Fish Biology

Egg cases of Bathyraja griseocauda were larger (140-142 mm in length) than those of Bathyraja scaphiops (88-90 mm in length) and their surface was relatively smooth, without denticles, prickles or any ornamentation. Egg cases of B. scaphiops had a relative coarse surface, covered with prickles of similar size. An identification key for the all described egg cases from Bathyraja occurring in the south-west Atlantic Ocean is provided.

This study utilized molecular tools to quantify the prevalence of predation during the vulnerable drifting larval life-history stage of lake sturgeon Acipenser fulvescens. How predators, the co-distributed prey community and abiotic environmental conditions (e.g., stream substrata) affected predation levels was quantified. Nightly D-frame drift net surveys were used to estimate the biomass of A. fulvescens and co-distributed prey. Gastrointestinal diet samples (n = 1,140) from 28 species of potential fish predators were collected during electrofishing surveys. Sampling was conducted for 17 days across 2015 and 2016. Based on DNA barcode analysis using sturgeon-specific mtDNA cytochrome oxidase I primers, A. fulvescens DNA was detected in 73 of 1,140 diet samples (6.40%) from 16 of the 28 predator species examined. A logistic regression model was used to analyse the effects of biotic and abiotic variables associated with the likelihood a predator had consumed larval A. fulvescens. Increasing lunar illumination and biomass of larval A. fulvescens increased predation rates on larval A. fulvescens. Higher discharge and greater biomass and proportions of alternative prey decreased predation rates of larval A. fulvescens. Predation rates were slightly higher in habitats with sand substrata. Most predator species preyed upon larval A. fulvescens at similar rates. The study revealed considerably higher incidence of predation on larval A. fulvescens than previous studies had documented using traditional morphological diet analysis. Co-distributed prey and abiotic environmental variables that affected the predation rates of a species of regional conservation concern can inform future management actions.

Leptopanchax opalescens (Myers, 1942) is a small seasonal killifish endemic to coastal drainages in the state of Rio de Janeiro, Brazil. Leptopanchax opalescens was recaptured in temporary open vegetation pools (22°42.35’S, 43°41.59’W) in the hydrographic basin of the Guandu River, state of Rio de Janeiro, Brazil, after eight years without records. Information on habitat and population parameters (Capture per unit area (CPUA), size, sex ratio and length-weight relationship (LWR)) are given to provide subsidies for the conservation of this species. Specimens were captured during the rainy season (January-April 2020) in shallow pools (mean depth = 21 ± 12 s.d. cm), with relatively acidic pH (5.2 ± 0.8) and low concentrations of dissolved oxygen (3.5 ± 1 mg/L). The estimated CPUA of the population was 0.89 fish/m2. The total length (TL) of males ranged from 21.1 to 28.8 cm, and females ranged from 17.0 to 31.2 mm. Males were significantly larger (t-test = 2.04, p < 0.05) than female...

To examine the effects of adding seeds powder and rocket Eruca sativa leaves to the diets of common carp Cyprinus carpio L. fish with percentages of 1, 2, and 3% of the total diet (the first, second, and third treatments), as well as the addition of rocket leaf powder to the fourth, fifth, and sixth diets, respectively, While the control diet, was empty of these additions (the seventh diet). Each treatment was replicated three times. These diets were used to feed common carp for 56 days. According to the statistical analysis's research results, the fish fed the fourth diet significantly superior surpassed the control diet and all other experimental diets in terms of growth criteria represented by the final weight, total weight gain, daily growth rate, relative, specific growth rate, and in terms of feed utilization: feed conversion ratio, feeding efficiency ratio and protein efficiency ratio. Except for the sixth treatment, the fed fish outperformed all other experimental treatments, and the second and fourth treatments regarding retained protein and protein production value. Fish were fed as the fifth treatment, significantly superior to the control diet. These results in the highest percentage of dry matter and crude protein for the edible portion of the body. Feeding fish on the fourth treatment resulted in the lowest proportion of ether extract, much lower than all the experimental diets.

This experimental study focused on the possible deterrent effect of permanent magnets on adult sandbar sharks, Carcharhinus plumbeus. Results showed that the presence of a magnetic field significantly reduced the number of approaches of conditioned C. plumbeus towards a target; indicating that adult C. plumbeus can be deterred by strong magnetic fields. These data, therefore, confirm that the use of magnetic devices to reduce shark bycatch is a promising avenue.

This experimental study focused on the possible deterrent effect of permanent magnets on adult sandbar sharks, Carcharhinus plumbeus. Results showed that the presence of a magnetic field significantly reduced the number of approaches of conditioned C. plumbeus towards a target; indicating that adult C. plumbeus can be deterred by strong magnetic fields. These data, therefore, confirm that the use of magnetic devices to reduce shark bycatch is a promising avenue.

Consumption of different age groups of juvenile, Norwegian, spring-spawning herring (Clupea harengus) by northeast Arctic cod (Gadus morhua) in the Barents Sea in 1992–1997 is estimated using cod stomach content data. We present a new approach to the problem of estimating consumption by fish. The new method is based on the estimation of digestion time for single prey items based on the difference between fresh weight at ingestion and weight in the stomach at time of sampling. Estimation is based on a gastric evacuation model for cod and area-specific sea temperatures. This is used to estimate the time (tmax) it takes for a prey to become digested to a stage where length is no longer measurable. Predation rate is then estimated for all prey with digestion time ≤tmax as number of prey eaten in the time range defined by tmax. This rate is combined with estimates of the proportion of the cod stock consuming the prey and area-specific abundance of cod, giving consumption of herring on a ...

Genetic structure of skipjack tuna Katsuwonus pelamis from the Indian region was investigated using sequence data of mitochondrial DNA (mtDNA) D-loop region. A total of 315 individuals were sampled from six major fishing grounds around the east and west coasts of India including the Andaman (Port Blair) and Lakshadweep (Minicoy) Islands. Nucleotide and gene diversities were high in all the sample collections. Significant genetic heterogeneity was observed for the mtDNA sequence data among sites (φ ST = 0•0273, P < 0•001). Analysis of molecular variance (AMOVA) showed significant genetic variation among four groups (φ CT = 0•0261, P < 0•05) which was also supported by spatial AMOVA results. The null hypothesis of single panmictic population of K. pelamis along the Indian coast can thus be rejected. Phylogenetic analysis of the mtDNA sequence data showed the presence of four clades of K. pelamis in the Indian waters. There was no clear pattern, however, of haplotypes and geographic location among samples. The results of this study suggest the occurrence of four genetically differentiated groups of K. pelamis across the coastal waters of India.

In June 2013, a record‐breaking female Isurus oxyrinchus (total length 373 cm, mass 600 kg) was captured by rod and reel off Huntington Beach, California, where it was subsequently donated to research and provided a rare opportunity to collect the first data for a female I. oxyrinchus of this size. Counts of vertebral band pairs estimate the shark to have been c. 22 years old, depending upon assumptions of band‐pair deposition rates, and the distended uteri and spent ovaries indicated that this shark had recently given birth. The stomach contained a c. 4 year‐old female California sea lion Zalophus californianus that confirmed the high trophic position of this large I. oxyrinchus, which was corroborated with the high levels of measured contaminants and tissue isotope analyses.

Сравнительная этология основывается на двух главных концептах — реальность существования и существенность форм единиц поведения — демонстраций. Первое означает, что они дискретизированы в потоке поведения, обладают типологической определённостью формы, т.е. она специфична у каждой демонстрации, что делает её узнаваемой для самих особей и для внешнего наблюдателя в независимых актах повторного предъявления: она не условность, рождённая наблюдателем для удобства классификации, и не кажимость, созданная его категоризирующим вниманием. Поэтому формы единиц поведения могут быть выделены и описаны объективно, на чисто структурной основе, без неявного привнесения функциональных моментов в процедуру описания. Второе означает, что специфический результат коммуникации (образование пары, сближение в ней партнёров и спаривание, изгнание захватчика или, наоборот, захват периферии  его территории после конфликта) достигается специфическими средствами, каждое из которых вполне определённым образом детерминирует последующие выборы поведения у другого участника (-ов) взаимодействия, как и у самого демонстратора, т.е. оно специализировано в определённом влиянии на него (-них). Эта специализация суть коммуникативная функция единиц поведения: каждое из подобных влияний специфично и статистически устойчиво, почему может быть установлено (а функция охарактеризована) на чисто функциональной основе без неявного привнесения структурных моментов (есть соответствующее влияние, резко меняющее поведение второй особи, или нет, безотносительно конкретных границ демонстраций во времени).

Критики сравнительной этологии, социобиологи на Западе и последователи Е.Н.Панова в нашей стране активно атакуют оба тезиса; по счастью, это везде попытки с негодными средствами. Реальность существования специфических единиц поведения, демонстраций, показана строго ещё в 1980е и многажды подтверждена после; их специализация как знаков или знаковых стимулов, участвующих в коммуникации и этим существенных для особей не меньше, а больше, чем для наблюдателя-этолога, поставленная под сомнение в годы концептуального кризиса сравнительной этологии (1970-80е гг.), постепенно подтверждалась всё больше в последующем, о чём я писал, и не раз (в том числе подтвердилась в анализе риска коммуникации — безусловном достижении критиков сравнительной этологии). Здесь рассказывается об исследования «подглядывания» и коммуникативных сетей в сообществах позвоночных, окончательно подтверждающих достижение специфического результата коммуникации специфическими средствами, опрокидывающем все построения критиков.