Home About us Contact
|
Home About us Contact | ||
|
|
||
Young-of-the-year Fish (young-of-the-year + fish)
Selected AbstractsJuvenile growth of two tilapia species in lakes Naivasha and Baringo, KenyaECOLOGY OF FRESHWATER FISH, Issue 3 2008J. R. Britton Abstract,,, Tilapia species in East African lakes often form the basis of commercial fisheries, with information on their population biology assisting their management. This study utilised otolith microstructure, with validation by modal progression analysis, to provide growth data for two tilapia species in two Kenyan lakes for the first time. Otolith microstructure revealed the growth rate of Oreochromis niloticus baringoensis, a sub-species endemic to Lake Baringo, was fast compared with populations of Oreochromis niloticus; mean daily growth rates were >0.50 mm·d,1 in fish between 12 and 53 mm total length. Growth of Oreochromis leucostictus in Lake Naivasha was also relatively fast when compared with the growth rates of other tilapia species, with mean daily growth rates of approximately 0.35,0.48 mm·d,1 in fish between 10 and 56 mm total length. Growth rates of both species were well described by the Gompertz model and were corroborated by modal progression analysis that revealed similar daily growth rates in modes of young-of-the-year fish. [source] Quantifying allowable harm in species at risk: application to the Laurentian black redhorse (Moxostoma duquesnei)AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2009Luis A. Vélez-Espino Abstract 1.When a species is identified for conservation, often the only way to effect recovery is to reduce the harm imposed by stressors threatening the survival of the species. Ideally all threats would be removed; however, this is often not feasible or practical. Within this context, a demographic approach is presented to assess how much human-induced harm could be allowed without impairing the persistence of the species. Harm is defined as a negative perturbation that can target one or more vital rates and life stages simultaneously. 2.Allowable harm, defined as a level of harm that will not jeopardize survival or recovery, will be a function of the vital rates affected by human actions, the sensitivity of population growth to changes in these vital rates (their elasticities), the population growth rate prevailing before harm occurs, and the set of demographic parameters considered safe for long-term persistence. This life-history based approach requires minimal data, can link demography with habitat-explicit information, is flexible enough to encompass complex life histories, and follows a precautionary approach. 3.Quantification of allowable harm could be applied to any species at risk. This approach is introduced by applying it to a Canadian population of a freshwater fish, the black redhorse (Moxostoma duquesnei), demonstrating that in the absence of habitat constraints population dynamics of this species are most sensitive to the survival of young adults, but population fitness is particularly sensitive to the loss of habitat used by young-of-the-year fish under current levels of habitat supply. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effect of wave exposure dynamics on gut content mass and growth of young-of-the-year fishes in the littoral zone of lakesJOURNAL OF FISH BIOLOGY, Issue 7 2010S. Stoll Total length, body mass and gut content mass of young-of-the-year (YOY) perch Perca fluviatilis, dace Leuciscus leuciscus and bleak Alburnus alburnus were recorded over the summer of 2006 at three littoral sites at Upper Lake Constance. In P. fluviatilis and L. leuciscus, gut content mass correlated positively with wave-induced energy flux (EF) of the respective site and sampling day, while no correlation of gut content mass with EF was found in A. alburnus. It was assumed that benthivorous P. fluviatilis and L. leuciscus profited from suspended or uncovered benthic food items generated by wave action at sites and periods with high EF. Alburnus alburnus, in contrast, feeding mainly on zooplankton in upper parts of the water column, could not profit from increased EF. In P. fluviatilis, increased gut content mass during periods of high EF resulted in higher growth rates. For L. leuciscus, no real growth rates in local fish populations could be determined, as individuals were less sedentary, and when increased growth occurred at sites during the periods of high EF, migration of fish levelled out the resulting size differences within few days. The results of this study show that dynamic habitat variables affect site profitability in the littoral zone of lakes, especially in benthivorous fishes. Therefore, dynamic habitat variables should be considered in addition to fixed habitat properties in analyses of habitat choice of fishes in the littoral zone of lakes. [source] Preparing sagittae for examination of daily growth increments of young-of-the-year fishes: a modification of the embed methodJOURNAL OF FISH BIOLOGY, Issue 2 2005G. Plaza A modification (termed the slide-glass-embed-method, SGEM) of the embed method for preparing fish sagittae is described. The SGEM is based on a very simple principle: a dome of mixed resin containing the embedded sagittae loses hardness after being heated and can be easily cut with dissecting scissors. [source] | ||||||||||