On the formation of ephippia in some Cladocera (Crustacea) [Translation from: Zoologicheskie Zhurnal 61, 1425-1427, 1982]

The determination of relative connections between families and genera of Cladocera, necessary for the construction of their natural systems, must be based on various criteria, among them on the structure of the ephippia. Of particular interest is the study of the process of formation and structure of the ephippium in Macrothricidae, different representatives of which differ significantly among themselves according to this criterion. In this article are presented the results of an investigation of the features of formation of the ephippium in seven species of Macrothricidae and in the moinid Moina weismanni Ishikawa (Moinidae).

Quantitative determination of the timing of otolith ring formation from marginal increments in four marine teleost species from northwestern Australia

The sectioned otoliths of four fish species from a tropical demersal trawl fishery in Western Australia revealed a series of alternating trans-lucent and opaque zones in reflected light. The translucent zones, referred to as growth rings, were counted to determine fish ages. The width of the opaque zone on the periphery of the otolith section as a proportion of the width of the previous opaque zone (index of completion) was used to determine the periodicity of growth-ring formation. This article describes a method for modeling changes in the index of ring completion over time, from which a parameter for the most probable time of growth-ring formation (with confidence intervals) can be determined. The parameter estimate for the timing of new growth-ring formation for Lethrinus sp. 3 was from mid July to mid September, for Lutjanus vitta from early July to the end of August, for Nemipterus furcosus from mid July to late September, and for Lutjanus sebae from mid July to mid November. The confidence intervals for the timing of formation of growth rings was variable between species, being smallest for L. vitta, and variable between fish of the same species with different numbers of growth rings. The stock assessments of these commercially important species relies on aging information for all the age classes used in the assessment. This study demonstrated that growth rings on sectioned otoliths were laid down annually, irrespective of the number of growth rings, and also demonstrated that the timing of ring formation for these tropical species can be determined quantitatively (with confidence intervals.

Influence of Foliar Exposure, Adjuvants, and Rain-free Period on the Efficacy of Glyphosate for Torpedograss Control

The proportion of torpedograss tissue exposed to glyphosate at application rates of 0.28, 0.56, 1.12, 2.24, and 4.48 kg/ha affected control as measured by regrowth. The effect of tissue exposure was more pronounced as application rate decreased. This study suggests that higher rates of glyphosate need to be used during higher water levels, when less torpedograss tissue is exposed to herbicide spray and lower rates may be used during periods of low water levels. Addition of the water conditioning agent Quest (R) (0.25% v/v) to glyphosate spray mixtures diminished the influence of simulated rain events following glyphosate application. Twelve other adjuvants did not influence the effect of simulated rain events.

A video method for quantifying size distribution, density, and three-dimensional spatial structure of reef fish spawning aggregations

There is a clear need to develop fisheries independent methods to quantify individual sizes, density, and three dimensional characteristics of reef fish spawning aggregations for use in population assessments and to provide critical baseline data on reproductive life history of exploited populations. We designed, constructed, calibrated, and applied an underwater stereo-video system to estimate individual sizes and three dimensional (3D) positions of Nassau grouper (Epinephelus striatus) at a spawning aggregation site located on a reef promontory on the western edge of Little Cayman Island, Cayman Islands, BWI, on 23 January 2003. The system consists of two free-running camcorders mounted on a meter-long bar and supported by a SCUBA diver. Paired video “stills” were captured, and nose and tail of individual fish observed in the field of view of both cameras were digitized using image analysis software. Conversion of these two dimensional screen coordinates to 3D coordinates was achieved through a matrix inversion algorithm and calibration data. Our estimate of mean total length (58.5 cm, n = 29) was in close agreement with estimated lengths from a hydroacoustic survey and from direct measures of fish size using visual census techniques. We discovered a possible bias in length measures using the video method, most likely arising from some fish orientations that were not perpendicular with respect to the optical axis of the camera system. We observed 40 individuals occupying a volume of 33.3 m3, resulting in a concentration of 1.2 individuals m–3 with a mean (SD) nearest neighbor distance of 70.0 (29.7) cm. We promote the use of roving diver stereo-videography as a method to assess the size distribution, density, and 3D spatial structure of fish spawning aggregations.

Growth and reproduction of Moina rectirostris (Leydig) and Ceriodaphnia quadrangula (O. F. Muller) with feeding on detritus. [Translation from: Sbornik po prudovomu rybovodstvu, 79-89. Moscow, VNIRO, 1969.]

The significance of detritus in the nutrition of aquatic animals, especially of the small representatives of the zooplankton, has been studied very slightly. Research so far has established that in M. rectirostris with feeding on protococcal and single-celled green algae and bacteria the beginning of formation of eggs takes place in 2 - 4 days. The young appear in 4 - 6 days. In this study M. rectirostris and C. quadrangula are fed on detritus of natural origin in laboratory conditions. In order to determine the assimilability and productive: effect of detritus, the author set up experiments, permitting to characterize the rate of growth, speed of maturing and fertility of M. rectirostris and C. quadrangula with feeding of them on detritus of different composition and age.

Age validation of great hammerhead shark (Sphyrna mokarran), determined by bomb radiocarbon analysis

Preliminary validation of annual growth band deposition in vertebrae of great hammerhead shark (Sphyrna mokarran) was conducted by using bomb radiocarbon analysis. Adult specimens (n=2) were collected and thin sections of vertebral centra were removed for visual aging and use in radiocarbon assays. Vertebral band counts were used to estimate age, and year of formation was assigned to each growth band by subtracting estimated age from the year of capture. A total of 10 samples were extracted from growth bands and analyzed for Δ14C. Calculated Δ14C values from dated bands were compared to known-age reference chronologies, and the resulting patterns indicated annual periodicity of growth bands up to a minimum age of 42 years. Trends in Δ14C across time in individual specimens indicated that vertebral radiocarbon is conserved through time but that habitat and diet may inf luence Δ14C levels in elasmobranchs. Although the age validation reported here must be considered preliminary because of the small sample size and narrow age range of individuals sampled, it represents the first confirmation of age in S. mokarran, further illustrating the usefulness of bomb radiocarbon analysis as a tool for life history studies in elasmobranchs.