centimeters. Length-frequency data and equations to calculate total length from standard length are also presented.     

Male-male competition and speciation: aggression bias towards differently coloured rivals varies between stages of speciation in a Lake Victoria cichlid species complex

Sympatric speciation driven by sexual selection by female mate choice on a male trait is a much debated topic. The process is problematic because of the lack of negative frequency-dependent selection that can facilitate the invasion of a novel colour phenotype and stabilize trait polymorphism. It has recently been proposed that male-male competition for mating territories can generate frequency-dependent selection on male colouration. Rare male cichlid fish would enjoy a fitness advantage if territorial defenders bias aggression towards male cichlid fish of their own colour. We used blue (ancestral type) and red phenotypes of the Lake Victoria cichlid species complex Pundamilia. We tested the aggression bias of wild-caught territorial blue male cichlid fish from five separate populations for blue vs. red rival male cichlid fish using simulated intruder choice tests. The different populations vary in the frequency of red male cichlid fish, and in the degree of reproductive isolation between red and blue, reflecting different stages of speciation. Blue male cichlid fish from a population that lack red phenotypes biased aggression towards blue stimulus male cichlid fish. The same was found in two populations where blue and red are reproductively isolated sister species. This aggression bias may facilitate the invasion of a novel colour phenotype and species coexistence. Blue male cichlid fish from two populations where red and blue are hybridizing incipient species biased aggression towards red stimulus male cichlid fish. Thus, after a successful invasion of red, aggression bias alone is not likely to generate frequency dependence required to stabilize the coexistence of phenotypes. The findings show that aggression bias varies between stages of speciation, but is not enough to stabilize the process of speciation.     

Variation in body condition of breeding Savi’s Warblers Locustella luscinioides: the reproductive stress and flight adaptation hypothesis revisited

Current theory suggests that mass change in adult birds while breeding may be adaptive (to reduce wing-loading during nestling feeding) or result from physiological stress. To test which might be more important in determining mass loss in breeding Savi’s Warblers (Locustella luscinioides), we used a new approach in which the variation in four indices of body condition was described: weight, fat score, muscle score and lean weight (i.e. excluding fat and muscle). We expected weight variations to be adaptive if they involved changes in fat and lean weight, whereas physiological stress should influence the muscle score to a greater extent. As in other species, females showed a greater variation in weight, and carried more fat, than males during the breeding cycle. During incubation, females had greater weight and fat score than males. The weight remained constant and lean weight declined in both sexes, whereas females increased in muscle, which probably reflects the regression of the reproductive organs. During the nestling stage, both sexes declined significantly in all four indices of condition, showing evidence of physiological stress. However, the greater decline in weight in females than in males is consistent with the flight-adaptation hypothesis, as are the cyclic changes in lean weight associated with the various nesting attempts. The fact that both sexes declined significantly in weight, muscle and lean weight with an increasing number of nesting attempts, but not in fat, which was recovered after each nestling period, also indicates that both reproductive stress and adaptive changes occur during breeding. When the whole breeding season was considered, females showed a greater decline in muscle than males, which we interpret to be evidence for a greater reproductive stress in females. We suggest that the small breast muscle size and depleted protein reserves at the end of the breeding period might influence future survival through impaired flight ability and a compromised post-breeding moult.