Effect of protein and lipids levels in a growth diet on adult whitebait Galaxias maculatus (Jenyns 1842)

Galaxias maculatus aquaculture objectives is to produce millions of eggs. Wild females are small (2 g), have quick sexual maturity and low mean fecundity (500 eggs/female), requiring larger fishes with higher fecundity. This study aim is to evaluate experimentally the effect of the levels of protein, lipid and dietary energy on weight increases in adults. Five independent experiments were performed at different sequential time periods at the UCT hatchery, Chile. Specimens were obtained from a) Crystalline sea return specimen catches in the Tolten estuary (4 -6 cm, 0.3-0.4 g.). b) Hatchery cultured fish. Fish were fed by hand ad libitum. In experiments 1 to 4, pelleted diets were prepared with 3 to 5 levels of protein (treatments 27 up to 57%), crumble size, three 100 L fibre ponds replicates. In experiment 5 the effect of two lipid levels (8 and 21%) was evaluated with commercial extruded Salmon Nutra Starter isoproteic crumble 1 diet at 63%, replicated in 4 ponds. The results show: A tendency to increased weight in all sizes with an increased protein level in the pelleted diet.A maximal adult growth is obtained with a diet containing a minimum of 37% crude protein, with 40% the optimal value. A higher % protein in the diet or growth in weight lower feed conversion ratio. The feed conversion ratio in the extruded diet reaches up to 0.5 and in the pelleted vary from 0.7 to 1.5. Fish 0.6 g fed with 63% protein, extruded commercial diet with two different lipid levels (8 and 21%, 20.40 and 23.84 MJ kg-1, PE/TE 0.62 and 0.71) increased weight the first month 67 and 105% each. It has been established that high-energy diets with optimal levels of protein and lipid are a good short-term solution to obtain G. maculatus of higher weight.

Three rivers and a fish: body shape variation in adult inanga (Galaxias maculatus) and implications for reproductive output

<p>Inanga (Galaxias maculatus) are the major component of New Zealand’s whitebait fisheries. Monitoring of freshwater-based adult populations in both North and South Island river systems suggests a general decline in numbers of fish, and specific streams and watersheds are of particular concern for some regional councils. Given this context, improved information about the environmental conditions that influence inanga’s reproductive output may help to inform appropriate management actions and improve the long term viability of these populations. The breeding biology of adult inanga has been the focus of considerable research effort, with restoration of spawning grounds further extending our knowledge of spatio-temporal patterns of spawning. However, the behaviour patterns and fates of adult fish outside of the spawning locations and seasons are poorly known, as are the factors that may influence the survival and development of pre-spawning stages of inanga. Variation in body shape and size influences multiple performance and fitness attributes, and has major implications for reproduction. My thesis aims to quantify relationships between morphology and reproductive output for adult inanga, and to investigate environmental factors that may influence morphological development. I collected inanga at two discrete stages of adult development: (i) pre-spawning stage adults at upstream habitats and (ii) spawning-stage adults collected at known breeding grounds during the spawning season. I photographed inanga in the field using a purpose-built aquarium and measured a set of morphological characteristics related to reproductive output and swimming ability. Specifically, I measured standard length, head depth, body depth and caudal peduncle depth. A subsample of adult inanga collected during the spawning season were returned to the laboratory and euthanized to measure aspects of their reproductive biology. Specifically, I measured reproductive output using gonad weight, I estimated maturity using the gonadosomatic index (GSI: weight of the gonad relative to total body weight), and I estimated energetic reserves using the hepatosomatic index (HSI: weight of the liver relative to total body weight). Pre-spawning stage inanga in the Waiwhetu Stream displayed deeper bodies than fish in either the Hutt or Wainuiomata Rivers, potentially due to higher concentrations of food. Inanga in the Wainuiomata River displayed slightly larger sizes prior to the spawning season and substantially larger bodies during the spawning season. Although the Waiwhetu Stream may have had a greater supply of food, high densities of fish in smaller stream systems could constrain adult growth. Spawning-stage adults collected from the Waiwhetu Stream had greater reproductive output than fish collected from the Hutt River, with a peak in spawning activity during May. Fish collected from spawning grounds in the Hutt River had lower reproductive output and two peaks in spawning activity during March and May. Inanga in the Hutt River also displayed greater within-month variation in the maturity of fish. My results suggest that spawning grounds in larger, more complex river systems (e.g., the Hutt River) may be supplied by inanga from a diverse range of main stem habitats and smaller tributaries further inland. Smaller systems (e.g., the Waiwhetu Stream) may be comprised of a more homogeneous population of inanga, and reproductive output of the system as a whole may be greater, but concentrated over a shorter time period. I hypothesise that the reproductive output from larger river systems may be more resilient to disturbance events (e.g., stock trampling of spawning grounds) because these systems (by virtue of their greater diversity of habitats and phenotypes of fish) may enable multiple opportunities for spawning. I suggest that larger rivers, such as the Hutt River, may be of disproportionate importance (independent of their total reproductive output) for the replenishment of inanga stocks.</p>

Three rivers and a fish: body shape variation in adult inanga (Galaxias maculatus) and implications for reproductive output

<p>Inanga (Galaxias maculatus) are the major component of New Zealand’s whitebait fisheries. Monitoring of freshwater-based adult populations in both North and South Island river systems suggests a general decline in numbers of fish, and specific streams and watersheds are of particular concern for some regional councils. Given this context, improved information about the environmental conditions that influence inanga’s reproductive output may help to inform appropriate management actions and improve the long term viability of these populations. The breeding biology of adult inanga has been the focus of considerable research effort, with restoration of spawning grounds further extending our knowledge of spatio-temporal patterns of spawning. However, the behaviour patterns and fates of adult fish outside of the spawning locations and seasons are poorly known, as are the factors that may influence the survival and development of pre-spawning stages of inanga. Variation in body shape and size influences multiple performance and fitness attributes, and has major implications for reproduction. My thesis aims to quantify relationships between morphology and reproductive output for adult inanga, and to investigate environmental factors that may influence morphological development. I collected inanga at two discrete stages of adult development: (i) pre-spawning stage adults at upstream habitats and (ii) spawning-stage adults collected at known breeding grounds during the spawning season. I photographed inanga in the field using a purpose-built aquarium and measured a set of morphological characteristics related to reproductive output and swimming ability. Specifically, I measured standard length, head depth, body depth and caudal peduncle depth. A subsample of adult inanga collected during the spawning season were returned to the laboratory and euthanized to measure aspects of their reproductive biology. Specifically, I measured reproductive output using gonad weight, I estimated maturity using the gonadosomatic index (GSI: weight of the gonad relative to total body weight), and I estimated energetic reserves using the hepatosomatic index (HSI: weight of the liver relative to total body weight). Pre-spawning stage inanga in the Waiwhetu Stream displayed deeper bodies than fish in either the Hutt or Wainuiomata Rivers, potentially due to higher concentrations of food. Inanga in the Wainuiomata River displayed slightly larger sizes prior to the spawning season and substantially larger bodies during the spawning season. Although the Waiwhetu Stream may have had a greater supply of food, high densities of fish in smaller stream systems could constrain adult growth. Spawning-stage adults collected from the Waiwhetu Stream had greater reproductive output than fish collected from the Hutt River, with a peak in spawning activity during May. Fish collected from spawning grounds in the Hutt River had lower reproductive output and two peaks in spawning activity during March and May. Inanga in the Hutt River also displayed greater within-month variation in the maturity of fish. My results suggest that spawning grounds in larger, more complex river systems (e.g., the Hutt River) may be supplied by inanga from a diverse range of main stem habitats and smaller tributaries further inland. Smaller systems (e.g., the Waiwhetu Stream) may be comprised of a more homogeneous population of inanga, and reproductive output of the system as a whole may be greater, but concentrated over a shorter time period. I hypothesise that the reproductive output from larger river systems may be more resilient to disturbance events (e.g., stock trampling of spawning grounds) because these systems (by virtue of their greater diversity of habitats and phenotypes of fish) may enable multiple opportunities for spawning. I suggest that larger rivers, such as the Hutt River, may be of disproportionate importance (independent of their total reproductive output) for the replenishment of inanga stocks.</p>

Effects of the cranial parasite Tylodelphys sp. on the behavior and physiology of puye Galaxias maculatus (Jenyns, 1842)

Diplostomatid digeneans are well-known manipulators of the behavior of their intermediate hosts. Unencysted metacercariae of Tylodelphys sp. inhabit the cranial cavity of the fish Galaxias maculatus; however, to date they have not been documented to alter their host behavior. The goal of this study was to evaluate the potential effects of Tylodelphys sp. inhabiting the cranial cavity of Galaxias maculatus on host physiology and swimming behavior as well as its reaction to a simulated predation attempt. Blind experiments in the lab were carried out on 56 fish that were filmed individually. The Fulton condition factor (K) was used as an approximation of nutritional status and a respirometry chamber was used to evaluate oxygen consumption rates of fish. Of the 56 fish, 21 were parasitized by Tylodelphys sp. (mean intensity = 30, range from 1 to 101). Parasitized and non-parasitized fish were similar in condition factor and oxygen consumption rates. Furthermore, the oxygen consumption rate of G. maculatus was not correlated with the abundance of Tylodelphys sp. However, parasitized fish more frequently swam close to the water surface, whereas non-parasitized fish more frequently swam at intermediate depths. When faced with a simulated predator attack, unparasitized fish showed more frequent fleeing behavior as well as a more intense post-fleeing activity. Collectively, these results suggest that Tylodelphys sp. inhabiting the cranial cavity of fish may alter their behavior predisposing them to predation by birds.

Whitebait conservation and protected areas at non-tidal rivermouths: integrating biogeography and environmental controls on īnanga (Galaxias maculatus) spawning grounds

Galaxias maculatus is a declining amphidromous fish that supports culturally-important whitebait fisheries in New Zealand and elsewhere in the Pacific. As a largely annual species, the seasonal productivity of spawning grounds has a strong influence on the availability of recruits. Spawning ground protection is urgently required to reverse historical degradation and improve prospects for the maintenance of sustainable fisheries. Although spawning habitat has been well characterised in tidal rivers where it is structured by water level changes on spring high tides, there has been no previous study of spawning in non-tidal rivermouths. We assessed seven non-tidal rivers over four months using a census survey approach to quantify spawning activity, identify environmental cues, and characterise fundamental aspects of the biogeography of spawning grounds. We report conclusive results that include a) identification of compact spawning reaches near the rivermouths, b) triggering of spawning events by periods of elevated water levels that were often of very short duration, suggesting that potential lunar cues were less important and that rapid fish movements had likely occurred within the catchment prior to spawning events, and c) consistent vertical structuring of spawning grounds above typical low-flow levels with associated horizontal translation away from the river channel, leading to increased exposure to anthropogenic stressors and associated management implications for protecting the areas concerned. These consistent patterns provide a sound basis for advancing the management of non-tidal rivermouths. Attention to flood management, vegetation control, and bankside recreational activities is required and may be assisted by quantifying spawning ground biogeography. The identification of rapid responses to environmental cues deserves further research to assess implications for floodplain connectivity management to support fish movements in emphemeral flowpaths, and as a potential source of bias in commonly-used fish survey methodologies.