Development. Age. Growth

I. Development I. Development II. Age A. Types B. Stages C. Metamorphosis III. Growth Direct development: • all elasmobranchs 2 Types of Development in fishes: • most livebearing bony fishes • most fishes with large eggs Direct - no larval phase Indirect - larval phase present Indirect development: goosefish larva • most bony fishes Larvae: diverse shapes & forms goosefish adult 1 more larval forms Serranid Diodontid flatfish larva Larval Adaptations A) Myctophid sp 1: stalked eyes A and trailing gut B) Myctophid sp 2: elongated pectoral ray C) Serranidae sp 1: pelvic and dorsal spines B D) Serranidae sp 2: elaborate Acanthurid dorsal fin E) Ophidiidae, cavernous assfish (Porogadus gracilis): trailing gut Leptocephalus larvae D C E F) Holocentridae: head and snout spines F Indirect Development usually leads to… Leptocephalus larvae • found in 3 orders: – Elopiformes (tarpon) – Albuliformes (bonefish) – Angulliformes (true eels) Bipartite Life Cycle • larval stage lasts from 1 week to > 6 months • average pelagic larval duration (PLD) is about 30 d • long larval phase (>6 months – 3 yrs) • body morphology probably assists with the absorption of dissolved organic nutrients through their body wall Typical stages of development in Indirect Developers egg (embryo) hatching yolk sac ontogentic development in a jack (Trachurus symmetricus) improving swimming & sensory abilities Embryonic Period • organism entirely dependent on nutrition provided by the mother (yolk or placentallike nutrition) 1st feeding pre-flexion flexion post-flexion larvae • period begins when cells first divide; ends when embryo is free of the egg case but still absorbing nutrients from a yolk metamorphosis juvenile adult 2 Juvenile period Larval Period • miniature version of adult form (but immature) • characterized by the development of axial skeleton, fins, organs, and sensory abilities • fully formed skeleton, organs, fins, and pigmentation • mortality extremely high • larval features and adaptations for pelagic life are lost • flexion of the notochord – important early transition stage • transition from larval to juvenile periods can be quick or slow; and often accompanied by a change in habitat and prey types Benthic Juvenile vs. Benthic Adult adult Pelagic Juvenile vs. Benthic Adult • metamorphosis occurs during settlement (in demersal species) • metamorphosis occurs in the pelagic realm prior to settlement • many juveniles are colored differently than adults beaugregory damselfish juvenile Metamorphosis in flatfish: eye migration adult juvenile gopher rockfish adult gopher rockfish Metamorphosis in Parrotfish • adults have teeth fused into a beak • larvae have sharp canine teeth • larvae settle after a 25-50 day PLD • occurs at from 4-120 mm depending on species • eye migration takes from < 1 day to a few weeks • occurs via bone resorption and neurocranium reshaping • other structures change simultaneously (i.e. fin modifications, eye development, etc.) • metamorphosis occurs over a three week period – jaw transforms into a beak – phyrangeal jaw develops – gut becomes highly acidic to digest plant and coral material 3 Techniques for ageing fishes II. Age • known individuals (e.g., in aquaria or tagged) A. Techniques B. Maximum Ages C. Age at Maturity • environmental time marker (radiocarbon 14C from nuclear testing in 1950’s & 1960’s) • age marks on body parts – otoliths – scales – vertebrae – fin spines – fin rays – opercula – cleithrum shortraker rockfish, ≈100 years old Age studies using body hard parts otolith from goby Age studies using body hard parts • can have growth marks (like tree rings) corresponding to a unit of time (day or year) scale from Ide • determine age from counts of growth increments otolith from drum shark vertebra Maximum ages in fishes Age at maturity highly variable among species… short lifespans: annuals • Rivulus species, some gobies • related to lifespan (e.g., short lifespan, early maturity) annual killifish long lifespans: • rockfishes (Sebastes) -- several over 100 years, one species over 200 years • many sharks live several decades • often differs between sexes (w/ males maturing first usually) • maturity typically reached in first 1/4th of maximum lifespan • extremes: – male dwarf surfperch are born mature – spiny dogfish don’t mature until about 30 years old • reproduction doesn’t typically stop in old fishes (i.e., no reproductive senescence) rougheye rockfish: up to 205 years 4 Growth is very important in fish because... III. Growth • fish never stop growing... A. The importance of growth 30 B. Growth patterns in fishes Weight (lb.) 25 C. Factors that influence growth D. Measuring growth 20 15 10 5 0 0 5 10 15 20 25 30 Age (years) Growth is very important in fish because… • fish never stop growing • maturity is a function of size • size has a huge influence on reproductive output • size may influence susceptibility to predators Growth Patterns Indeterminate growth 1. continued growth after maturation 2. slow approach to asymptote, rarely achieved 3. stanzas: growth may vary in different stages (also need to know growth rate to parameterize some fisheries models) goliath grouper Age, sex, & maturity affect growth 1. growth slows with age, why? Growth Patterns cont. - increasing allocation to reproduction Mathematical Model of Fish Growth • von Bertalanffy growth equation • models asymptotic growth (doesn’t fit all species) 2. growth often differs between sexes, why? - different age of maturity - differential allocation to reproduction Lt = L∞(1-e-Kt) goliath grouper Lt = 2006mm(1-e-0.126t) where: • Lt is length at age t • L∞ is the theoretical max. length • t is age (“time”) • e is base of natural log • K is the Brody growth coefficient Bullock et al. 1992 5 Growth can only occur if there is surplus energy... Growth rate is set by… Surplus energy = energy from food – metabolic costs – energy excreted • physiology body maintenance & repair, digestion, movement • environment feces, ammonia, urea, mucus Other than growth, what can surplus energy be used for? Physiology: • growth is controlled by hormones secreted by the pituitary and the gonads II. Factors that affect growth: 1. Food (stress produces hormones that reduce growth) 2. Temperature 3. O2 4. Ammonia 5. Salinity 6. Exercise 7. Age & Maturity 8. Competition 9. Predators Food Temperature • quantity and quality matter • growth increases with temperature • seasonal variations in growth rate partially driven by abundance of food - chemical reactions and tissue synthesis faster • food is usually limited for fishes (e.g., Geoff Jones & - on reduced ration, fastest growth at lower temperatures - fish prefer optimal temperature for growth growth rate Graham Forrester: damselfishes on the GBR) - but metabolic costs increase too High ration Low ration temperature 6 Oxygen • more dissolved O2 è more growth Exercise - higher efficiency at converting food to tissue • increases growth rate - Why? Ammonia - Should increase metabolism and reduce growth, but... • more ammonia è less growth – increases growth hormone levels • un-ionized form (NH3) more toxic than ionized form (NH4+) – decreases aggressive interactions (which use energy and cause injury and stress) Salinity • each species has an optimal salinity for growth • at sub-optimal salinities, growth declines because the cost of osmoregulation increases Age & Maturity Competition • fastest growth when young (as a fraction of body mass) • decreases growth rate • mature fish invest energy into gonads and reproductive behavior • can increase variability in growth rate (through social interactions) (known as “growth depensation”) 140 y = 61.213LOG(x) + 27.553 Size vs. Age in the Pacific cubera snapper - limits food - increases stress competition in the blackeye goby 100 length (cm TL) 80 60 40 0 10 20 Age (years) 30 40 – increase growth by thinning prey population – decrease growth by causing prey to forage less or on lower quality food Growth rate Predators decrease growth of the blackeye goby 0.26 0.24 Predators absent 0.22 0.26 0.24 0.22 0.20 0.30 0.20 0.10 0.00 0 5 10 15 0 2.5 5 7.5 10 12.5 III. Measuring Growth • can increase or decrease growth 0.28 0.28 Population density Predators 0.30 0.40 Variability in growth (CV) 0.30 Growth rate Length (cm) 120 - can be measured in the lab or field lab • strength: tight control over environmental variables • weakness: lack of realism field • strength: realistic • weakness: little control over environmental variables Predators present 0.20 0 5 10 15 Population density 7 Direct measures of growth Measures of growth can be of: • Individuals - provides more information • Groups - easier to obtain • measure–re-measure known individuals advantages: most accurate; allows measurement of individual variation disadvantages: labor intensive • measure–re-measure a cohort advantages: less time consuming; don’t need to recover tagged fish and for each of these can be: • Direct - more reliable • Indirect - easier to obtain disadvantages: only gives average growth; may be biased • measure several cohorts (static method) advantages: least time consuming; don’t need to recover tagged fish & only sample one disadvantages: only gives average growth; most likely to be biased Static method Cohort method Mark–recapture • • • • • • • • • • • marks: clipped fins “cold brands” coded wire tags sonic tags genetic tags GPS position/data transmitting tags external tags (disks, streamers, beads) passive integrated transponders (PIT) injected paint, dye, or elastomer injected visual implant tags with codes chemically stained otoliths or bones Radiocarbon uptake Indirect methods of measuring fish growth 1. Radiocarbon uptake • measure uptake of radio-labeled amino acids by live epidermis on scales • get “instant” data on current growth rate • but, only get a relative estimate of growth rate 2. RNA/DNA ratio 3. Marks on bony structures RNA/DNA ratio • high ratio = high current growth rate • same advantages & disadvantages as for radiocarbon uptake 8 Marks on bony structures • one mark = one unit of time alive (e.g., one year, one day) Size vs. Age in the bridled goby 50 advantage: 40 Length (mm) – provides a real estimate of growth (e.g., mm per day, or kg per year) – only need to collect fish once & entire growth history is recorded disadvantages: 30 20 10 – can be labor intensive – marks may not represent the time intervals believed 0 – for many structures, must kill the fish to age it 0 – sample may be biased — only contains survivors (e.g., survivors may be fastest growers) 100 200 300 400 Age (days post-settlement) Potential problems: • increments may be formed at some interval other than what you think (e.g., may be sub-daily or sub-annual) – need to validate the periodicity of increment formation Types of hard part studies of growth • Population growth rate/age structure • Individual growth rates • increments can be lost – scales, bones, and vertebrae can be re-mineralized and partially resorbed • increments can be difficult to discern or interpret Population growth rate/age structure 140 Individual growth rates Pacific cubera snapper y = 61.213LOG(x) + 27.553 120 • relative growth rates or • estimate absolute growth rates by “back calculation” 100 length (cm TL) 80 • average growth rate 60 • variation in growth rate • age-related changes in growth rate • maximum age • age structure of population Length (cm) Information provided: 40 0 10 20 30 40 160 Gulf grouper 140 120 100 80 0 5 10 15 20 25 30 — allows comparison of growth rates of individuals over specific portions of life -- e.g., how fast does Chromis viridis grow in first month of life after settlement in dense populations vs. sparse populations? Age (years) 9 Back calculation Back calculation Steps: Steps: Body length (cm) 1. Determine mathematical relationship between body size and hardpart (usually otolith or scale) diameter (or radius) 10 1. Determine mathematical relationship between body size and hardpart (usually otolith or scale) diameter (or radius) 2. Measure the diameter of the hard part of the individual at the appropriate ages 3. Estimate the size of that individual at those ages by using the relationship between body size and hard part diameter 8 6 4 4. Subtract the smaller estimate of size from the larger one to get growth of the individual (divide by # of days, months, or years to get a growth rate)! 2 0 0 2 4 6 Otolith diameter (mm) 8 Back calculation Example: What is the rate of somatic growth over the 1st month of life after settling to the reef? Example: What is the rate of somatic growth over the 1st month of life after settling to the reef? size at settlement 10 • at settlement (30 days old), otolith diameter is 4 mm • one month later (60 days old) otolith diameter is 6 mm • estimated growth = about 2.5 cm/month size at one month PS Body length (cm) Body length (cm) Back calculation 8 6 4 2 0 0 2 4 6 Otolith diameter (mm) 10 8 6 4 2 0 8 0 2 4 6 Otolith diameter (mm) 8 Other types of otolith studies Back calculation Developmental stage • shape often changes with developmental stage Assumptions: 1. Hard-part growth is proportional to somatic growth 2. There is no variation in the relationship between body size and hard part diameter larva juvenile/adult Chemical concentrations as markers of past environments • trace elements • strontium/calcium ratio • O18/O16 ratio 10